274 Dr, Reynolds on Meteors. , 



the 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, 

 gnd the greater, in a corresponding degree, will be the dilatation 

 of its particles and decrease of its specific gravity. Hence, if 

 water reduced to vapour by heat, be capable of assuming an 

 altitude of two miles, it follows that more refractory substances 

 reduced to a similar state, will suifer expansion and fugacity in 

 a due proportion to the quantity of caloric they employ, and 

 will assume a corresponding elevation, as already inferred un- 

 der my first head. 



Another objection may be, that though high degrees of heat 

 affect certain 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 increeising 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 detach 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 a few of 

 the sun's rays in a burning lens, the whole quantity daily sent 

 to the earth must strike us forcibly. If collected in a lens of 



* It may be easily proved that water evaporates (though slowly) at a tempera- 

 ture many degrees below its freezing point ; and these vapours are more subtle 

 and elastic than those formed at the boiling point of that fluid 



It is indeed proved that vapour is formed from water at the lowest temperatures, 

 but is less elastic, the lower the temperature, as appears from its sustaining a con- 

 tinually decreasing column of mercury, the lower the temperature at which the 

 Trapour is formed. Vide Dalton's and Gay Lnssac's experiments. Editor. 



