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MODERN HISTORY LIBRARY |
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CHAPTER XXIII. EUROPEAN
SCIENCE IN THE SEVENTEENTH AND EARLIER YEARS OF THE EIGHTEENTH CENTURIES.
(1) MATHEMATICAL AND PHYSICAL SCIENCE.
The seventeenth century is notable in the history of science for the development of
those ideas which distinguish its modem treatment from that customary in the
ancient and medieval world, and for the recognition of the principle that
scientific theories must rest on the result of observations and experiments.
The influence
of the Renaissance was felt in arts and letters a generation or more before it
affected men of science; but towards the end of the sixteenth century
mathematicians began to open up new fields of study, and a few years later the
ideas current in Mechanics and Physics were subjected to the test of
experiment. These researches were undertaken independently in different parts
of western Europe; and the printing-press, the general use of one language
(Latin), and increasing facilities for travel, rendered the dissemination of
new ideas comparatively easy. For the first time in the history of science,
British writers took a prominent part in its development.
In the early
years of the seventeenth century the views of astronomers were recast; the
principles of Dynamics were laid down; a science of Physics was initiated; and,
lastly, new branches of Mathematics were created and applied to these and other
subjects. Before the close of the period treated in this volume the language of
Mathematics had been settled; the use of Analytical Geometry and the
Infinitesimal Calculus had become familiar; the theory of Mechanics had been
elaborated, and it had been shown that the planetary motions could be explained
by the same laws as those affecting terrestrial bodies; a large part of the
theory of fluids had been established; the geometrical and physical theories of
Light had been worked out in considerable detail; something had been done
towards creating a theory of Acoustics; and the fundamental problems of
vibratory motion were being attacked.
We shall best
be able to estimate the progress of mathematical and physical science during
the seventeenth century, if we begin by noting the extent of the knowledge
current about 1575 or 1580.
Turning
first
to the subject of Pure Mathematics, we may say that in
Geometry the results
attained by Euclid were then generally accessible, and the
more elementary
properties of Conic Sections were known; but the standard of
knowledge was
considerably below that of the Greeks. In Arithmetic the
fundamental
processes and the use of the Arabic symbols were well
established, though the
methods employed were cumbrous. Algebra was syncopated—that
is,
abbreviations were used for those operations and quantities
which constantly
recur, but such abbreviations were subject to the rules of
grammatical
construction. Lastly, the more elementary propositions in
Trigonometry were
known. This, knowledge would seem to be but a scanty equipment
for the attack
of new problems; but in questions of Pure Mathematics it was
used with more
effect than could have been anticipated or than was supposed a
few years ago. As to applied science, however, an astonishing ignorance
still prevailed.
Of the
several branches of applied science, the mechanics of rigid bodies is the
oldest. The science of Statics, so far as it related to parallel forces, had
been placed on a satisfactory basis by Archimedes, who rested it on the axiom
that two equal weights suspended from a rigid weightless bar at equal distances
from a fulcrum on which the bar rested would be in equilibrium. But the
question of the resultant of forces, acting on a particle, had not been
included in his discussions, and was still an unknown branch of the subject,
with the exception of the result of the parallelogram theory for the
particular case of two forces at right angles to each other acting on a
particle. Dynamics as a science did not exist. It was indeed asserted on the
authority of Aristotle, that the rate at which bodies fell varied directly as
their weights—a statement which could have been easily disproved, had it
been subjected to the test of experience; but no theory of the subject had
been propounded even on this false premiss.
In Astronomy,
the authority of Ptolemy was, about 1580, almost as well established as that of
Aristotle in science, though here, at any rate, observations of the stars were
available, due partly to the general interest in Astrology. According to the
Ptolemaic theory the Earth was at the centre of the universe, and around it
revolved in successive order the Moon, Mercury, Venus, the Sun, Mars, Jupiter,
Saturn, and the fixed stars. These bodies were supposed to move uniformly along
the circumferences of circles (epicycles) whose centres revolved uniformly
along the circumferences of other circles—the centres of the last-mentioned
circles (eccentrics) being at points near, but not coinciding with, the centre
of the earth.
As time went
on, and more accurate observations were accessible,
The only
other subjects to which Mathematics had been applied and which need be here
mentioned are Optics and Hydrostatics. In Optics the law of reflexion was
known, and solutions of some of the more elementary geometrical problems
connected with rays reflected at spherical surfaces were familiar through the
writings of the Greeks and Arabs. In Hydrostatics the theory of floating bodies
had been given by Archimedes, and probably his results were accessible to
students. Of other branches of Physics, such as Sound and Electricity, we may
say that the little that was known is not worth describing; in these subjects
the authority of Aristotle was unquestioned. Lastly, such knowledge of
Chemistry as existed was mixed up with Alchemy, and was practically worthless.
This rapid
summary will bring out more clearly than any general statement the fact that
the origin of physical science and modern Mathematics cannot be assigned to a
date earlier than the close of the sixteenth century. Into a world whose
knowledge was so slight and limited a ferment of new ideas was then introduced,
and within a few years the position of the subjects was revolutionised, and the
number of thinkers interested in them was greatly increased.
It will be
most convenient to review the subjects considered in the present section
science by science—and, first, to trace their development very briefly to the
middle of the seventeenth century, and, then, to take up again the history of
each science to the end of the first quarter of the eighteenth century, which
marks the close of the period treated in this volume. We begin as before with
the subjects of Pure Mathematics.
Introduction of logarithms and decimals. The power of
Arithmetic in dealing with numerical calculations involving multiplication or
division was greatly increased by the invention of logarithms. Their discovery
was due to Napier of Merchistoun (1550-1617), who published his results in
1614, though he had privately
The decimal
notation for fractions was introduced about the same time as logarithms, and it
was certainly used as an operative form by Briggs in 1617. A somewhat similar
notation had been employed a few years earlier by Stevinus, Rudolff, Bürgi,
and Napier, though probably only as a concise way of stating results. Up to
that time fractions had been commonly written in the sexagesimal notation.
The
introduction of these discoveries brought Arithmetic into its modern form, and
subsequent improvements have been largely matters of detail.
At the close
of the sixteenth century the art of Algebra began to assume its modem or
symbolic form. In this it has a language of its own and a system of notation
which has no obvious connexion with the things represented, while the
operations are performed according to rules distinct from those of grammar. The
credit of introducing this was mainly due to Francis Vieta of Paris
(1540-1603). In his principal work, published in 1591, he used letters for
both known and unknown positive quantities. In it he also introduced for the
powers of quantities a notation which was a marked advance on that previously
prevalent by which new symbols had been introduced to represent the square,
cube, etc., of quantities which had already occurred in the equations. In a
posthumous work published in 1615 Vieta dealt with the elements of the theory
of equations, and in particular explained how the coefficients in an
algebraical equation involving one unknown quantity could be expressed as
functions of the roots. Similar results are found in the Algebra by Thomas
Harriot of London (1560-1621), which was first printed in 1631. It is more
analytical than any Algebra that preceded
Vieta’s
results were extended by Albert Girard (1595-1632), a Dutch mathematician. In
1629 Girard published a work which contains the earliest use of brackets, a
geometrical interpretation of the negative sign, the statement that the number
of roots of an algebraical equation is equal to its degree, and the distinct recognition
of imaginary roots. Probably it also implies a knowledge that the first member
of an algebraical equation can be resolved into linear factors. Girard’s investigations
were unknown to most of his contemporaries, and exercised but slight influence on
the development of Mathematics.
Development of Algebra. A far more
influential writer was Descartes (1596-1650). To his famous Discours on
universal science, published at Leyden in 1637, were added three appendices on
Optics, Meteors, and Geometry. The last of these, to which we shall refer again
when dealing with Analytical Geometry, contains a section on Algebra. It has
affected the language of the subject by fixing the custom of employing the
letters at the beginning of the alphabet to denote known quantities, and those
at the end of the alphabet to denote unknown quantities. Descartes here
introduced the system of indices now in use, though he considered only positive
integral indices: probably this was original on his part, but the suggestion
had been made by previous writers, such as Bombelli, Stevinus, Vieta, Harriot,
and Herigonus, though it had not been generally adopted. The meaning of
negative and fractional indices was first given by John Wallis of Oxford
(1616-1703), in his celebrated Arithmetica Infinitorum,1656. It is doubtful whether
Descartes recognised. that his letters might represent any quantities,
positive or negative, and that it was sufficient to prove a proposition for one
general case. He realised the meaning of negative quantities and used them freely.
Further, he made use of the rule for finding a limit to the number of positive
and of negative roots of an algebraical equation, which is still known by his
name, and introduced the method of indeterminate coefficients for the solution
of equations.
Elementary
Trigonometry was also worked out with tolerable completeness, partly by Vieta,
and partly by Girard, while the name of Napier is associated with some of the
fundamental properties of spherical triangles.
