io6 THE POPULAR SCIENCE MONTHLY 



came very late, perhaps not much more than one hundred years ago. The 

 first physical phenomena to be studied were, undoubtedly, those of day and 

 night, the rising and setting of the sun and moon, and the changes of the 

 seasons. We know very well that a people as highly cultivated as 

 the Greeks, although they were deeply interested in natural phenomena, 

 had an extremely small knowledge of the laws of nature and had not 

 learned how to investigate them. Although they possessed an excellent 

 knowledge of geometry, they had not the slightest idea of the nature or 

 laws of motion, whether celestial or terrestrial, and with the exception 

 of the properties of the lever and of liquids at rest, known to Archimedes, 

 their knowledge of physics was almost a blank, and yet their great phi- 

 losopher, Aristotle, dominated science until the sixteenth century of our 

 era. It was at this time that the dawn of modern physics took place 

 with the beginning of the experimental study of nature by Galileo. We 

 must remember that Aristotle suffered not so much from lack of knowl- 

 edge as from lack of appliances. What might he not have discovered 

 had he possessed a thermometer, a telescope or even a clock ! Neverthe- 

 less, Galileo did not possess these simple instruments, but he went to 

 work to make them possible. He invented the telescope and thus made 

 possible the searching of the mysteries of the heavens. Although he 

 had no clock, he studied the motions of the pendulum, formed by the 

 great lamp in the baptistery at Pisa, by comparing the time of its swing 

 with the number of beats of his pulse, thus making possible the applica- 

 tion of the pendulum to clocks by Huygens. As a contrast of Galileo's 

 method with that of the Greeks may be cited his experiment of dropping 

 a light and a heavy body from the top of the leaning tower of Pisa and 

 showing that both fell to the ground at the same time, instead of be- 

 lieving, as the Greeks had done from reasoning without experiment, that 

 the heavy body falls the faster. By careful study of the motions of a 

 ball rolling down an inclined plane, Galileo was able to enunciate the 

 precise law of falling bodies ; that their acceleration is uniform, that is, 

 that in equal times their velocity increases by equal amounts. The way 

 was thus prepared for Newton, who in the next century established the 

 connection of all forces with the accelerations produced by them and 

 was able to enunciate the laws of motion, both terrestrial and celestial, 

 in a form that has not been improved upon to-day, constituting one of 

 the most magnificent triumphs of the human intellect. Passing on 

 rapidly we find at the beginning of the nineteenth century the phe- 

 nomena of electricity beginning to attract the attention of investiga- 

 tors, while those relating to light had already made substantial progress. 

 All this time there had been nothing that could properly be called a 

 physical laboratory. Discoveries had been made by individual inquirers 

 working generally in such rooms as they had in their own houses with 

 the most meager facilities. We all remember how Newton bored a hole 



