[ ’9 ] 
will be a conftant Endeavour in thofe Particles to 
recede further from each other; fo that the more 
they are confined, or compreiTed, the greater will 
be their elaftic Power : Whereas in folid Bodies, this 
Property of Elafticity proceeds chiefly from Attrac- 
tion, or a Nifus in the component Particles to fly 
back, or run into clofe Conta&s again, whenever 
they happen to be ftretched out, or bent, fo as to 
touch each other in fewer Points. 
XLL 
From what has been faid we may deduce the 
following Corollary , viz- That whenever Elafticity 
proceeds from the Principle of Repul[ion y as it does 
in Air, Vapours, &c. fome CompreJJion is neceflary, 
in order to force the elaftic Matter into a narrower 
Compafs than it would otherwife poflefs; but when 
it arifes from Attraction, as in the mufcular Fibres, 
and all folid Bodies, fome diftr affile Force, is requi- 
re to disjoin the component Particles from their 
ufual Conta&s, before it can exert its Power; and 
perhaps, for want of attending to this Difference, 
fo many various Opinions may have arifen concern- 
ing the Caufe of Elafticity. 
XLII. 
In my next Lecture I fhall confider the Shape 
of the mufcular Fibres, and the Caufe of mufcular 
Adlion. 
