There are two theories on this subject among the moderns. Harvey,
Stenon, Graaf, Redi, and other celebrated physicians, maintain that all
animals are oviparous, and spring from eggs, which in the animal kingdom
are what seed is in the vegetable. Hartsoëker and Lewenhoek are of a
different opinion, and maintain that all animals spring by metamorphosis
from little animals of extreme minuteness.
The first of these systems is merely a revival of that taught by
Empedocles, as cited by Plutarch and Galen, and next to him Hippocrates,
Aristotle, and Macrobius. The other system, that of animalcula or
spermatic vermiculi, is but a revival of the opinions of Democritus and
other ancients.
Hippocrates, founding himself upon a principle universally received by
antiquity that nothing arises from nothing, advanced that nothing in
nature absolutely perished; that nothing, taking it altogether, was
produced anew; nothing born, but what had a prior existence; that what
we call birth, is only such an enlargement as brings from darkness to
light, or renders visible, those small animalcula which were before
imperceptible. He maintains that every thing increases as much as it
can, from the lowest to the highest degree of magnitude. These
principles he afterwards applies to generation, and declares that the
larger sizes arise out of the lesser; that all the parts successively
expand themselves, and grow and increase proportionally in the same
series of time; that none of them in reality takes the start of another,
so as to be quicker or slower in growth; but that those which are
naturally larger sooner appear to the eye, than those which are smaller,
though they by no means preceded them in birth or existence.
_Polypi._--The multiplicity of animation of which the polypus is
capable, supposed to have been discovered by the moderns, was known to
the ancients. There are passages of Aristotle and St. Augustine, wherein
they speak of it as a thing which they knew from their own experience.
The latter, in his book entitled “De Quantitate Animæ,” relates, that
one of his friends performed the experiment before him of cutting a
polypus in two; and that immediately the separated parts betook
themselves to flight, moving with precipitation, the one one way, and
the other another. Aristotle, speaking of insects with many feet, says,
that there are of these animals or insects, as well as of plants and
trees, that propagate themselves by shoots: and as what were but the
parts of a tree before, become thus distinct and separate trees; so in
cutting one of these animals, says Aristotle, the pieces which before
composed altogether but one animal, become all of a sudden so many
different individuals. He adds, that the animating principle in these
insects is in effect but one, though multiplied in its powers, as it is
in plants.
_The Sexual System of Plants._
Vivunt in Venerem frondes, omnesque vicissim
Felix arbor amat, nutant ad mutua palmæ
Fœdera, populeo suspirat populus ictu,
Et platani platanis, alnoque assibilat alnus.
_Claudian. de Nuptiis Honorii et Mariæ._
Claudian’s verses have been thus familiarly Englished:--“The tender
boughs live together in love, and the happy trees pass their time
entirely in mutual embraces. Palms by consent salute and nod to each
other; the poplar, smitten with the poplar, sighs; whilst planes and
alders express their affection in the melody of whispers.” This allusion
to the “Loves of the Plants” was not a mere imagination of the old poet:
their sexual difference was known to the old philosophers.
“Naturalists,” says Pliny, “admit the distinction of sex not only in
trees, but in herbs, and in all plants.”
ASTRONOMY--MATHEMATICS--MECHANICS--OPTICS, &c.
_The Vibration of the Pendulum_ was employed, for the purpose it is
still applied to, by the ancient Arabians, long before the epoch usually
assigned to its first discovery. A learned gentleman at Oxford, who
carefully examined the Arabian manuscripts in the library of that
university, says, “The advantages recommending the study of astronomy to
the people of the East were many.” He speaks of “the serenity of their
weather; the largeness and correctness of the instruments they made use
of much exceeding what the moderns would be willing to believe; the
multitude of their observations and writings being six times more than
what has been composed by Greeks and Latins; and of the number of
powerful princes who, in a manner becoming their own magnificence, aided
them with protection.” He affirms, that it is easy “to show in how many
respects the Arabian astronomers detected the deficiency of Ptolemy, and
the pains they took to correct him; how carefully they measured time by
water-clocks, sand-glasses, immense solar dials, and even by _the
vibrations of the pendulum_; and with what assiduity and accuracy they
conducted themselves in those nice attempts, which do so much honour to
human genius--the taking the distances of the stars, and the measure of
the earth.”
