While hardly anything was done in chemistry, a large number of phenomena in the field of physics were observed now for the first time. Leonardo da Vinci measured the rapidity of falling bodies, by dropping them from towers and having the time of their passage at various stages noted. He thus found, correctly, that their velocity increased. It is also said that he observed that bodies always fell a little to the eastward of the plumb line, and thence concluded that the earth revolved on its axis. He made careful experiments with billiard balls, discovering that the {614} momentum of the impact always was preserved entire in the motion of the balls struck. He measured forces by the weight and speed of the bodies and arrived at an approximation of the ideas of mechanical "work" and energy of position. He thought of energy as a spiritual force transferred from one body to another by touch. This remarkable man further invented a hygrometer, explained sound as a wave-motion in the air, and said that the appearance known to us as "the old moon in the new moon's lap" was due to the reflection of earth-light.
Nicholas Tartaglia first showed that the course of a projectile was a parabola, and that the maximum range of a gun would be at an angle of 45 degrees.
Some good work was done in optics. John Baptist della Porta described, though he did not invent, the camera obscura. Burning glasses were explained. Leonard Digges even anticipated the telescope by the use of double lenses.
Further progress in mechanics was made by Cardan who explained the lever and pulley, and by Simon Stevin who first demonstrated the resolution of forces. He also noticed the difference between stable and unstable equilibrium, and showed that the downward pressure of a liquid is independent of the shape of the vessel it is in and is dependent only on the height. He and other scholars asserted the causation of the tides by the moon.
[Sidenote: Magnetism]
Magnetism was much studied. When compasses were first invented it was thought that they always pointed to the North Star under the influence of some stellar compulsion. But even in the fifteenth century it was noticed independently by Columbus and by German experimenters that the needle did not point true north. As the amount of its declination varies at {615} different places on the earth and at different times, this was one of the most puzzling facts to explain. One man believed that the change depended on climate, another that it was an individual property of each needle. About 1581 Robert Norman discovered the inclination, or dip of the compass. These and other observations were summed up by William Gilbert [Sidenote: Gilbert] in his work on The Magnet, Magnetic Bodies and the Earth as a great Magnet. [Sidenote: 1600] A great deal of his space was taken in that valuable destructive criticism that refutes prevalent errors. His greatest discovery was that the earth itself is a large magnet. He thought of magnetism as "a soul, or like a soul, which is in many things superior to the human soul as long as this is bound by our bodily organs." It was therefore an appetite that compelled the magnet to point north and south. Similar explanations of physical and chemical properties are found in the earliest and in some of the most recent philosophers.
[Sidenote: Geography]
As might be expected, the science of geography, nourished by the discoveries of new lands, grew mightily. Even the size of the earth could only be guessed at until it had been encircled. Columbus believed that its circumference at the equator was 8000 miles. The stories of its size that circulated after Magellan were exaggerated by the people. Thus Sir David Lyndsay in his poem The Dreme [Sidenote: 1528] quotes "the author of the sphere" as saying that the earth was 101,750 miles in circumference, each mile being 5000 feet. The author referred to was the thirteenth century Johannes de Sacro Bosco (John Holywood). Two editions of his work, De Sphaera, that I have seen, one of Venice, 1499, and one of Paris, 1527, give the circumference of the earth as 20,428 miles, but an edition published at Wittenberg in 1550 gives it as 5,400, probably an {616} attempt to reduce the author's English miles to German ones. [Sidenote: 1551] Robert Recorde calculated the earth's circumference at 21,300 miles.[2]
Rough maps of the new lands were drawn by the companions of the discoverers. Martin Waldseemuller [Sidenote: 1507] published a large map of the world in twelve sheets and a small globe about 4 1/2 inches in diameter, in which the new world is for the first time called America. The next great advance was made by the Flemish cartographer Gerard Mercator [Sidenote: Mercator, 1512-94] whose globes and maps—some of them on the projection since called by his name—are extraordinarily accurate for Europe and the coast of Africa, and fairly correct for Asia, though he represented that continent as too narrow. He included, however, in their approximately correct positions, India, the Malay peninsula, Sumatra, Java and Japan. America is very poorly drawn, for though the east coast of North America is fairly correct, the continent is too broad and the rest of the coasts vague. He made two startling anticipations of later discoveries, the first that he separated Asia and America by only a narrow strait at the north, and the second that he assumed the existence of a continent around the south pole. This, however, he made far too large, thinking that the Tierra del Fuego was part of it and drawing it so as to come near the south coast of Africa and of Java. His maps of Europe were based on recent and excellent surveys.
[Sidenote: Astronomy]