upon the CoWjion of Bodies . 
ing the proper material for an experiment, in anfwer to a con- 
clufion drawn from an abftra& idea. On the other hand, if it 
can be ftiewn, that the figure of a body can be changed, with- 
out a power, then, by the lame law, we might be able to make 
a forge hammer work upon a mals of foft iron, without any 
other power than that neceflary to overcome the friction, re- 
finance, ano original vis inertic?^ of the parts of the machine 
to be put in motion : for, as no progrefiive motion is given the 
mafs of iron by the hammer (it being lupported by the anvil)*,, 
no power can be expended that way ; and if none is loft to* 
the hammer from changing the figure of the iron, which is 
the only eftedt produced, then the whole power muft refide in 
tne hammer, and it would jump back again to the place from 
which it fell, juft in the fame manner as if it fell upon a body 
perfectly elaftic, upon which, if it did fill, the cafe would really 
happen : the power, therefore, to work the hammer would 
be the lame, whether it fell upon an elaftic or non-elaftic body ; 
an idea fo very contrary to all experience, and even apprehen- 
fton, of both the- philofopher and vulgar artift, that I fhcdl 
here leave it to its own condemnation. 
As nothing, however, is fo convincing to* the mind as expe- 
riments obvious to the lenfes, I was very defirous of contriving 
«:n experiment m point ; and as I law no hopes of finding mat- 
ter to make a direct experiment, I turned my mind towards an 
indirect one ; fo circumfcribed, however, as to prove incon- 
teftably, that the refult of the ftroke of two non-elaftic per- 
fectly hard bodies could not be the fame as would refult from 
the collilion of two foft ones ; that is-, if it can be bona fide 
proved, that one half of the original power is loft in the ftroke 
of foft bodies by the change of figure (as was very ftronglv 
fuggefted by the mill experiments); then fince no fuch loft 