In Geometry
new methods of considerable power were introduced at this time. One of these
was due to Gerard Desargues (1593-1662) who in 1639 published a work containing
the fundamental theorems on involution, homology, poles and polars, and
perspective. Desargues gave lectures, in Paris from 1626 for a few years, and
it is believed exercised great influence on Descartes, Pascal, and other French
mathematicians of the time. But his system of Projective Geometry fell into
comparative
Development of Geometry. The Cartesian
system of Analytical Geometry was expounded by Descartes in the tract on
Geometry appended to his Discours. In effect, Descartes asserted that the
position of a point in a plane could be completely determined if its distances,
say x and y, from two fixed lines drawn at right angles in the plane were
given, with the convention familiar to us as to the interpretation of positive
and negative values; and that, though an equation f(x, y) = 0 was
indeterminate and could be satisfied by an infinite number of values of x and y, yet these values of x and y determined the coordinates of a number of
points which form a curve, of which the equation f(x, y) = 0 expressed some
geometrical property—that is, a property true of the curve at every point on
it. Descartes asserted that a point in space could be similarly determined by
three coordinates; but he confined his attention to plane curves.
It was at
once seen that, in order to investigate the properties of a curve, it was
sufficient to select, as a definition, any characteristic geometrical property,
and to express it by means of an equation between the (current) coordinates of
any point on the curve—that is, to translate the definition into the language
of Analytical Geometry. The equation so obtained contains implicitly every
property of the curve, and any particular property can be deduced from it by
ordinary Algebra without troubling about the Geometry of the figure. This may
have been dimly recognised or foreshadowed by earlier writers; but Descartes
went further and pointed out the very important facts, that two or more curves
can be referred to one and the same system of coordinates, and that the points
in which two curves intersect can be determined by finding the roots common to
their two equations.
We need not
describe the details of Descartes’ work. His great reputation ensured
appreciation of his investigations, and an edition of this tract with notes by
Beaune and a commentary by van Schooten, issued in 1659, became a standard
text-book; henceforth the subject was familiar to mathematicians. It should
perhaps be added that it is probable that the principles of Analytical Geometry
had been worked out independently by Pierre de Fermat of Toulouse (1601-65) at
least as early as by Descartes; but, as they were not then published, we need
not discuss this point further.
More than one
writer at this time concerned himself with the division of quantities, such as
areas and volumes, into infinitesimals, and with the summation of such
infinitesimals, thus escaping the long and tedious method of exhaustions used
by the Greeks. In this connexion we should in particular mention the names of
Kepler, Cavalieri, and somewhat later that of Fermat. The most important
exposition of the subject was that given by Wallis in 1656, in which he applied
it to determine the quadrature of a curve. These investigations
foreshadowed the introduction of the infinitesimal calculus by Newton and
Leibniz towards the end of the seventeenth century.
Before
leaving the subject of Pure Mathematics, we must in passing mention the theory
of numbers and that of probabilities. The former, under the stimulus of the
writings of one of the greatest mathematicians, Fermat, attracted considerable
attention. The latter was created by Pascal (1623-62) and Fermat.
Pure
Mathematics are a useful if not necessary instrument of research; but the
general reader takes more interest in the history of their application than in
their own—in results rather than in methods. We turn now to consider the
development of applied science during this period.
Development of Mechanics. As before, we
begin with Mechanics. Simon Stevinus of Bruges (1548-1620), who died at the
Hague, used, though he did not explicitly enunciate, the triangle of forces,
which he treated as the fundamental theorem of Statics (1586). A similar
position was taken up by Galileo (1564-1642). A year or two later the
last-mentioned mathematician laid the foundations of the science of Dynamics.
In 1589, when professor at Pisa, he made experiments from the leaning tower
there on the rate at which bodies of different weights would fall. It was at
once apparent that the generally accepted assertion of Aristotle was incorrect,
and that, save for the resistance of the air, all bodies fell at the same rate,
and through distances proportional to the square of the time which had elapsed
from the instant when they were allowed to drop. Of this Galileo gave a public
demonstration; but, though his Aristotelian colleagues could not explain the
result, many of them preferred to assert that there must be some mistake
rather than admit the possibility that Aristotle was wrong. The ridicule cast
by Galileo on this argument caused friction, and in 1591 he was obliged to
resign his chair. His writings at this time show that he had already formed
correct ideas of momentum and centrifugal force. He had proved that the path of
a projectile was a parabola, and was aware that the pendulum was isochronous.
The last fact he discovered by noticing that the great bronze lamp hanging from
the roof of the cathedral at Pisa performed its oscillations, whether large or
small, in equal times. He nowhere stated the laws of motion in a definite form;
but probably he was acquainted generally with the principles of the first two
laws as enunciated by Newton. His astronomical work was accomplished shortly
after he left Pisa, and to this reference is made below. Towards the end of his
life he again took up the subject of Mechanics, and a book by him, published in
1638, has been described as a masterpiece of popular exposition of its
principles. In it he describes his pendulum experiments, and the theory of
impact. A year or two later he invented a pendulum clock, though the fact was
not generally known at the time. Mechanics were discussed by Descartes in
1644; but he did not substantially advance the theory. The correct
Development of Astronomy.Galileo's astronomical work. The most
striking achievement of this period in the eyes of an ordinary citizen of the
time was the establishment of the Copernican system of Astronomy. We have
already alluded to the publication by Copernicus of his hypothesis. The next
stage in its development was due to Kepler (1571-1630). He served under Tycho
Brahe, one of the most skilful observers of his time, and making use of Brahe’s
observations succeeded, after many and laborious efforts, in reducing the
planetary motions to three comparatively simple laws. The first two were
published in 1609, and stated that the planets describe ellipses round the sun,
the sun being in a focus; and that the line joining the sun to any planet
sweeps over equal areas in equal times. The third was published in 1619, and
stated that the squares of the periodic times of the planets are proportional
to the cubes of the major axes of their orbits. The laws were deduced from
observations on the motions of Mars and the earth, and were extended by analogy
to the other planets. These laws pointed to the fact that the sun and not the
earth should be regarded as the centre of the solar system. We may add that
Kepler attempted to explain why these motions took place by a hypothesis which
is somewhat like Descartes’ theory of vortices described below. He also
suggested that the tides were due to the attraction of the moon.
The invention
of the telescope at the beginning of the seventeenth century facilitated
observations of the nearer planets. The earliest discoveries with its aid were
made by Galileo. In the spring of 1609 he heard that an optician of Middelburg
had made a tube contairing lenses which served to magnify objects seen through
it. This gave him the clue, and he constructed a telescope of the kind which
still bears his name, and of which an ordinary opera-glass is an example. The
instrument magnified three diameters—that is, made objects appear as though only
at one-third of their real distance. Encouraged by this success, he constructed
a larger instrument of thirty-two diameters’ power which magnified an object
more than a thousand times. Intense interest was excited by these discoveries.
He placed one of his instruments on a church tower at Venice, and, to the
amazement of the merchants, showed them their ships approaching the harbour
hours before any details could be detected by the eye. Turning his instrument
to the heavens, he saw the lunar mountains, Jupiter’s satellites, the phases of
Venus, Saturn’s ring, and the solar spots; from the motion of the latter he
concluded that the sun rotates on its axis. In 1611, he exhibited in the garden
of the Quirinal the wonders of the new worlds revealed by the telescope.
At first
honours were showered upon him; but theological opposition arose so soon as it
was realised that the observations tended to confirm
The dramatic
persecution of Galileo has concentrated public attention on his work. But it
should be noted that other mathematicians were also using the telescope to good
advantage. In England Harriot had a large telescope through which he observed
the satellites of Jupiter in 1610. Kepler also made various observations, and
suggested that the eye-glass should be a convex lens. The transit of Venus was
observed by Jeremiah Horrocks in Lancashire in 1639.
The
acceptance of the Copernican system brought into prominence the problem of
explaining the cause of the planetary motions. Descartes suggested in his Principia that space was filled with ether moving in whirlpools of varying sizes
and under varying physical conditions. He supposed that the sun was the centre
of a vortex in which the planets are swept round. Each planet was again the
centre of another vortex in which its moons are swept round. He explained
gravity by the action of these vortices, and suggested that smaller
vortices round the molecules of bodies would account for cohesion. This
suggestion was widely accepted, and is interesting as a genuine attempt to
explain the phenomena of the universe by mechanical laws. But Descartes’ assumptions
were arbitrary, and unsupported by investigation. It is not difficult to prove
that on his hypothesis the sun would be in the centre of these ellipses and
not at a focus (as Kepler had shown was the case), and that the weight of a
body at every place on the surface of the earth except the equator would act in
a direction which was not vertical. It will be sufficient here to say that
Newton considered the theory in detail, and showed that its consequences are
not only inconsistent with each of Kepler’s laws and with the fundamental laws
of Mechanics, but also at variance with the laws of nature assumed by
Descartes.
