ON THE PHYSICAL VIEW OF NATURE. 



101 



Poncelet 



work " for the definite quantity which had before him 

 been variously designated as power, effect, action, &c., 

 and he distinctly states that the inertia of matter trans- introduces 



the term 



forms work into vis viva and vis viva into work. He 

 also measures this quantity " work " quite in the modern 

 fashion by the " kilogrammetre," which gives the same 

 conception as the foot-pound, only in a different measure. 

 Long before the terminology thus invented and fixed 

 by Watt, Young, and Poncelet had been accepted by 

 scientific writers, a change in the current notions on 

 the forces of nature had been gradually brought about 

 from quite a different quarter. Uninfluenced by the 

 theoretical views which were developed and firmly held 



mathematics was not merely the 

 science of magnitude, but quite as 

 much that of position, of design 

 and perspective, of mechanical 

 work and effect. They introduced 

 a whole series of new and practical 

 ideas, drawn from their own appli- 

 cations, and created a new vocab- 

 ulary. They worked hand in hand 

 with physicists and chemists, some 

 of whom had little taste for the 

 extremely abstract and analytical 

 methods of the school of Laplace 

 and Cauchy. Poncelet's original 

 geometrical work, which will oc- 

 cupy us in a later chapter, led him 

 into many controversies. It was, 

 however, greatly appreciated in 

 Germany and later in England. 

 His influence on German applied 

 mechanics has been quite as great 

 as that on geometry ; and the great 

 text-books of mechanics by Weiss- 

 bach, Redtenbacher, Riihlmann, and 

 others, are as much indebted to 

 Poncelet and other French models 

 as the German text-books on mathe- 

 matics, physics, and chemistry were 

 for a long time to the well-known 

 works of Biot, Pouillet, Cauchy, 



Francceur, Lame, Regnault, and 

 others. The influence of Ponce- 

 let on practical mechanics, and 

 especially in the fixing of an ade- 

 quate terminology, can therefore 

 be studied equally well in French 

 and in German historical writings. 

 Among the former I may mention 

 especially the ' Expose" de la Situa- 

 tion de la M&anique applique"e 

 par Combes, Phillips et Collignon,' 

 Paris, 1867, and among the latter, 

 notably the above-mentioned writ- 

 ings of Helm, who traces the 

 growth of the conception of me- 

 chanical work in French writings, 

 and its influence on German thought 

 ('Energetik,' p. 12, &c.) See also 

 Diihring, loc, cit., p. 471, &c. I may 

 also refer to Heun's Report (' Jahres- 

 bericht der deutscheu Mathemat- 

 iker- Vereinigung, ' vol. ix. part 2, 

 1901), where the sciences comprised 

 in "Mechanics" are distinguished 

 according as they are astronomical 

 (Laplace, Poincare'), physical (Eng- 

 lish mathematical physics, Kirch- 

 hoff, Helmholtz, Hertz), geometrical 

 (Poinsot, Charles, Ball), or techni- 

 cal (Watt, Poncelet, Rankine). 



