Analyfis of the Air. 313 
that the rays of light be bodies of different 
“ fizes ; the leaft of which may make the 
<c weakeft and darkeft of the colours, and 
“ be more eafily diverted, by refrading fur- 
<c faces from the right courfe; and the reft, 
iC as they are bigger and bigger, may make 
“ the ftronger and more lucid colours— 
^ and be more and more difficultly diverted,, 
§ lu . 29. So 30, he obferves of air, that 
“ denfe bodies by fermentation ratify into 
“ feveral forts of air, and this air, by fer~ 
ct mentation, and fometimes without, returns 
into denfe bodies/* And fince we find 
in fad from thefe Experiments, that air a- 
rifes from a great variet of denfe bodies, 
both by fire and fermentation, it is probable 
that they may have very different degrees of 
elafticity, in proportion to the different fize 
and denfity of its particles, and the different 
force with which they were thrown off in- 
to an elaftick ftate. “ Thole particles (as 
Sir Isaac Newton obferves) receding 
cC from one another, with the greateft re- 
“ pulfive force, and being moft difficultly 
“ brought together, which upon contad 
f* cohere moft ftrongly/* Whence thofe of 
the weakeft elafticity, will be leaft able to 
frefift a counter-acting power, and will there- 
fore 