Development of Physics. The invention
of the telescope and the almost simultaneous invention
The view that
the velocity of light was finite, so boldly assumed by Fermat, had originated
in the seventeenth century. Galileo made experiments on the subject, but was
unable to arrive at a definite result, though he and the leading physicists
seem to have supposed that the view was correct. It was not until 1676 that it
was proved. This was done by Olaus Romer (1644-1710), a young Dane then living
in Paris, by observations of the eclipses of Jupiter’s moons. The theories of physical
optics current at this time will be considered later.
Hydrostatics
also received considerable attention during the earlier years of the
seventeenth century. Here too the earliest experiments seem to have been made
by Galileo, who showed that the air has weight, estimated its pressure by the
height of the water column it could sustain, and definitely refuted the
Aristotelian view that a vacuum could not exist. He also described his
experiments on various physical subjects, notably on fluids. These investigations
fairly entitle him to be termed the founder of modern Physics.
Galileo’s
work was carried on by his pupil Evangelista Torricelli of Florence (1608-47)
who constructed a barometer. The description given of it was vague, but it
suggested ideas to Pascal which led not only to his barometric experiments, but
to proofs of the more elementary propositions relating to the pressure exerted
by fluids. Later investigations were facilitated by the invention of the
air-pump by Otto von Guericke of Magdeburg (1602-86). In England the subject
was taken up by Robert Boyle (1627-91). His name is associated with the law
which be discovered that the pressure exercised by a given quantity of a gas is
proportional to its density. The law was rediscovered independently fourteen
years later by Edme Mariotte (1620-81) in France, who did a great deal to
popularise physical investigations in France, and was one of the founders of
the French Académie des Sciences. The beginnings of experimental investigations
on Heat were also indebted to the labours of Galileo, who invented a
thermometer, though of an imperfect type; but it was nearly a century later
before the subject was taken up systematically.
Another
branch of Physics originated at this time was that connected with Electricity
and Magnetism. Although there had been a few previous observations on the
subject by Cardan, Mercator, and Porta, it may be said to have commenced with
the work of William Gilbert (1540-1603), physician in ordinary to Queen
Elizabeth. His experiments were published in 1600.
The necessity
of an experimental foundation for science was in the course of this period
advocated with considerable effect by Francis Bacon (1561-1626) in his Novum
Organum, published in 1620. Here he laid down the principles which should guide
those making experiments in any branch of Physics, and gave rules by which the
results of induction could be tested. Bacon’s book appealed to men of
education, and helped to secure recognition for the proposition that experiment
and observation are necessary preludes to the formation of scientific
theories. For practical purposes, however, it was of but little use. Bacon
thought that investigations could be made by rule, and did not realise that the
creation of scientific hypotheses was impossible without imagination. The book
had more influence among philosophers and men of letters than among scientific
students.
Towards the
middle of the seventeenth century the progress of scientific learning received
a great stimulus, especially in England and France, from the foundation of
academies or societies, created for the purpose of encouraging scientific
investigations and providing a common meeting-place where those engaged in it
could interchange ideas. Some account of these associations and of the part
which they played in the history of science will be found in another section of
this chapter.
Invention of the Infinitesimal Calculus. Newton and Leibniz. Great as was
the advance in knowledge made during the first half of the seventeenth century,
that from 1660 to 1730 was even more marked.
In the branches
of Pure Mathematics previously mentioned it will suffice to say that Algebra
and Trigonometry became more analytical, and that Newton’s discovery of the
binomial theorem and his work on the theory of equations were especially
notable. Towards the end of the period the extension of Trigonometry to
imaginary quantities was made by Abraham Demoivre of London (1667-1754) whose
name is associated with the fundamental theorem on the subject. No new
developments of Pure Geometry took place during this period; but the classical
methods were applied to various problems with extraordinary ingenuity by Newton
in the first book of the Principia. The methods of Analytical Geometry were
also developed and it became a familiar tool in the hands of mathematicians.
A novel and
potent instrument of research was developed in the infinitesimal calculus. This
method of analysis, expressed in the notation of fluxions and fluents, was used
by Newton (1642-1727) in or before 1666; but no account of it was published
until 1692, though its
The idea of a
fluxion or differential coefficient, as treated in this period, is simple. When
two quantities—for instance, the radius of a sphere and its volume—are so
related that a change in one causes a change in the other, the one is said to
be a function of the other. The ratio of the rates at which they change is
termed the differential coefficient or fluxion of the one with regard to the
other, and the process by which this ratio is determined is known as
differentiation. Knowing the differential coefficient and one set of
corresponding values of the two quantities, we are able by summation to
determine the relation between them; but often the process is difficult. If
however we can reverse the process of differentiation, we can obtain this
result directly. This process of reversal is termed integration, and was first
employed by Newton and Leibniz. It was at once seen that problems connected
with the quadrature of curves, and the determination of volumes (which were
soluble by summation, as had been shown by the employment of indivisibles)
were reducible to integration. In Mechanics also, by integration, velocities
could be deduced from known accelerations, and distances traversed from known
velocities. In short, wherever things change according to known laws, here was
a possible method of finding the relation between them. It is true that, when
we try to express observed phenomena in the language of the calculus, we
usually obtain an equation involving the variables, and their differential
coefficients—and possibly the solution may be beyond our powers. Even so, the
method is often fruitful and its use marked a real advance in thought and
power.
With the
various applications—important though they were —of the calculus to Geometry and
Mechanics we need not concern ourselves, but one application is sufficiently
important to demand a word in passing. This was the discovery in 1712 by Brook
Taylor (1685-1731) of the well-known theorem by which a function of a single
variable can be expanded in powers of it. It was published in 1715, though no
satisfactory proof was given at the time.
The ideas of
the infinitesimal calculus can be expressed either in the notation of fluxions
or in that of differentials. There is no doubt that the differential notation
is due to Leibniz; but an acute controversy arose as to whether the general
idea of the calculus was taken by him from a manuscript by Newton, to which it
was supposed he had had access, or whether it was discovered independently.
During the eighteenth century the prevalent opinion was against Leibniz; but
today the majority of judges think it more likely that the inventions were
independent. The controversy was complicated by bitter personalities. It was natural,
Leibniz was a man of extraordinary versatility; and, in addition to his diplomatic activity, played a prominent part in the literary and philosophical history of his time. Mathematics were not his main interest, and he produced very little mathematical work of importance besides his papers on the calculus; his reputation in this subject rests largely on the attention which he drew to it. In 1686 and 1694 he wrote papers on the principles of the new calculus. In these, his statements of the objects and methods of the infinitesimal calculus, are somewhat obscure, and his attempt to place the subject on a metaphysical basis did not tend to clearness; but the fact that all the results of modern Mathematics are expressed in the language invented by him has proved the best monument of his work. Newton
elaborated the calculus more completely than Leibniz, but his
methods were
buried in note-books inaccessible to all save a few friends;
and the general
adoption of Leibniz’ notation was largely due to the fact
that, through a
text-book published in 1696 by the Marquis de L’Hospital of
Paris, it was at
once made known to all interested in the subject. It was also
regularly used by
Peter Varignon (1654-1722), the most eminent French
mathematician of the time,
and by the brothers James Bernoulli (1654-1705) and John
Bernoulli
(1667-1748)—men of remarkable ability who applied the new
calculus to solve
numerous problems. The Bernoullis were the most prominent
continental teachers
of this period and their influence was exceptionally potent.
The accounts at first
given of Newton’s method of fluxions were less complete; and
more than a generation passed after the production of L’Hospital’s work,
before Colson in 1736,
and Maclaurin in 1742, published systematic expositions of the
fluxioinal
method,
Newton's theory of gravitation. We turn next to
the subject of Mechanics, which was placed on a scientific basis through the
researches of Newton. The investigations by Galileo on the fall of heavy
bodies, and the theory of pendulums, were completed by Huygens (1629-95) in his Horologium Oscillatorium, published at Paris in 1673. In this work
he determined the centrifugal force on a body moving in a circle with uniform
velocity; he also considered the motion of bodies of finite size and not merely
of particles. Newton’s investigations on Mechanics are included in his Principia. It will suffice here to say that he based the subject on three laws
of motion, and he, applied the principles to the statics and dynamics of rigid
bodies and fluids; probably he carried the investigations as far as was possible
The
fundamental principles of Newton’s theory of gravitation seem to have occurred
to him shortly after he had taken his degree at Cambridge. His reasoning at
this time, 1666, appears to have been as follows. He knew that gravity extended
to the tops of the highest hills; and he conjectured that it might extend as
far as the moon, and be the force which retained it in its orbit about the
earth. This hypothesis he verified by the following argument. If a stone is
allowed to fall near the surface of the earth, the attraction of the earth
causes it to move through sixteen feet in one second. Now Newton, as also other
mathematicians, had suspected from Kepler’s law that the attraction of the
earth on a body would be found to decrease as the body was removed further away
from the earth, inversely as the square of the distance from the centre of the
earth. He knew the radius of the earth and the distance of the moon, and
therefore on this hypothesis could find the magnitude of the earth’s attraction
at the distance of the moon. Further, assuming that the moon moved in a circle,
he could calculate the force that was necessary to retain it in its orbit. In
1666, his estimate of the radius of the earth was inaccurate, and, when he made
the calculation, he found that this force was rather greater than the earth’s
attraction on the moon. This discrepancy did not shake his faith in the belief
that gravity extended to the moon and varied inversely as the square of the
distance; but he conjectured that some other force—such, for example, as Descartes’
vortices—acted on the moon as well as gravity.
