Page:Popular Science Monthly Volume 78.djvu/340

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swinging to and fro, and yet it had awaited the coming of Galileo to read its inner meaning!

On the question of falling bodies Galileo ran counter to Aristotle. That philosopher had taught that bodies in falling acquire velocity in proportion to their weight. Galileo found by a simple but careful study that all bodies acquire the same velocity in falling. With the imprudence of youth he forthwith proclaimed the errors of Aristotle from the house-tops, much to the scandal of his classical friends. In answer to their protests he proposed an experiment, and this experiment was made. The faculty of the University of Pisa together with the interested or curious of the city gathered at the leaning tower—"Pisa's leaning miracle," as Whittier calls it. From the top and at the overhanging side Galileo let fall a one-pound and a one-hundred-pound shot. The two shot started, fell—and struck the ground together. As Lodge exclaims, "The simultaneous clang of those two weights sounded the death-knell of the old system of philosophy and heralded the birth of the new." And yet, it is recorded that while some saw, and were convinced, others—nor is their race extinct to-day—saw, but, consulting their copies of Aristotle, disbelieved.

Following in Galileo's foot-steps—perhaps more cautiously lest he be made to suffer for it—Huygens (1629-1699) further developed and extended the science of mechanics. In particular may be noted his development of the theory of circular motion; the invention, or at least perfection, of the pendulum clock, and this determination of the acceleration of gravity from pendulum observations, a method which is to-day the most accurate one in use. Huygens shares with Galileo all the honors due a scholar and original worker of the first rank. They resemble each other in character, in method and in the great value of their labors.

As bearing upon the law of gravitation the theory of circular motion was of the very greatest value. Without it, Newton must either have failed in his task or have discovered these principles for himself. As a matter of fact he did the latter. Huygens was also the first to grasp the significance of the following occurrence. In 1671 Jean Richter, in the course of astronomical work, carried a pendulum clock from Paris to Cayenne in South America. The clock kept correct time in Paris, but at the latter station it daily fell two and a half minutes behind mean solar time. The pendulum was shortened to correct it, but on returning to Paris it was found to gain time at the same rate that it had before lost it. Huygens at once correctly explained this as due to the rotation of the earth on its axis; thus furnishing the first experimental evidence of the earth's rotation.

The span of Galileo's life was from 1664 to 1642. He died discredited by his church, deprived of his liberty and afflicted with blind-