280 THE CHEMISTEY OF CREATION. 



elasticity from a volatile substance, mingle itself 

 with the surrounding air, and extend its in- 

 fluence until its effects become so enfeebled 

 by dilution, as to be imperceptible to the 

 sense." 



The presence of moisture also favours the 

 escape of disagreeable odours; and it may be 

 noticed, that in damp weather, the exhalations 

 from reservoirs of putrid matter are more abun- 

 dant than at other times. It appears, also, that 

 alkalies favour the escape of vapours and organic 

 exhalations into the air. 



We must, however, now proceed to inquire 

 how it happens that dew, or water in its 

 other form, becomes thus dissipated and lost 

 in air? By the way-side, a week ago, was a 

 pool, some six or twelve inches deep, a place 

 for ducks to sport in, and for thirsty cattle 

 to drink. Where is it now? The parched, 

 cracked mud at its bottom is all laid bare. It 

 is certain that it has not sunk into the earth, for 

 the subsoil is a heavy clay; it has all become 

 dissipated into the air, in the form of vapour : 

 in other words, it has evaporated. A saucer 

 full of water placed on a sunny window-sill, 

 becomes emptied by this invisible force before 

 night 



It is found that water and all liquids evapo- 

 rate, or pass off invisibly into the air, even at low 