In 1679
Newton repeated his calculations on the lunar orbit; and, using a correct value
of the radius of the earth, he found the verification of his former hypothesis
was complete. He then proceeded to the general theory of the motion of a
particle under a centripetal force—that is, one directed to a fixed point—and
showed that the vector to the particle would sweep over equal areas in equal
times. He also proved, that, if a particle describes an ellipse under a
centripetal force to a focus, the law must be that of the inverse square of the
distance from the focus; and, conversely, that the orbit of a particle
projected under the influence of such a force would be a conic. In 1684 Hailey
asked Newton what the orbit of a planet would be, if the law of attraction
were that of the inverse square, as was commonly suspected to be approximately
the case. Newton asserted that it was an ellipse, and sent the demonstration
which he had discovered in 1679. Hailey, at once recognising the importance of
the communication, induced Newton to undertake the investigation of the whole
problem of gravitation, and to publish his results.
It would seem
that Newton had long believed that every particle of
The first
book of the Principia is given up to the consideration of the motion of
particles or bodies in free space either in known orbits, or under the action
of known forces, or under their mutual attraction. It is prefaced by an
introduction on the science of Dynamics; it also contains geometrical
investigations of various properties of conic sections. The second book treats of
motion in a resisting medium. The theory of Hydrodynamics was here created, and
it was applied to the phenomena of waves, tides, and acoustics. In the third
book, the theorems of the first are applied to the chief phenomena of the solar
system; and the masses and distances of the planets and (when sufficient data
exist) of their satellites are determined. In particular, the motion of the
moon, with its various inequalities, and the theory of the tides, are worked
out in detail, and as fully as was then possible. Newton also investigated the
theory of comets, showed that they belonged to the solar system, and
illustrated his results by considering certain special comets. The complete
work was published in 1687. A second edition was brought out in 1713 by Roger
Cotes of Cambridge (1682-1716) under Newton’s direction. The demonstrations
throughout are geometrical, but are rendered unnecessarily difficult by their
conciseness, and by the absence of any clue to the method by which they were
obtained. The reason why the arguments were presented in a geometrical form
appears to have been that the infinitesimal calculus was then unknown; and,
had Newton used it to demonstrate results which were in themselves opposed to
the prevalent philosophy of the time, the controversy as to the truth of his
results would have been hampered by a dispute concerning the validity of the
methods used in proving them.
The
publication of the Principia is one of the landmarks in the history of
Mathematics. In it the phenomena of the solar system were shown to be deducible
from laws which experience proved to be true on the earth, and thus it brought
new worlds within the scope of man’s investigations. The conclusions were
generally accepted by the leading thinkers of the time; but a generation or so
had to pass before
It should be
noted that Newton’s conclusions could not have been reached, had not
observational Astronomy also developed. This was largely due to the excellent
work done at Greenwich under Flamsteed (1646-1719), Hailey (1656-1742), and
Bradley (1692-1762), who successively occupied the position of Astronomer
Royal. The last-named explained the aberration of light (1727), and thus
obtained an independent determination of the velocity of light.
Physical Optics. The
achievements of the seventeenth century in Astronomy and Mechanics were so
great that they have thrown some of the other work of the time into comparative
obscurity. The investigations in Physical Optics were, however, of singular
interest. Here again Newton played the leading part. When, in 1669, he was
appointed to a professorship at Cambridge, he at first chose Optics for the
subject of his lectures and researches; and before the end of that year he had
worked out the details of his discovery of the decomposition of a ray of white
light into rays of different colours by means of a prism, from which the
explanation of the phenomenon of the rainbow followed. In consequence of a chapter
of accidents he failed to correct the chromatic aberration of two colours by
means of a couple of prisms; hence he abandoned the hope of making a refracting
telescope which should be achromatic, and, instead, designed a reflecting
telescope, which is of a somewhat different design from those suggested by
James Gregory and N. Cassegrain.
We have
already explained how Newton deduced the motions of the solar system from the
one assumption of universal gravitation. The similar problem in Optics was the possibility
of making a single hypothesis from which all the known optical phenomena could
be deduced. Two plausible theories of this kind had been already suggested. In
one, known as the “corpuscular” or “emission” theory, it is assumed that a
luminous object emits corpuscles which hit or affect the eye. In the other,
known as the wave or undulatory theory, it is assumed that light is caused by a
series of waves in an ether which fills space, the waves being set in motion by
pulsations of the luminous body. It would seem that at one time Newton deemed
the latter the more probable hypothesis; but, though he could thus account for
the phenomena of reflexion, refraction, and colours, it failed (as then
propounded) to explain the rectilinear propagation of light; and this he
considered fatal to its claims. He accordingly turned to the corpuscular
theory, and from it deduced the phenomena of reflexion, refraction, colours,
and diffraction. To do this, however, he was obliged to add a somewhat
artificial rider, that the corpuscles had alternating fits of easy
The wave
theory had been roughly outlined in 1665 by Robert Hooke. It was elaborated in
a paper by Huygens in 1678, and expounded at greater length in his Traité de
la Lumière, published in 1690. From it Huygens deduced the laws of
reflexion, refraction, and double refraction. He was acquainted with the
phenomena of polarisation; but he was unable to explain them since he assumed
the vibrations in the ether to be longitudinal. It was not until the nineteenth
century, when Fresnel worked out the theory on the hypothesis that the vibrations
were transverse, that it was put on a satisfactory basis. Huygens was among the
most illustrious mathematicians of his age, and the wave theory may be fairly
deemed to be due to him. The immense reputation of Newton induced a general
acceptance at the time of the corpuscular theory as enunciated by him—an
unfortunate result of his extraordinary achievements, and the more curious
hecause his writings show that on some grounds he deemed the wave theory the
more probable. In science, as in other subjects, too much reliance should not
be placed on individual authority.
The theory of
Hydrodynamics, including therein Sound and vibrations of fluids, may be said to
have been created by Newton in the second book of his Principia. He determined
experimentally the velocity of sound in air and other media. The difficulties
of mathematical analysis involved are great, and he was not able to carry the
theory very far. In connexion with the theory of Sound, may also be mentioned
the names of Brook Taylor, who gave the theory of the transverse vibrations of
strings, Joseph Sauveur (1653-1715), and Francis Hauksbee (1650-1713).
As to other
physical subjects, we may say that in all of them, at this time, there was
intelligent observation and experiment. In particular the subject oh Heat was
attacked on the right lines by Boyle, Hooke, Newton and others, though the
experimental data available were but slight. So, too, as to the work of the
time in Electricity, which attracted the attention of Boyle, Hailey, Newton,
Picard, and Hauksbee.
The death of
Newton and the separation of the British school of mathematicians from their
continental contemporaries may be taken as marking the close of an epoch. At
the beginning of the seventeenth century Mathematics were only just breaking free
from their medieval trammels, and Physics in the modern sense were
non-existent. In but little more than a century Mathematics had been developed
into an instrument of great power; the value of the calculus had been
recognised, and the foundations of modern analysis laid; the theories of
Mechanics and gravitation had been established; and the problems of Physical
Optics had been subjected to mathematical processes. In this extraordinary
extension of knowledge all the leading nations of Europe had
(2) OTHER BRANCHES OF SCIENCE.
The
seventeenth century may, in a broad way, be spoken of as the period during
which the Natural Sciences—according to our modem lassification of them—Botany,
Zoology, Anatomy, Physiology, Geology, and, we may add Chemistry, took definite
shape, and began to be built up, each in its own way, as an independent branch
of knowledge. The labours of the eighteenth and nineteenth centuries were, in
their turn, largely directed towards carrying forward what had then been begun.
But the impulse which led to this great development is to be found in the
preceding century, or even earlier: in the revolt against the scholastic spirit
which formed so large a part of the Renaissance.
The sciences
in question, though having their birth partly in mere natural curiosity, sprang
largely from the Art of Medicine. The treatment of disease led to enquiry into
the structure and action of the body of man, and this in turn to the study of
animals. The use of herbs as remedies moved men to observe the features and
qualities of plants; and the science of Chemistry, though it began as Alchemy
in the search for the transmutation of metals, and continued to be supported by
the needs of industrial life, was in the main developed by the desire to find
substances which should cure diseases. In the sixteenth century, and long
afterwards, the men who were buildiag up the several natural sciences were to
be found among the teachers of the medical schools.
