26 ILLINOIS ACADEMY OF SCIENCE 



It is true, indeed, that during this interval a large number 

 of isolated physical facts had been discovered; indeed there is 

 scarcely a chapter in physics in which some advance of this 

 type can not be mentioned ; but, during all this while, nothing 

 in the way of development is seen ; individual discoveries re- 

 main isolated ; they do not bear fruit ; speculation and guess- 

 ing were still employed where we use observ^ation and meas- 

 urement and computation. Leonardo da Vinci likens a scien- 

 tific conquest to a military victory in which theory is the 

 field marshal ; experimental facts, the soldiers. The philoso- 

 phers who preceded Galileo had. in the main, been trying to 

 fight battles without soldiers. The only possible exceptions 

 to tliis statement are Roger Bacon, Leonardo da Vinci, Ste- 

 vinus and Gilbert. They had measvired some mechanical 

 quantities — a few of them — masses and stresses — such as 

 could be obtained by means of a steel-yard and a measuring 

 stick ; but they were still in the domain of statics. Xow from 

 a geometrical, esthetic or even utilitarian standpoint, it is 

 difftcult to imagine any finer sul)ject than graphical statics; 

 and yet when we regard the progress of physics, statics ,is 

 to dynamics somewhat as osteology is to physiology, a veri- 

 table valley of dry bones. The live part of mechanics is 

 kinetics, the study of masses which are in motion, the con- 

 sideration of bodies which are changing their velocities, cur- 

 rents of water, oscillating magnets, vibrating strings, rotating 

 wheels, electric motors, heat engines, electromagnetic waves, 

 and X-rays. These are the problems over which men lose 

 sleep; these are the questions which com]:Jel the interest of 

 the physicist ; these are the subjects whose mastery confers 

 power upon the engineer. The one confessed aim of physical 

 science is, indeed, to describe the motion of bodies in the 

 simplest possible manner. Indeed it is only by the aid of 

 this modern science of the energy of motion that any of the 

 ancient mechanical doctrines — such as the atomic theory of 

 Democritus — have acquired validity; it is this same science 

 which has rendered the heliocentric theory of Copernicus not 

 merely "a plausible view" but the one possible view. 



We pass now to a more definite question, namely, what 

 contribution did "our Academician" make to the solution of 

 problems of this type, to the science which now goes by the 

 name of physics? To answer briefly and baldly, he instituted 

 the method and set into motion the machinerv by which prac- 

 tically all these problems have been solved, in so far as they 

 have been solved at all. But lest I give the false impression 

 that Galileo was the ancester of all the physical sciences. T 

 hasten to a more detailed answer to the query. What did 

 Galileo? 



