[ 175 ] 
Though the particles of fluids, in common evapo- 
ration, are raifed into the atmofphere, by the at- 
trading and diflblving power of the air, yet in fome 
particular cafes vapours will rife into the air on an- 
other account j for in fome places the earth often 
fends forth hot elaftic vapours that rife into the air 
by means of their elaftlcity, and carry with them 
mineral particles of different kinds. Fermentation 
generates elaflic vapours, which expand themfelves 
into the air. And the particles of water, when 
fufflciently heated, acquire a repelling force, which 
feparates them from the furface of the water, and 
" throws them upwards into the air. But all thefe 
vapours foon lofe that elafticity by which they were 
firlf raifed, and they are then retained, and kept 
fufpended in the air, by the fame power that keep 
fufpended all thefe vapours that rife without any 
elaflicity in common evaporation. That the parti- 
cles of fleam, which rifes from hot water, are en- 
dued with a repelling force, appears plainly when 
water is boiled in a clofe veffel j for then the fleam 
becomes fo exceedingly elaflic, that, unlefs proper 
caution be ufed, it will burff the ffrongefl veflel. 
In this cafe the boiling water, being ftrongly prefled 
by the force of the included fleam, conceives a much 
greater heat, than it will do in an open veflfel ; for 
even when water is boiled in the open air, it is fome- 
M^hat hotter when the atmofphere is heavy, than 
when it is light, which fhews that prefiure, upon 
boiling water, increafes its heat j the reafon of which 
we fliall fee prefently. 
But the mofl: remarkable phasnomenon that at- 
tends the boiling of water, is thofe large bubbles 
which 