Hence it is
not wonderful that the first great triumph of the revolt against the scholastic
spirit,, though it was won in a limited and strictly medical branch of
knowledge, namely Human Anatomy, served as a bright example to nearly all the
branches of natural knowledge, and exerted a powerful influence upon them.
In Human
Anatomy the scholastic spirit remaned supreme up to the middle of the
sixteenth century. The far-reaching, almost inspired labours of Galen had in
quite early times produced a system of doctrines touching the structure and functions
of the body of man so complete and consistent that it seemed to supply all that
was needed to be known; the study of these things came to mean the study of
Galen, the written page was the authority, and enquiry was narrowed to
interpretation. In 1543 Andreas Vesalius (1514-64), a young professor at Padua,
published a book on the structure of the human body, based, not on what Galen
taught, but on what Vesalius had himself seen, and what anybody might
The brilliant
success thus gained by the new method applied to Human Anatomy could not fail
to have an influence on other branches of learning, supported as that influence
soon was by the striking results of the same new method in Mechanics and
Physics. How completely this new method had laid hold of men’s minds is shown
by the brilliant exposition of it given by Francis Bacon (1560-1626). Though
his published works belong to the seventeenth century, the Proficience and
Advancement of Learning appearing in 1605 and the Novum Organum in 1620,
Bacon’s main ideas had come to him in the closing years of the preceding
century. In the two works just mentioned, and in others, some published in his
lifetime, and others at various times after his death, he elaborated in a
formal exposition the principles of the method of investigating nature—the new
method which, as we have just said, was being adopted by enquirers everywhere
in all branches of natural knowledge. He went further: he drew up the
outlines, and laboured to the time of his death to fill in the details, of a
plan for the scientific work of the future, a programme of the steps to be
taken in all branches of science in order to gather in with the least waste of
time and labour, and in the most effective manner, the fruits of scientific
enquiry. He made no notable contribution of his own to the advancement of
natural knowledge; there is no evidence that the men who in his own time and
in the times immediately following were actively and effectively engaged in
advancing natural knowledge were in any special way influenced by his
writings; indeed one of the greatest of these enquirers spoke slightingly of
them. “He philosophises,” said Harvey, “like a Lord Chancellor.” And not only
was no effort made by subsequent inquirers to carry out Bacon’s programme, but
the history of scientific discovery has shown that his forecast of how
scientific work ought to be
In spite of
its success in the case of Anatomy, the new method was slow in laying hold of
Physiology. More than half a century passed before it did so; but, when in 1628
William Harvey (1578-1657), by the publication of his Exercitatio de Motu
Cordis, shattered the Galenic Physiology as completely as Vesalius had put an
end to the Galenic Anatomy, the effects were profound and far-reaching.
According
to
Galen, the crude venous blood, enriched in the liver by the
food brought from
the alimentary canal and endowed with the nutritive qualities
spoken of as the
“natural spirits,” flows from the heart to all parts of the
body along the
veins, and returns back to the heart along the same channels.
Some of this
blood, passing from the right side of the heart to the left by
minute pores in
the septum of the ventricles, invisible to the eye of man,
mixes there with air
sucked in through the lungs by the action of the heart. This
mixture is by the
innate heat of the heart “concocted” into arterial blood,
endowed with “vital spirits” which flows from the heart along the
arteries to all parts of
the body, returning by the same channels. When it reaches the
ventricles of the
brain, the arterial blood, by the help of air drawn in through
the pores of the
ethmoid, or sieve-like, bone, gives rise to “animal spirits”
and, flowing as
a pure spirit along the nerves, carries out sensation and
movement.
Long before
Harvey, Michael Servetus (1511-53), in his Restitutio Christianismi, published
in 1553, but written long before, used words showing that he rejected wholly
the supposed passage of some blood through the septum, as to which Vesalius had
simply hinted his doubts, and, further, that he had grasped the true features
of the pulmonary circulation, the passage of all the blood from the right side
of the heart through the lungs to the left side. The same truth was taught by
Colombus (1516-59), Vesalius’ pupil and successor at Padua; but there are some
reasons for thinking that he had read Servetus’ book. Andreas Caesalpinus
(1519-1603), botanist, physician, and polemic philosopher, more than anatomist
or physiologist, also enunciated views which, at all events, show that he
grasped the truths both of the systemic and pulmonary circulations, the flow to
the tissues along the arteries,
Harvey Thus the
doctrines of Galen had been attacked before Harvey’s time; but how little
effect had been produced by these attacks is shown by the teachings of
Fabricius of Aquapendente (1537-1619), who, at the close of the sixteenth
century, in the chair at Padua once held by Vesalius, was, by the fame of his
learning, drawing students from all parts of the world, among them William Harvey.
Although Fabricius did more than anyone after Vesalius to advance Anatomy, to
the end of his days he taught almost pure Galenic doctrines of the circulation,
ignoring what Servetus and Caesalpinus had written, and refusing to see the
real meaning of his own great discovery of the valves in the veins. It was a
mixed teaching, then, of new Anatomy and old Physiology which Harvey got from
Fabricius at Padua, while he studied there from 1597 to 1602. But he probably
learnt much outside the anatomical theatre; for during those years Galileo
Galilei was working at and teaching the new Mechanics and Physics in Padua. It
was perhaps partly at least through Galileo’s influence that Harvey was led to
apply the experimental method to Physiology, and to “give his mind to
vivisections.”
His first
observations, as happens in many a progress, led him into a slough of despond;
he began to think that “the motion of the heart was only to be comprehended by
God.” But the patient study of that motion in the hearts of many living animals
convinced him that Galen was wrong in regarding the heart as mainly an organ of
suction, and that it was, on the contrary, essentially an organ of propulsion,
inasmuch as its work consisted, not in sucking air from the lungs, but in driving
blood by its contractile power through the body. This new view—dimly, but only
dimly, seen by Caesalpinus —Led Harvey at once to a true conception of the work
of the auricles and ventricles with their respective valves, and thus to the
wholly new idea that all, and not some only, of the contents of the right
ventricle were discharged into the lungs and so found their way to the left
side of the heart. This step led to another. Making observations to determine
the quantity of blood discharged at each beat from the left ventricle, and
noting the frequency of the beats, he saw that the blood driven along the
arteries must find its way somehow into the veins and so return to the right
side of the heart. Thus, by experiments and quantitative observations, working
not after the manner of Fabricius but after that of Galileo, he reached a new
view of the circulation of the blood, “of a motion as it were in a circle.”
And all his further observations confirmed this view, which, once fairly
grasped, rendered intelligible various phenomena of the heart and blood
vessels, as indeed of the body at large, hitherto obscure, and made plain the
uses of those valves of the veins over which Fabricius had stumbled. It is
worthy of notice that Harvey says nothing about the “spirits,” so prominent in
the
Freed, as it
were, by the work of Harvey from the bonds of the Galenic doctrines, Physiology
expanded rapidly in the succeeding years, developing in several more or less
independent directions. Its progress was greatly helped by three things: by the
rapid advance of mechanical and physical learning, by the invention of the
compound microscope, and, somewhat later, by the growth of a serious, no longer
fantastical, Chemistry. Harvey himself, though as we have seen he seems to have
been guided by the methods of the Italian physicists, made little direct use of
their results. He had no microscope to help him, and his unassisted eye failed
to learn how the blood passed from the small visible arteries to the small
visible veins in the lungs and in the rest of the body; he could only say, it
passed “somehow.” There is in his books hardly a word of Chemistry, and, in his
much later treatise on generation, such Chemistry as he makes use of is of the
ancient kind. “He did not care for chemists,” says Aubrey, “and was wont to
speak against them with an undervalue.”
Harvey's successors. His
successors, however, fruitfully availed themselves of these aids. The compound
microscope and the new Mechanics were soon made use of. In 1661, in a letter to
Borelli on the structure of the lungs studied with the help of the compound
microscope, Marcello Malpighi (1628-94) announced his discovery of minute
channels, the capillaries, joining the ends of the pulmonary arteries to the
beginnings of the pulmonary veins. These were more clearly seen by John
Swammerdam (1637-80), and, even still more clearly, in the tail of the tadpole
by Antony Leeuwenhoek (1632-1723); and, in a short time, this closed mode of
junction of arteries and veins was found to obtain all over the body.
Swammerdam, moreover, in 1658, and Leeuwenhoek in 1668, had discovered the red
blood corpuscles, observed also, but at first not understood, by Malpighi.
