126 
On the Lifluence of Water 
practical men should experiment, to ascertain the facts in question. 
Nevertheless, the labours of the laboratory are not to be rejected ; 
it is by their agency, chiefly, that we have acquired our complete 
knowledge of the phenomena of water ; and investigations con- 
ducted in the closet may materially aid the experimentalist in the 
field. I have extracted the following opinions and researches 
from the works of two distinguished British philosophers, as they 
relate to the affinity to moisture and heat of many bodies found 
in soil, and illustrate this division of the subject. 
Professor Leslie, who added largely to our knowledge of the 
phenomena of heat and moisture, thus introduces the mention of 
his experiments on the hygrometric powers of some of the earths, 
which, for the sake of brevity and perspicuity, are collected in 
the following table : — 
" Absorbent substances, besides assimilating to their essence a portion 
of the liquid which touches them, are likewise disposed to attract, 
though with various energy, the humidity of the atmosphere. The more 
solid, as well as the softer, materials exert this power, and which is 
exactly analogous to that of the concentrated acids and the deliquescent 
salts. In their several affinities to moisture the earthy bodies discover 
the most essential ditferences of constitution. To examine these pro- 
perties, let the substance be dried thoroughly, and almost roasted before 
a strong fire, and introduced immediately into a phial with a close 
stopper; the powder having undergone that sort of preparation is, at 
any time afterwards, thrown partially into a very large wide-shaped 
bottle, and shut up till it has attracted its share of humidity from the 
confined air; and a delicate hygrometer being now let into the bottle, 
indicates the measure of the eftect produced by absorption." 
Degrees of Moisture 
Absorbed from Air 
at about 60°. 
Clay, very highly torrefied . . . . . 8 
Silica, ditto . . . • . .19 
Whinstone ditto 23 
Carbonate of strontites . . . • . . 23 
Carbonate of barytes . . • . . .32 
Clay, strongly roasted ...... 35 
Silica, soaked in water, and dried after high torrefaction 35 
Silica, in its natural state . . . . . 40 
Carbonate of lime . . . . . .70 
Shelly sea-sand ....... 10 
Carbonate of magnesia ...... 75 
Sea-sand, from a sheep-walk . . . . .78 
Whinstone, in its natural state . . . ,80 
Alumina ........ 84 
Pipeclay ........ 85 
Sea-sand, cultivated . . . • . .85 
Whinstone, in a crumbling state . . . . 86 
Ditto, reduced to mould . . . .92 
Garden mould ....... 95 