_Refraction of Light._--According to Roger Bacon, Ptolemy, the great
philosopher and geometrician, gave the same explanation of this
phenomenon, which Descartes has done since; for he says, that “a ray,
passing from a more rare into a more dense medium, becomes more
perpendicular.” Ptolemy wrote a treatise on optics whence Alhazen seems
to have drawn whatever is estimable in what he advances about the
refraction of light, astronomical refraction, and the cause of the
extraordinary size of planets when they appear on the horizon. Ptolemy,
and after him Alhazen, said, that “when a ray of light passes from a
more rare into a more dense medium, it changes its direction when it
arrives upon the surface of the latter, describing a line which
intersects the angle made by that of its first direction, and a
perpendicular falling upon it from the more dense medium.” Bacon adds,
after Ptolemy, that “the angle formed by the coincidence of those two
lines is not always equally divided by the refracted ray; because in
proportion to the greater or less density of the medium, the ray is more
or less refracted, or obliged to decline from its first direction.” Sir
Isaac Newton subsequently deducing the cause of refraction, from the
attraction made upon the ray of light by the bodies surrounding it,
says, “that mediums are more or less attractive in proportion to their
density.”
_Astronomic Refraction._--Ptolemy, acquainted with the principle of the
refraction of light, could not fail to conclude that this was the cause
of the appearance of planets upon the horizon before they came there.
Hence he accounted for those appearances from the difference there was
between the medium of air, and that of ether which lay beyond it; so
that the rays of light coming from the planet, and entering into the
denser medium of our atmosphere, must of course be so attracted as to
change their direction, and by that means bring the star to our view,
before it really come upon the horizon.
_Why Stars appear largest upon the Horizon_ is attempted to be accounted
for by Roger Bacon. He says it may proceed from this, that the rays
coming from the star are made to diverge from each other, not only by
passing from the rare medium of ether into the denser one of our
surrounding air, but also by the interposition of clouds and vapours
arising out of the earth, which repeat the refraction and augment the
dispersion of the rays, whereby the object must needs be magnified to
our eye. He afterwards adds, that there has been assigned by Ptolemy and
Alhazen another more reasonable cause. These authors thought that the
reason of a star’s appearing larger at its rising or setting than when
viewed over head arose from this, that when the star is over head there
are no immediate objects perceived between it and us, so that we judge
it nearer to us, and are not surprised at its littleness; but when a
star is viewed on the horizon, it lies then so low that all we can see
upon earth interposes between it and us, which making it appear at a
greater distance, we are surprised at observing it so large, or rather
imagine it larger than it is. For the same reason the sun and moon, when
appearing upon the horizon, seem to be at a greater distance, by reason
of the interposition of those objects which are upon the surface of our
earth, than when they are over head; and consequently there will arise
in our minds an idea of their largeness, augmented by that of their
distance, and this of course must make them appear larger to us, when
viewed on the horizon, than when seen in the zenith.
_Perspective of the Ancients._--Most of the learned deny the ancients
the advantage of having known the rules of perspective, or of having put
them in practice, although Vitruvius makes mention of the principles of
Democritus and Anaxagoras respecting that science, in a manner that
plainly shows they were not ignorant of them. “Anaxagoras and
Democritus,” says he, “were instructed by Agatarchus, the disciple of
Eschylus. They both of them taught the rules of drawing, so as to
imitate from any point of view the prospect that lay in sight, by making
the lines in their draught, issuing from the point of view there,
exactly resemble the radiation of those in nature; insomuch, that
however ignorant any one might be of the rules whereby this was
performed, yet they could not but know at sight the edifices, and other
prospects which offered themselves in the perspective scenes they drew
for the decoration of the theatre, where, though all the objects were
represented on a plain surface, yet they swelled out, or retired from
the sight, just as objects do endowed with all dimensions.” Again he
says, that the painter Apatarius drew a scene for the theatre at
Tralles, “which was wonderfully pleasing to the eye, on account that the
artist had so well managed the lights and shades, that the architecture
appeared in reality to have all its projections.” Pliny says, that
Pamphilus, who was an excellent painter, applied himself much to the
study of geometry, and maintained that “without its aid it was
impossible ever to arrive at perfection in that art.” Pliny elsewhere
says, that Apelles fell short of Asclepiodorus in “the art of laying
down distances in his paintings.” Lucian, in his Dialogue of Zeuxis,
speaks of the effects of perspective in pictures, and Philostratus, in
his preface to his Drawings, or History of Painting, makes it appear
that he knew this science; and in his account of Menoetius’s picture of
the siege of Thebes, describes the happy effects of perspective when
studied with care.
_Optical Problem._--Aristotle was the first who proposed the famous
problem respecting the roundness of that image of the sun, which is
formed by his rays passing through a small puncture, even though the
hole itself be square or triangular. “Why is it,” inquires Aristotle,
“that the sun, in passing through a square puncture, forms itself into
an orbicular, and not into a rectilinear figure, as when it shines
through a grate? Is it not because the efflux of its rays, through the
puncture, converges it into a cone, whose base is the luminous circle?”