Richard Lower
(1631-91) and Giovanni Alfonso Borelli (1608-97) applied to the physical
problems of the circulation—such as the work done by the heart, the velocity of
the flow in the blood vessels, and the pressure exerted on the vascular
walls—the new exact mechanical and physical learning in so complete a manner as
to bring the knowledge of the subject very much to the condition in which it
was when, nearly two centuries later, Poisseuille and Weber took up the same
problems again. And Jean Pecquet’s (1624-74) discovery, in 1651, of the
thoracic duct discharging its contents into the veins of the neck, and his
proof that the lacteals, discovered in 1622 by Gaspar Aselli, passed, not—as
Aselli
In the
Galenic doctrines, the use of the air in breathing was to temper the great
innate heat of the heart and to provide for the escape of the “fuliginous
vapours” generated during the formation of the vital spirits. Fabricius, who
making use of the new mechanical learning was able to give a fairly good and
correct account of the mechanics of breathing, still held to the old Galenic
idea as to the use of the inspired air. The acceptance of the Harveian teaching
entailed some change in this old idea, but Harvey himself was silent about it.
The first step towards the truth was taken by Robert Boyle (1627-91), who,
unlike Harvey, had attached himself with zeal to the rising chemical learning.
In his New Experiments Physico-Mechanical touthing the Air (1660), he showed
that in air rarefied by the air-pump flame was extinguished and at the same time
life (the life of a mouse) came to an end; thus proving that the action of the
air in breathing, so far from being a tempering of heat, was on the contrary to
be compared to a favouring of combustion as the source of heat. Then Robert
Hooke (1635-1702) in 1667, in an experiment made before the Royal Society,
showed that an animal, a dog, could be kept alive, in the absence of all
movements of the chest or indeed of the lungs, by artificial respiration. He
thus proved the essential feature of breathing to be the exposure of the venous
blood brought by the pulmonary artery to fresh air, and that the movements of
the chest were merely the means of providing repeated supplies of fresh air.
This important conclusion was followed up by Lower, who in 1669 showed that the
difference between venous and arterial blood, as indicated by the difference in
colour, was not profound, as the Galenic doctrine supposed, but transitory, and
due to the mere exposure of the venous blood to the fresh air, and to the
taking-up by the blood of some of the air during the exposure; thus he was
able, by giving air, to turn the purple venous blood into bright red arterial
blood, and, by keeping air away, to effect the converse change.
Neither Lower
nor Borelli, who had treated very fully of breathing and had also come to the
conclusion that air is taken up by the blood in the lungs, nor, again, Hooke,
refers to the possibility of a part of the air only being taken up. John Mayow
(1643-79), who busied himself much with chemical matters, had in 1688 come to
the conclusion that the air consists in part “of a certain vital, fiery, and in
the highest degree fermentative spirit” which he called spiritus nitro-aereus or igneo-aereus. It is clear that in his spiritus nitro-aereus Mayow had formed
a conception of what more than a hundred years afterwards came to be called
oxygen.
And in a
tract on respiration, besides giving an admirable account of the mechanics of
respiration, he showed that the air which is taken up by the venous blood in
the lungs during its change into arterial blood is not the whole air, but the
nitro-aerial part of it, that is the oxygen. Thus building on the foundation
laid by their countryman Harvey, a small knot of Englishmen constructed almost
the whole edifice of the theory of breathing.
Malpighi One effect of
Harvey’s new teaching was a demand for more exact knowledge of the finer
structure and nature of the parts through which the blood was continually
flowing; for the views of the older anatomists on this matter were very vague:
what was not visible fibre and blood vessels they were content to call parenchyma, and any small soft part they spoke of as a gland. This demand
Malpighi was, with the help of the microscope, one of the first and one of the
most successful to supply. By a series of remarkable researches on the viscera,
he laid the foundation of that knowledge of the tissues which forms so large a
part of modem physiology. Making use of the discoveries of the ducts of
pancreatic and salivary glands by Wirsung, Wharton and Stensen, and the works
of Sylvius on the features of glands, he studied the kidney, the liver and the
spleen. He expounded the structure of the kidney, going far beyond the initial
discovery by Bellini of the uriniferous tubules. He showed that the substance
of the liver was not, as Glisson had taught, a uniform parenchyma disposed
irregularly between the blood vessels, but was arranged in minute masses, which
he called acini, after the fashion of the salivary and other glands; that the
liver was, in fact, a huge secreting gland, secreting bile through the gall
duct. And he proved that the spleen was not a gland at all but a contractile
vascular organ. Thus incidentally, at one stroke, he demolished the old idea of
the liver concocting two kinds of bile, the lighter yellow, and the heavier
black bile, the scum and faex as it were of fermentation, the former being
discharged into the intestine and the latter going to the spleen. He turned his
microscope also to other parts of the body, to the skin, the tongue, the uterus, the brain, homs, hairs, bones, and the scattered lymphatic glands; he
showed that each part had a definite texture or structure, special to itself;
and, though the idea of “the tissues” did not come into use until long
afterwards, he was on its track. He complained that the acini of the liver were
so minute that their finer “structure” could not be laid bare by the very
best microscope. One cannot help fancying that, with a more powerful instrument
at his command, he might have been led to a knowledge of the hepatic cell and
so to the cellular constitution of the organs which he studied. Other observers
also, notably Leeuwenhoek, applied the microscope to the study of the structure
of parts of the body; but none went so far as Malpighi.
Chemistry: Boyle.—Van Helmont.—Sylvius. The progress
of Physiology in another direction is so closely interwoven with
the progress of Chemistry that it will be better to consider the two together.
During the latter part of the sixteenth and earlier part of the seventeenth
century, though the day of alchemy was past, there was great activity in the
preparation of new chemical substances, this was due partly to natural
curiosity, partly to the demand for new remedies and for new industrial
materials. And these preparations were conducted to a very large extent by the
method of exact measurement which in Physics was proving so fruitful. But there
was no corresponding progress in chemical theory; “chemists,” said Boyle, “have
been much more happy in finding experiments than the causes of them, or in
assigning the principles by which they may best be explained.” Chemists
continued to accept the three “elements” or “principles” of Paracelsus, or
rather of Valentine, namely, sulphur, mercury, and salt—that is to say, the
classification of substances into those which were combustible and were lost by
combustion, those which were volatile and recovered after combustion, and
those which remained after combustion. Nicolas Lefevre (d. 1674) and others, it
is true, speaking of “oil” instead of sulphur, of “spirit” instead of mercury,
added to the three active two passive principles —“water” or “phlegm” and
“earth”; but this implied no great change.
Later in the
seventeenth century, Boyle laid the foundations of modem Chemistry by severely
criticising in his Sceptical Chemist (1661) those “principles” or “elements,”
and propounding the pregnant idea, that all matter was made up of minute
“corpuscles” capable of arranging themselves in groups, small and simple, or
large and complex; that each such group constituted a chemical substance; and
that chemical change was a rearrangement of groups, a chemical compound being a
union of the constituents and capable of differing in qualities from either of
them; and he attained to far-seeing views as to the part played by heat in
determining the arrangement of the corpuscles. But his conceptions were slow in
making way.
Two other men
had a much more immediate effect on the chemical learning of the century.
Jean-Baptiste van Helmont (1577-1644), in whom the exact quantitative observer
and experimentalist was strangely joined to the visionary, besides discovering
many new chemical substances, laid hold of some important truths. He introduced
the idea of “gas” as something distinct from either air or vapour, and
recognised as gas sylvestre what we now know as carbonic acid gas. He developed
in detail a doctrine of fermentations, and applied it to Physiology. His
description of the chemical processes of the living body as a series of six “fermentative
concoctions,” by which the dead food is converted into blood, first venous,
then arterial, and subsequently into the living active tissues—though marred by
his spiritualistic ideas and his ignoring all that Harvey had done—contains
much that is interesting.
A very
different man was Francis Sylvius (de La Boé) (1614-72), a zealous exponent of
Harvey’s teaching, and of all the new views in
Meanwhile,
Borelli was in like manner explaining everything from a mechanical-physical
standpoint, teaching, for instance, that digestion in the stomach was a mere
mechanical crushing of the food by muscular action into minutest fragments, and
that secretion was a sifting through the sieve of the secreting organ of
particles whose size and shape allowed them to pass through adaptive minute
pores. Thus he in turn became the founder of the “iatro-physical” school.
The phlogiston theory. Both schools
did much, and the English school previously mentioned perhaps even more, to
advance knowledge; but the close of the century witnessed a remarkable
development of chemical conceptions, which turned biological doctrines aside
from the line which they had seemed to be taking. The exact part played by heat
or fire in chemical actions had from quite early times been the subject of
great discussion, Boyle (as we have seen) having had much to say about it; and
now a wholly new notion was started. Johann Joachim Becher (1635-82) in
attempting to revive Valentine’s old “elements” in the form that all things
consisted of three earths, “terra lapidea, improperly called salt, terra
fluida,
The
phlogiston theory was so powerfully advocated and proved so attractive
that—though it argued burning to be a loss, and though it was thus in direct
contradiction to the teaching of Boyle and Mayow— who showed that certain
things, metals for instance, increased in weight by burning—the theory not only
gained immediate and general acceptance, but also remained dominant during the
whole of the century.
