SEVENTEENTH CENTURY NATURAL SCIENCE

FROM THE CHRISTIANIZATION of Europe in the early Middle Ages to the end of the Thirty Years' War in 1648, the most important subjects for thought were religious. The great minds of Europe mostly spent their efforts on this field. With the discovery of America in 1492 came the first great break in the old order of things. The beginning of modern natural science was made by Copernicus, Galileo, Kepler, and Bacon, and from the middle of the seventeenth century, the growth of the natural sciences has been so rapid that they now constitute by far the greater part of that legacy from generation to generation which we call the world's knowledge.

Before looking at the work itself of the scientists of the seventeenth century, it will give us a better bird's-eye view of the development of the subject to run over the chief advances of the period.

The ideas of Galileo, Kepler and Bacon, whose work made memorable the first of the seventeenth century, have already been noted in a previous volume.

Harvey in 1619 founded physiology by demonstrating the circulation of the blood. Soon afterwards (in 1622) Asellius discovered the lacteal circulation, and in 1649 Olaüs Rüdbeck of Sweden found that these lacteals or lymphatics furnished the thoracic duct, and thus the heart, with the material for new blood. In 1690 Van Leeuwenhoeck strengthened Harvey's theory by discovering the capillary circulation of the blood from the arteries to the veins.

In physics, the advances were many and great. Torricelli invented the barometer (1644) and Pascal (1656) by showing that the

mercury rises to different heights at different altitudes above the earth, proved that it is the weight of the air which causes the rise of the mercury. Guericke in 1650 invented the air pump and in 1672 the first electrical machine. Newton proved the compound nature of light in 1666-71. Roemer in 1676 estimated its velocity by noting the difference in the apparent time of the eclipses of Jupiter's moons, depending upon whether the earth is upon the side of its orbit nearest or farthest from Jupiter. The greatest variation observed was 16 minutes and 36 seconds, or 996 seconds, and the diameter of the earth's orbit was thought to be about 190,000,000 miles. Light would then travel about 190,000 miles in a second. Huyghens took up the question of the nature of light and in 1678 developed his wave theory and his conception of ether as the medium through which light moves. In 1682 Newton worked out his law of gravitation and showed that weight is the result of an attractive force between masses of matter, that acts throughout all the immensity of the solar system.

A first foundation was laid in biology. Malphigi making use of the microscope discovered the capillaries between the ends of the arteries and the veins, the air-cells in the lungs, the color cells beneath the outer layer of the skin, and along with Grew in 1670 began modern botany by pointing out the cell-system in plants and that flowers differ in sex analogously with animals. In 1677 Leeuwenhoeck discovered the animalculae in water, thus opening up a vast world of microscopic life hitherto undreamed of, in 1690 the actual capillary circulation, and made many important investigations on insect-anatomy.

In chemistry, which began to break away from alchemy, Boyle discovered that gases are compressed practically in proportion to the pressure upon them (about 1665). Mayow in 1674 demonstrated that there is some component in the air necessary for breathing and combustion, but his discovery had to be remade a hundred years later.

Thus the seventeenth century saw the work of the world's greatest astronomers, the foundation of physiology, the great law of gravitation, the first interpretation of sensation-light and sound-in terms of motion, the first law in chemistry, and the first insight into the world revealed by the microscope.

ANTHONY VON LEEUWENHOECK

ANTHONY VON LEEUWENHOECK was born at Delft, Holland, 1632. His trade was that of lens-maker for microscopes, and his scientific spirit led him from this into researches with the instruments he made.

He made several great discoveries and many others of less importance. In 1673 he noticed the red globules in the blood. In 1675 he discovered the animalculæ in water, thus making a first beginning in bacteriology. He first described the spermatazoa in 1677. In 1690 he traced the passage of the blood from the arteries into the veins by the capillaries, thus filling in the gap in Harvey's theory. He also noted the tubules of teeth, the solidity of hair, the structure of the epidermis. His descriptions of the anatomy of insects are classical. In theoretical biology he stood for the idea that everything generated its kind, and against spontaneous generation. Outside of his scientific studies his life was uneventful. Most of his discoveries were announced to the Royal Society of London. He died in 1723.

OBSERVATIONS ON ANIMALCULA SEEN IN RAIN, WELL, SEA AND SNOW-WATER; AS ALSO IN PEPPER-WATER

In the year 1675, I discovered very small living creatures in rain water, which had stood but few days in a new earthen pot glazed blue within. This invited me to view this water with great attention, especially those little animals appearing to me ten thousand times less than those represented by M. Swammerdam, and by him called water-fleas, or water-lice, which may be perceived in the water with the naked eye.

The first sort I several times observed to consist of 5, 6, 7, or 8 clear globules without being able to discern any film that held them together, or contained them. When these animalcula or living atoms moved, they put forth two little horns, continually moving. The space between these two horns was flat, though the rest of the body was roundish, sharpening a little towards the end, where they had a tail,

near four times the length of the whole body, of the thickness, by my microscope, of a spider's web; at the end of which appeared a globule of the size of one of those which made up the body. These little creatures, if they chanced to light on the least filament or string, or other particle, were entangled therein, extending their body in a long round, and endeavoring to disentangle their tail. Their motion of extension and contraction continued a while; and I have seen several thousands of these poor little creatures, within the space of a grain of gross sand, lie fast clustered together in a few filaments.

I also discovered a second sort, of an oval figure; and I imagined their head to stand on a sharp end. These were a little longer than the former. The inferior part of their body is flat, furnished with several extremely thin feet, which moved very nimbly. The upper part of the body was round, and had within 8, 10, or 12 globules, where they were very clear. These little animals sometimes changed their figure into a perfect round, especially when they came to lie on a dry place. Their body was also very flexible; for as soon as they struck against any the smallest fibre or string, their body was bent in, which bending presently jerked out again. When I put any of them on a dry place, I observed that, changing themselves into a round, their body was raised pyramidalwise, with an extant point in the middle; and having laid thus a little while, with a motion of their feet, they burst asunder, and the globules were presently diffused and dissipated, so that I could not discern the least thing of any film, in which the globules had doubtless been enclosed; and at this time of their bursting asunder, I was able to discover more globules than when they were alive.

I observed a third sort of little animals, that were twice as long as broad, and to my eye eight times smaller than the first. Yet I thought. I discerned little feet, whereby they moved very briskly, both in round and straight line.

There was a fourth sort, which were so small that I was not able to give them any figure at all. These were a thousand times smaller than the eye of a large louse. These exceeded all the former in celerity. I have often observed them to stand still as it were on a point, and then turn themselves about with that swiftness, as we see a top turn round, the circumference they made being no larger than that of a grain of small sand, and then extending themselves straight forward, and by and by lying in a bending posture. I discovered also several other sorts of

animals; these were generally made up of such soft parts, as the former, that they burst asunder as soon as they came to want water.

May 26, it rained hard; the rain growing less, I caused some of that rain-water running down from the house top, to be gathered in a clean glass, after it had been washed two or three times with water. And in this I observed some few very small living creatures, and seeing them, I thought they might have been produced in the leaded gutters in some water that had remained there before.

I perceived in pure water, after some days, more of those animals, as also some that were somewhat larger. And I imagine, that many thousands of these little creatures do not equal an ordinary grain of sand in bulk; and comparing them with a cheese-mite, which may be seen to move with the naked eye, I make the proportion of one of these small water-creatures to a cheese-mite to be like that of a bee to a horse; for, the circumference of one of these little animals in water is not so large as the thickness of a hair in a cheese-mite.

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 towards the oval point; and before the