2 Wilde, Moving Force of Terrestrial mid Celestial Bodies. 



3. Although Galilei had long before demonstrated 

 that the spaces described by heav}- bodies from the 

 beginning of their descent are as the squares of the 

 times and also of the velocities acquired in falling through 

 those spaces, yet the significance of this law in relation to 

 the moving force of bodies was entirely overlooked until 

 Leibnitz made the announcement that the force of a body 

 in motion, by the free action of gravity, is as the square 

 of the velocity. To this measure of moving force 

 Leibnitz applied the term, vis viva, or living force. 



4. The controversy which has since gathered round 

 the question of the measure of moving force and still 

 remains unsettled, forms a remarkable chapter in the 

 history of the physical .sciences. As might have been 

 anticipated, a priori philosophers, mathematicians, meta- 

 physicians, and men of letters, unskilled in experimental 

 methods of interrogating nature, adopted the Cartesian 

 measure of moving force. Of these ma}' be mentioned, 

 Maclaurin, Hutton, and Young ; Locke, Kant, Schopen- 

 hauer, Voltaire, and other writers of more or less note up 

 to the present epoch. Happily for the progress of science 

 a number of natural philosophers, among whom Smeaton, 

 Wollaston, Ewart, Dalton, Joule, and Fairbairn stand 

 pre-eminent, have proved conclusively by various methods, 

 that the true measure of the moving force of a body 

 under the free action of gravit)- is as the square of the 

 velocity.* Nevertheless, modern scholasticism has not yet 

 pronounced decidedly in favour of the law, and the 



* These results have been abundantly confirmed by my e.Kperiments with 

 the gyroscope described in the lecture referred to, wherein it was shown 

 (l) that four limes the weight falling from the same height were required to 

 generate a double velociiy of the revolving disc ; (2) that one unit of weight 

 falling through four times the height also generates a double velocity of the 

 disc ; (3) that the moving force required to generate a double velocity of the 

 disc is independent of the time of its application and is as the scjuaie of ihe 

 velocity. — Manchester Metnotrs, vol. 46, no. 10, 1902. 