Stahl by his phlogiston theory not only profoundly influenced Chemistry and thus indirectly
Physiology, but also exercised a most powerful effect on all biological enquiry
by his earnest advocacy of spiritualistic conceptions. He put forward and
brilliantly maintained the conception that all the chemical events of the
living body, even though they might superficially resemble them, were at the
bottom wholly different from the chemical changes taking place in the
laboratory, since in the living body all chemical changes were directly
governed by the sensitive soul (anima sensitiva) which pervaded all parts and
presided over all events. The pendulum swung back from the somewhat crude
materialism of Sylvius; in the views of the eighteenth century Stahl’s
“sensitive soul” was dominant, and under the weaker title of “vital force” is
powerful even at the present day.
In the
seventeenth century some at least of the modern doctrines of the nervous system
began also to take shape. In the Galenic teaching the “animal spirits” were
concocted in the ventricles of the brain by a mingling of the vital spirits,
brought by the arterial blood, with air drawn in directly from without through
the pores of the ethmoid bone. Within the several ventricles these animal
spirits carried out the various functions of the soul, which they supplied
with sensations by flowing upwards along the nerves. Flowing downward along the
nerves, they entered the fibres, the tendinous part of a muscle, and, by
swelling these up, brought about enlargement or contraction of the muscle, the
fleshy part of which played a wholly passive part, and so gave rise to movement.
Nicolaus
Stensen was the first to show, in 1664, that the fleshy part of
Nervous Physiology. An important
advance was made by Francis Glisson (1597-1677), who on the one hand introduced
the idea and the word “irritability,” as applied to muscular and other tissues,
to denote the faculty of being irritated—a conception destined to play so
important a part in physiology and pathology, and on the other hand made and
described the experiment which still remains as a classic lecture experiment,
that a muscle in contracting does not displace water, showing that contraction
is a change of form only, not of bulk. In this experiment the old Galenic
teaching received its last and fatal blow.
While this
remarkable progress was taking place in the so to speak lower regions of
Nervous Physiology, there was no corresponding advance in the higher regions.
Solid additions to our knowledge of the anatomy of the brain were, it is true,
furnished by Thomas Willis (1621-66), the chief merit of whose work rumours of
the time however attributed to Richard Lower, who assisted him in it; but, when
we turn to the functions of the brain, we find nothing much beyond fanciful
speculations. Descartes, ignoring Harvey’s work and making use of the old
Galenic doctrines, expounded the body of man, including the nervous system, as
a machine capable of being explained by the new mechanical-physical learning
with the help of various assumptions, as, for instance, that the nerves were
tubes along which the flow of animal spirits was regulated by valves; this body
however, though capable of doing much by itself, especially by what we now call
reflex actions, was governed by the “rational soul” hovering around the
pineal gland. Van Helmont taught the existence of an anima sensitiva motivaque,
which, though residing in the pylorus of the stomach, carried out by means of
the brain and nervous system the psychical work as well as the sensations and
movements of
About all
these higher functions of the nervous system and the nature of the soul the
exact observers Malpighi, Borelli, Lower, Sylvius and the rest were silent.
Only one of these spoke on the subject, and then with a few words, mostly
negative. In a lecture delivered at Paris on the anatomy of the brain (1669),
Stensen, after criticising severely the views of Descartes and of Willis, on
the ground that it is impossible to explain the movements of a machine, so long
as we remain ignorant of the structure of its parts, and after explaining the
great difficulties met with in studying the structure of the brain, anticipated
modem discoveries by the suggestion that its fibres were arranged “according
to some definite pattern, on which doubtless depends the diversity of
sensations and movements.”
Structural Botany and Vegetable Physiology. Partly owing
to the use of herbs as remedies, partly to natural curiosity and the love of
beautiful flowers, the sixteenth century was very active in the recognition and
description of plants. From the middle of the century onwards Botanic Gardens
were established at Padua, Pisa, Bologna, Leyden, and elsewhere; and during the
latter half of the sixteenth and beginning of the seventeenth century a number
of elaborate, sometimes highly illustrated descriptions of plants, often known
as “herbals,” were published by men, many of whose names are in common use as
names of plants, such as Fuchs, Gesner, Dodoens, de L’Écluse (Clusius), de
L’Obel (Lobelius), and Bauhin. These descriptions naturally implied a study of
the organs of plants, and various methods of naming them, as well as attempts
at classification. The most important, perhaps, and one of the earliest of such
classifications was that by Caesalpinus (1583), drawn up however more from an a
priori philosophical than from a direct natural history point of view. A classification
introduced later by Joachim Jung (1587-1657) published after his death in 1678,
as well as one by Robert Morison (1620-83), appear to have been used. John Ray
(1628-1705), who in his Historia Plantarum, published between 1686 and 1704,
proposed an arrangement
These various
descriptive works contained of course many references to, and discussions on,
the structure and uses of the parts of plants; but they were for the most part
fragmentary, and in some cases erroneous. In the latter part of the seventeenth
century a remarkable advance was marked by the almost simultaneous production,
in 1671, of preliminary accounts of the structure of plants by Malpighi and
Nehemiah Grew, followed by the fuller work of Malpighi in 1674, and of Grew in
1682. These works cover very much the same ground and in many cases announce
the same discoveries arrived at independently, though Grew in his later work
had the advantage of knowing what Malpighi had written. The two, at one bound,
brought up the knowledge of the anatomy, and specially the finer anatomy, of
plants, from a mere collection of scattered and more or less dubious
observations to a solid and compact body of exact doctrine. They showed—Malpighi
writing with the greater lucidity and pointedness, and Grew with more copious
details—that the elements of the structure of a plant were woody fibres, spiral
vessels, and the cells of the parenchymatous parts with the addition of the
less general lactiferous vessels. They further showed how these elements were
built up in the stem, with its bark, wood and pith and medullary rays, in the
roots, leaves, flowers, fruits and seeds; and how the elements, forming the
roots, were first gathered up into the stem and then separated again into the
branches, thus establishing the continuity of all parts. They thus laid the
foundation of the Histology of Plants, to which Robert Hooke and Leeuwenhoek
made some slight additions, but which otherwise remained untouched for more
than a hundred years.
In describing
structure, both Malpighi and Grew in their works introduced considerations of
function, the former more happily than the latter. Looking upon the woody
fibres as organs for conducting fluid or sap, the spiral vessels or tracheae,
as he called them, as air passages, and the lactiferous vessels as channels for
special juices, Malpighi was led by the study of the young cotyledons of
germinating seeds (which he recognised as leaves) to the important view, that
the crude sap carried upwards from the roots was in the leaves, under the
influence of the sun’s rays, elaborated into more perfect sap; and that this,
descending again, was carried to growing parts or stored up in various places.
And Ray, who treats of Vegetable Physiology incidentally only, had independently
arrived at the same conclusion. As in his researches on the animal body, so in
his study of plants, Malpighi does not attack the chemical side of the problem
of nutrition; and Grew, who did attempt it, was not very successful. Except for
this want of chemical truth, Malpighi and Grew may be said to have laid some of
the
One other
important advance was made in the seventeenth century. Although from quite
early times botanists had recognised that some plants might be spoken of as
fruit-bearing and female and others as not fruit-bearing and male, and
Theophrastus had. called attention to the fact that the female date-palm only
produces fruit when the dust of the male is shaken over it, the view that the
influence of a male element was necessary for the full development of a female
organ into fruit was rarely expressed, and then in most cases obscurely. Some
botanists, for instance Caesalpinus, held that no such influence was necessary;
and Malpighi in his very careful account of the development of seed and of the
earlier stages of the growth of the embryo refers nowhere to any influence of
the pollen, which he otherwise carefully described; he seems to have regarded
the seed as merely a kind of bud. Grew ascribed some subtle influence to the
anthers, but his account is most obscure; and even Ray, who seems after some
hesitation to have finally accepted the doctrine of sexuality, never attempted
to obtain proof of the matter by experiment. In 1691, however, and more fully
in 1694, Rudolf Jacob Camerarius (1665-1721) gave the direct experimental
proof—namely, by removing them—that the anthers were essential to fertilisation,
and showed by his careful account that he had fully grasped the importance of
his discovery.
