Chapter IV: Preface (4)

In another quantity of rain-water, exposed for some days to the air, I observed some thousands of them in a drop of water, which were of the smallest sort that I had seen hitherto. And in some time after I observed, besides the animals already noted, a sort of creatures that were eight times as large, of almost a round figure; and as those very small animalcula swam gently among each other, moving as gnats do in the air, so did these larger ones move far more swiftly, tumbling round as it were, and then making a sudden downfall.

In the waters of the river Maese I saw very small creatures of different kinds and colours, and so small, that I could very hardly discern their figures; but the number of them was far less than those found in rain-water. In the water of a very cold well in the autumn, I discovered a very great number of living animals very small, that were exceedingly clear, and a little larger than the smallest I ever saw. In sea-water I observed at first, a little blackish animal, looking as if it had been made up of two globules. This creature had a peculiar motion, resembling the skipping of a flea on white paper, so that it might very well be called a water-flea; but it was far less than the eye of that little animal, which Dr. Swammerdam calls the water-flea. I also discovered little creatures therein that were clear, of the same size with the former animal, but of an oval figure, having a serpentine motion. I further noticed a third sort, which were very slow in their motion; their body was of a mouse colour, clear toward the oval point; and before the head and behind the body there stood out a sharp little point angle-wise. This sort was a little larger. But there was yet a fourth somewhat longer than oval. Yet of all these sorts there were but a few of each. Some days after viewing this water, I saw 100 where before I had seen but one; but these were of another figure, and not only less, but they were also very clear, and of an oblong oval figure, only with this difference, that their heads ended sharper; and although they were a thousand times smaller than a small grain of sand, yet when they lay out of the water in a dry place, they burst in pieces and spread into three or four very little globules, and into some aqueous matter, without any other parts appearing in them.

Having put about one-third of an ounce of whole pepper in water, and it having lain about three weeks in the water, to which I had twice added some snow-water, the other water being in great part exhaled; I discerned in it with great surprise an incredible number of little animals, of divers kinds, and among the rest, some that were three or four times as long as broad; but their whole thickness did not much exceed the hair of a louse. They had a very pretty motion, often tumbling about and sideways; and when the water was let to run off from them, they turned round like a top; at first their body changed into an oval, and afterwards, when the circular motion ceased, they returned to their former length. The second sort of creatures discovered in this water, were of a perfect oval figure, and they had no less pleasing or nimble a motion than the former; and these were in far greater numbers. There was a third sort, which exceeded the two former in number, and these had tails like those I had formerly observed in rain-water. The fourth sort, which moved through the three former sorts, were incredibly small, so that I judged, that if 100 of them lay one by another, they would not equal the length of a grain of coarse sand; and according to this estimate, 1,000,000 of them could not equal the dimensions of a grain of such coarse sand. There was discovered a fifth sort, which had near the thickness of the former, but almost twice the length.

In snow-water, which had been about three years in a glass bottle well stopped, I could discover no living creatures; and having poured some of it into a porcelain tea-cup, and put therein half an ounce of whole pepper, after some days I observed some animalcula, and those exceedingly small ones, whose body seemed to me twice as long as broad, but they moved very slowly, and often circularly. I observed also a vast multitude of oval-figured animalcula, to the number of 8,000 in a single drop.

FOOTNOTES:

[Footnote 10: From the _Transactions of the Royal Society of London_.]

IX

SIR ISAAC NEWTON

1642-1727

_Sir Isaac Newton, whose researches in light, gravitation, and mathematics are outstanding in the history of modern science, was born in Woolsthorpe, Lincolnshire, December 25, 1642. He was the son of an English farmer who died before Newton was born. His early education was interrupted by his mother’s poverty, but his ingenuity in making mechanical toys soon provided a means whereby he was enabled to return to school. He entered Cambridge University in 1661 and took his degree in 1665; two years later he was made a fellow of the university, and in 1669 became professor of mathematics._

_In 1665 he discovered his method of fluxions, not greatly unlike Leibnitz’s Differential Calculus. In 1672 he was elected a fellow of the Royal Society and shortly afterwards sent them a paper describing how he had broken up light by means of a prism, demonstrating by that means the compound nature of the sun’s rays._

_In 1687 elaborated his theory of gravitation in “Philosophiæ Naturalis Principia Mathematica.” This was the result of his reflections and researches dating from 1666, when he attempted to explain the moon’s motion by the hypothesis of the assumed influence of gravitation. In the meantime, through the use of telescopic instruments, French geographers had tested the spherical shape of the earth and had made a new and more accurate triangulation. Using the data which they supplied, Newton perceived that these data agreed with his theory that the force varied inversely as the square of the distance. Overcome with the emotion incident to the solution of a great problem, he begged a friend to complete his calculations, with the result that the new astronomy begun by Copernicus, and continued by Brahe, Kepler, and Galileo, was formulated and mathematically interpreted by a single mechanical principle._

_Although he later made some chemical investigations, his papers were accidentally destroyed, and it is said that he never recovered from the shock of losing them. In 1695 he was made warden, and in 1699 promoted to the mastership of the mint, which office he retained at a munificent salary until his death on March 20, 1727._

THE THEORY OF GRAVITATION[11]

BOOK III. PROPOSITION V. THEOREM V. SCHOLIUM

The force which retains the celestial bodies in their orbits has been hitherto called centripetal force; but it being now made plain that it can be no other than a gravitating force, we shall hereafter call it gravity. For the cause of that centripetal force which retains the moon in its orbit will extend itself to all the planets.