[ 9 1 
XIX. 
Sir Ifaac Newton * thinks, that not only Water 
and Air are convertible into denfe Bodies, but that 
even Light may become a Part of grofs Bodies, and 
that they may receive much of their Activity from 
the Particles of Light which enter their Compofition. 
It is the Opinion alfo of Monf. Homberg, that Light 
or Fire is a Part of the Compofition of all Things ; 
though in the Analyfis of Bodies it is always loft, 
efcaping the Skill of the Artift, and palling through 
the clofeft Yeflels. 
XX. 
We all know that folar Fire, or Light, adds 
Weight to Lead, Tin, or Regulus of Antimony, 
when expofed to the Fire of a burning Glafs, though 
they otherwife lofe much in Smoak and Steam. But 
to proceed ; 
XXL 
Thefe then being then the component Parts of 
the mufcular Fibres, our next Task is to fhew the 
Caufe of their Tenfion and Elafticity. 
XXII. 
That all the mufcular Fibres of the Body are in 
a State of T enfioh, during Health, is manifeft from 
every 
* Opt, £)u. 30. 
. B 