Systematic Zoology and Comparative Anatomy. The study of
animals made marked progress in the seventeenth century in two directions,
affording in this respect a parallel to the study of plants. In the preceding
century and even earlier the spirit of the new method of research had led men
to be no longer content with the study of Aristotle’s writings and the fabulous
stories of travellers, but to observe for themselves, to describe the features and
habits of such animals as came within their notice, and even to attempt a
classification. As the zeal for travel, which was one of the marks of the age,
brought back to Europe not only accounts but actual specimens of creatures
hitherto unknown, and collections began to be made in the form of museums, both
private and public, as well as of zoological gardens (the date of the earliest
of these it seems difficult to fix), a body of exact zoological knowledge
gradually grew up, expounded in such works, as those of Conrad Gesner (1516-65)
and of Aldrovandus (1527-1605),
This study of
the Natural History of Animals, pursued, mainly out of natural curiosity, and
not for its use in Medicine or otherwise, continuing to make great progress in
the seventeenth century, found a brilliant expositor in the man of science who
was doing a like service for Botany—namely, John Ray. Francis Willughby
(1635-72), first the pupil, and then the intimate friend of Ray, had studied
animals while Ray was chiefly studying plants, the two carrying out their
studies in close concert; but he died early without having published any
important
The
systematic zoologists paid more attention to external features than to internal
structure; but it was only natural that the enquirers who found the actual
dissection of the human body so fruitful of new truths and new ideas should
turn to the dissection of the bodies of animals; and, indeed, many of the
anatomists, notably Fabricius, following the example of Galen, did, in a more
or less desultory fashion, examine and describe the structure of various
animals. In the middle of the seventeenth century, however, two men took up
this work in a more thorough fashion, being therein greatly assisted by the
introduction of the microscope. Malpighi’s account of the anatomy of the
silk-worm (1669) was the pioneer of exact Comparative Anatomy and Histology in
respect to animals, doing for them what his Anatome Plantarum did for plants.
About the same time, Swammerdam was applying the same methods, in a still more
thorough and extensive way, not only to various kinds of insects in their
several stages of metamorphosis, but to other animals as well, such as the
snail and the frog. A few only of Swammerdam’s results were published in his
lifetime; the greater part did not see the light until long after his death,
when in 1737 Boerhaave published under the title of Biblia Naturae the writings
which he had left behind. These two men, Malpighi and Swammerdam, may be said
to have created the science of Comparative Anatomy. The same century saw,
however, other important works. Leeuwenhoek, applying the microscope in all
directions, discovered spermatozoa, made known infusoria and rotifera, and
studied hydra and aphthis. Malpighi, carrying the study of the formation of the
chick in the egg far beyond the rough attempts of Fabricius, laid the
foundations of Embryology Francesco Redi (1670), in proving that maggots were
not bred out of mere corruption, since they did not appear in rotting flesh if
the access of flies was prevented, not only dealt a heavy blow at the widely
accepted theory of spontaneous generation, but introduced a new and fruitful
method of Experimental Biology. Of less, perhaps, but still great value, were
Redi’s works (1684) on the structure and economy of parasitic animals, and
(1664) on vipers, in which he gave an admirable account of the poison
mechanism, and incidentally showed that the poison was not absorbed by the
alimentary canal. He also wrote on the
Mineralogy. In the
sixteenth century, and even earlier, the new spirit of observation
and enquiry did not fail to turn men’s minds to the phenomena of the earth,
especially as disclosed by mining operations. It led George Bauer (Georgius
Agricola, 1494-1555), who lived near the mines of the Erzgebirge, to a very
extensive study of metals and other minerals, and he may be said to have laid
the foundations of Mineralogy. Among the objects of which he spoke as fossilia he included the remains of extinct animals; but he did not recognise these as
such; he made no distinction between them and minerals possessing definite
forms, and thought that they all arose in the same way—that all were the
products of natural forces.
While
minerals were thus being studied from the mining point of view, it was natural
that the men who had been led to study animals and plants, and especially those
who gathered collections of these and formed museums, should also turn their
attention to minerals, precious stones and fossils. Thus Caesalpinus, Conrad
Gesner, Aldrovandus and others treated of these as well as of plants and
animals. But they, or at least the majority of them, failed to distinguish
between ordinary minerals and the mineralised remains of extinct animals; they
spoke of the latter as “sculptured minerals,” lapides figurati, and regarded
them as lusus naturae, as the products of a mysterious vis plastica or lapidifica. This view, however, was not accepted by all. Even in the fifteenth
and, later, in the sixteenth century both those remarkable men, Leonardo da
Vinci and Bernard Palissy, “the Potter,” (1499-1589), had argued forcibly that
these fossils must be the remains of animals and plants which were once living.
Yet it held its ground in a remarkable manner far on into the seventeenth
century, and did not wholly disappear until the end of that century or even
the beginning of the next. Hence, though many collections of fossil plants and
animals were made, and many specimens carefully described, little use was made
of them to interpret the history of the earth.
In the
seventeenth century the labours of John Woodward (16651772), who made large
collections of fossils and minerals and most carefully studied and described
them, were perhaps the most effective in establishing the truth that fossils
were really the remains of plants and animals which were once alive; and in
this he was vigorously supported later by Jean-Jacques Scheuchzer (1672-1733)
and others. But Woodward and the rest were content with the explanation that
the distribution of these fossils at different places and at different depths
from the surface was
One man only
followed in the path begun by Da Vinci, who had not only contended that fossils
were the remains of once living plants and animals, but had also suggested how
their presence in various places and at various depths could be explained by
the action of water. That singular man, Nicolaus Stensen, in a little tract, De
solido intra solidum, published in 1669, a brief preliminary statement
(intended to be followed by a larger and fuller work which, however, never saw
the light), after showing that fossils were really the remains of plants and
animals, went on to infer from the features of the soil in which they were
embedded, and from the other circumstances of their occurrence, the changes
which had taken place leading to their deposition. The little work was in fact
a remarkable anticipation of modem geological doctrines; but it produced no
lasting effect and was soon forgotten. The seventeenth century passed away
without any advance on the beginning thus made.
Early Academies. The story of
the progress of science in the seventeenth century would not be complete
without a reference to the scientific societies which were tokens of the
scientific activity of the time, and powerfully promoted the advance of
scientific knowledge.
During the
fifteenth century the friends of the new studies began to form, in various
cities of Italy, clubs or societies, the members of which, meeting together
under the protection and very frequently at the house of some great or wealthy
personage, used to discuss and take measures to promote the new ideas which
were stirring them. A society of this kind, founded at Florence by Cosimo de’
Medici, which devoted itself to the study of the writings of Plato, thought to
emphasise its platonic character by calling itself an Accademia; and the name
after a while came to be adopted by similar societies. During the sixteenth and
seventeenth centuries these societies, or Academies, multiplied rapidly; they became
the fashion, so that nearly every large city in Italy had at least one, and the
chief cities several. Most of the Academies busied themselves with letters or
with art; they assumed fantastic names; they were in many cases short-lived,
some of them being put down by the Church, or remaining insignificant.
Towards the
middle of the seventeenth century the progress of scientific learning in its
various branches received a great stimulus, in several European countries, from
the foundation of Academies or
The first
society for the prosecution of physical science was established at Naples in
1560, under the name of Academia Secretorum Naturae, and under the presidency
of Baptista Porta. In the course of the seventeenth century two of the Italian
Academies which devoted themselves to science became famous. At Florence, a
society, begun informally in 1651, under the patronage of Ferdinand II, was
formally established in 1657, under the name of the Accademia del Cimento, by
Prince Leopold, at whose palace it met, and who gave it unstinted help. It
devoted itself mainly to mathematical and physical science; many, if not most,
of the greater scientific men of the time were among its members; it discussed,
devised and carried out experimental researches, and in 1667 published an
account of its labours under the title of Saggi di naturali esperienze fatte
nell Accademia del Cimento. In 1667, however, Leopold’s energies being withdrawn
from it on his being created a Cardinal, and several of its active members,
such as Borelli, having left Florence, the Academy came to an end.
At Rome, at
even an earlier date, in 1603, a similar society was founded by Prince Federigo
Cesi under the name of the Accademia del Lincei, which devoted itself mainly to
the natural sciences. Like its sister at Florence, it authorised publications,
and like its sister it had a short life only, coming to an end in 1630, upon
the early death of its founder. Long afterwards—in 1784—the name was revived in
the present Reale Accademia dei Lincei. An Accademia fisico-matematica was
founded at Rome by Giovanni Giustino Ciampini in 1677. The scientific Academy
at Naples had been suppressed by Philip II, and was succeeded by another
Academy of Sciences in 1695.
In England a
society, similar to the Italian Academies, was established in 1645 at London,
meeting at Gresham College or elsewhere, under the private name of the
“Invisible College.” In 1648 the society was divided, some members continuing
to meet, fitfully owing to the troubles of the time, in London, but most of
them at Oxford. In 1660 the meetings in London were revived with success, and
on July 15, 1662, the society was formally incorporated by charter as the “
Royal Society of London,” a second charter being granted in 1663. It is known
how keen and useful an interest was taken by John Evelyn in the early progress
of the Royal Society; his project of a Mathematical College, like his friend
Abraham Cowley’s Philosophical College, remained, however, unaccomplished.
William Molyneux is regarded as the founder of the Dublin Philosophical Society
(1684). In France, at Paris, a similar society, about the middle of the
seventeenth century, met at the house of Melchisedec Thevenot, a man
distinguished by his travels and his interest in science; it was before this
society that Stensen gave his remarkable lecture on the brain, attacking the
teaching
The Academies
belonging to other European countries were founded at later dates.
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