[ 2 4 2 ] 
The probability, fupporting the hypothecs of Mr. 
Eeles, according to his own expreffions, refts on this : 
“ That every particle of vapour is endued with a 
“ portion of eledtric fire ; and that there is no other 
t£ fufficient caufe affigned for their afcending.” (Phil. 
1 Tranj, ' voL xlix. part. i. p. 134.)* My defign is there- 
fore firft to attempt to fhew, that another theory, 
founded on principles better known, will lufficiently 
explain the afcent of vapours : and then, that fome 
kinds of vapours are not endued with a more or lefs 
than their natural fhare of eledtric sether. 
The immenfe rarefadtion of explofive bodies by 
heat, depends either on the efcape of air before con- 
denfed in them, or on the expanlion of the conftituent 
parts of thofe bodies. This diflindtion has not been 
lufficiently confidered by any one to my knowlege ; 
nor fhall I at prefent amufe the Society upon this 
head ; it being enough for my prefent purpofe to ob- 
ferve, that they may be thus diftinguifhed : where air 
is emitted, it cannot be condenfed again into the fame 
bulk by cold; but the expanfion of heated parts of 
bodies, as foon as that heat is withdrawn, ceafes to 
exift. 
Nitre comes under the firft of thefe claffes : in de- 
tonation it emits great quantities of air, not after- 
wards condenfible to the like fpace. This may be 
feen by firing a few grains of gunpowder in an 
unblown bladder, or in a veffel nearly full of water 
with its mouth inverted. The fame is true of all the 
folid parts of animals and vegetables, when fubjedt- 
cd to fire ; as appears from the experiments of that 
learned philanthropic, Dr. Hales. 
But of water the contrary is evident. In the ftcam- 
engine, 