_Squaring the Circle._--If there remain any hope of solving this problem
it is founded on that discovery of Hippocrates of Chios, called the
squaring of the _Lunulæ_, which is said to have first put him in heart,
they say, to attempt the squaring of the circle. This Hippocrates must
not be confounded with the father of medicine, who was of the isle of
Cos. He who is spoken of here was a famous geometrician, and lived about
five hundred years before Jesus Christ.
Anaxagoras appears to have been the first who dared this enterprise, and
it was when he was in prison at Athens. Plutarch says positively that he
achieved it; but this must be looked upon only as a general expression.
Aristotle in many places mentions the efforts of the Pythagoreans Bryson
and Antiphon, who likewise flattered themselves with having found out
the square of the circle. Aristophanes jeers the learned of his time for
attempting to resolve this problem. One of the nearest approximations to
the solution of this problem is that of Archimedes. He found the
proportion of the diameter to the circumference to be as 7 to 22, or
somewhat between 21 and 22; and it is in making use of Archimedes’s
method, that Wallis lays down rules for attaining nearly the square of
the circle; yet they bring us not fully up to it, how far soever we
advance. Archimedes contented himself with what he had in view, which
was to find out a proportion that would serve all the purposes of
ordinary practice. What he neglected to do, by extended approximations
was afterwards performed by Apollonius, and by Philo of Gadare, who
lived in the third century.
_The Squaring of the Parabola_ is one of the geometrical discoveries
which has done most honour to Archimedes. It is remarked to have been
the first instance of the reducing a curve figure exactly into a
square, unless we admit of Hippocrates’s squaring the _lunulæ_ to have
been of this sort.
_The Burning Glasses, employed by Archimedes_ to set fire to the Roman
fleet at the siege of Syracuse, Kepler, Naudéus, and Descartes have
treated as fabulous, though attested by Diodorus Siculus, Lucian, Dion,
Zonaras, Galen, Anthemius, Eustathius, Tzetzes, and other eminent
authors. Some have pretended to demonstrate by the rules of catoptrics
the impossibility of it; but Kircher, attentively observing the
description which Tzetzes gives of the burning glasses of Archimedes,
resolved upon an experiment; and having, by means of a number of plain
mirrors, collected the sun’s rays into one focus, he by an increased
number of mirrors produced the most intense degree of solar heat.
Tzetzes says, that “Archimedes set fire to Marcellus’s navy, by means of
a burning glass composed of small square mirrors, moving every way upon
hinges; which, when placed in the sun’s rays, directed them upon the
Roman fleet so as to reduce it to ashes at the distance of a bow-shot.”
Buffon’s celebrated burning glass, composed of 168 little plain mirrors,
produced so considerable a heat, as to set wood in flames at the
distance of two hundred and nine feet; melt lead, at that of one hundred
and twenty; and silver, at that of fifty.
Anthemius of Tralles in Lydia, celebrated as an able architect,
sculptor, and mathematician, who in the emperor Justinian’s time built
the church of St. Sophia at Constantinople, wrote a small treatise in
Greek, which is extant only in manuscript, entitled “Mechanical
Paradoxes,” wherein is a chapter respecting burning glasses, with a
complete description of the requisites, which, according to this author,
Archimedes must have possessed to enable him to set fire to the Roman
fleet. His elaborate description demonstrates the possibility of a fact
so well attested in history. Zonaras, speaking of Archimedes’s glasses,
mentions those of Proclus, who, he says, burnt the fleet of Vitellius at
the siege of Constantinople, in imitation of Archimedes, who set fire to
the Roman fleet at the siege of Syracuse. He intimates that the manner
wherein Proclus effected this, was by launching upon the vessels, from
the surface of reflecting mirrors, such a quantity of flame as reduced
them to ashes.
_Refracting Burning Glasses_ were certainly known to the ancients. Pliny
and Lactantius speak of glasses that burnt by refraction. The former
tells of balls or globes of glass, or crystal, which exposed to the sun
transmit a heat sufficient to set fire to cloth, or corrode away the
dead flesh of those patients who stand in need of caustics; and the
latter, after Clemens Alexandrinus, takes notice that fire may be
kindled, by interposing glasses filled with water between the sun and
the object, so as to transmit the rays to it. Aristophanes, in his
comedy of the Clouds, introduces Socrates as examining Strepsiades about
the method he had discovered for getting clear for ever of his debts.
The latter replies, that he thought of making use of a burning glass,
which he had hitherto used in kindling his fire; for, says he, should
they bring a writ against me, I’ll immediately place my glass in the
sun, at some little distance from the writ, and set it a fire.
* * * * *