upon the Collijion of Bodies. 351 
fame manner as before defended, and the body C to reft. The 
body D being let go, and linking the body C at reft, in con- 
fequence of the ftroke, the fprings being hooked up by the 
ratchets, they both move from their refting marks /, v, refpec- 
tively toward M : Now if they both moved together, and the 
rod ef covered the mark c, and the rod gh covered the mark d 
at their utmoft limit, then they would truly obey the laws of 
non-elaftic loft bodies; becaufe their medium afcent would be 
to the mark %, which is juft half the angle of afcent to the 
mark x ; but as in this piece of machinery, though the main 
or principle fprings are hooked up, yet every part ot them, and 
all the materials of which they are compoled, and to which 
they are attached, have a degree, or more properly {peaking, a 
certain compafs of elafticity , which, as fuch, is perfect, and no 
motion loft thereby. 
We muft not, therefore, expedt the two compound bodies 
after the ftroke to ftick together without ieparating, as would 
be the cafe with bodies truly non-elaftic and loft ; but that 
from the elafticity they are poflefled of, they will by rebound- 
ing be fepa rated ; but that elafticity being perfect, can occafion 
no lofs of motion to the fum of the two bodies ; l'o that if the 
body C afcends as much above its mark c as the body D falls 
ihort of its mark d, then it will follow, that their medium 
afcent will ftill be to the mark z, as it ought to have been, 
had theybeen truly non-elaftic foft bodies ; and this, in reality, is 
truly the cafe in the experiment, as nearly as it can be diicerned. 
After a few vibrations, by the rubbing of the fprings againft 
one another, they are loon brought to reft ; and heie they 
would always reft had they been truly and properly perfect 
non-elaftic foft bodies; but here, as in the cafe of thefe 
bodies, by a change of the figure and fituation of the compo- 
nent parts, there is expended one half of the mecnamcai pow et 
