MOVING FORCE. 
239 
changes of figure, are, indeed, the chief occupations of prac- Cases 
tical men in the construction and management of machinerj’. doctrines of 
The force spent in producing change of figure in the colli- 
sion of bodies, was noticed by John Bernoulli in his dissertation 
De vera notione virium vivarum, as follows. Si corpora 
non sunt perfecte elasticn, aliqua pars virium vivarum, quae pe- 
riisse videtur, consumitur in compressione corporum, quando 
perfecte se non restituunt j a quo auteni nunc abstrahimns, 
concipientes, compressionem illam esse similem compressioni 
e'astri, quod post tensionem factatn impediretur ab .aliquo reti- 
naculo, quo minus se rursus dilatare posset, et sic non redderet, 
sed in se retineret vim vivam, quam a corpore incurrenfe ac- 
cepisset : unde nihil virium periret, etsi periisse videretur*.” 
From this passage, and from various other passages in his 
works, relating to the doctrine “ de conservatione virium viva- 
rum,” it appears, that Bernoulli thought it necessary to maintain 
that no force could be lost, and that even in the collision of non- 
elastic bodies he considered the change of figure to be such, 
that the force which had been expended in producing it might 
be recovered by the restoration of the figure, or by some other 
means. Why he considered it incumbent upon him to main- 
tain such opinions, or upon what foundation he understood 
them to rest, it is hard to say. Experience famishes us with 
nothing which can justify the conclusion, that the force spent 
in producing change of figure in nonelastic bodies, can ever b« 
restored. 
I believe Mr. Smeaton was tlie first who subjected to actual 
admeasurement the force spent in producing change of figure 
in the collision of nonelastic bodiesf. He appears to have been 
led to this investigation, not by curiosity merely, but by a con- 
viction of the insufficiency of the prevailing doctrines of 
forces to account for the facts which were constantly presented 
to him in his ordinary occupations, and particularly, as 1 have 
before observed, in the action of water on water wheels. It is 
BernoDlli’s works, vol. iii, p SSo. 
f Phil. Trans. l78?. 
