274 Dr. Reynolds on Meteors. 
ihe fire, the greater in a due ratio is the absolute quantity of 
heat required to reduce it to, and retain it in, the state of gas, 
the greater, in a corresponding degree, will be the dilata- 
tion of its particles and decrease of its specific gravity. Hence, 
if water reduced to vapor by heat, be capable of assuming an 
altitude of two miles, it follows that more refractory substances 
reduced to a similar state, will suffer expansion and fugacity in 
a due proportion to the quantity of caloric they employ, and 
will assume a corresponding elevation, as already inferred under 
my first head. 
Another objection may be that though high degrees of heat 
affect certaii solids as above stated, yet these cannot be sensi- 
bly acted on by such feeble agents as atmospheric air and the 
rays of the sun. I answer, if it be admitted that sensible heat 
acts on solids in an increasing ratio to its intensity, it follows 
that lower degrees, though acting in an inverse ratio to higher. 
must affect the same bodies in a conceivable degree at any tem- 
perature above their natural zero :* and though the heat of 
the sun beating on a plane surface for several hours is feeble; 
compared with that produced by a burning lens, or air furnace, 
yet if it be sufficient to detatch from one square foot of the 
earth’s surface the 104023 part of a grain in twenty-four hours; 
the quantity taken from 100 square miles, in the same time 
and proportion, would amount to ten pounds, which is abund- 
antly sufficient for all meteoric phenomena; and the loss to 
each square foot, supposing the process to be uninterrupted, 
would be no more than one grain in 284 years. When we ad- 
vert to the intense heat produced by concentrating 4 few of 
agk rays in a burning lens, the whole quantity daily sent 
el earth must strike us forcibly. If collected in @ lens © 
"It may be easily proved that water evaporates (though slowly) at tei 
perature many degrees below its freezing point; and these vapors are _ 
subtle and elastic than those formed at the boiling point of that fluid. 
emark.—tt is indeed proved that vapor is formed from water at the lowest 
temperatures, but is less elastie, the lower the temperature, as appears hes ® 
sustaining a continually decreasing column of mercury, the lower wae 
perature at which the vapor is formed. Vide Dalton’s and Gay Lussac’s © 
penments.— editor. 
