AGRICULTURAL METEOROLOGY. 143 
7. Compound arable soils are generally lighter as they are propor- 
tionally richer in humus. This fact alone does not positively indicate 
the fertility of asoil, since the humus itself differs in weight, and the 
other pure earths exhibit diversity of weight according to their ‘fineness ; 
consequently, mixed earths may acquire very different average weights. 
On this point specific gravity furnishes more certain evidence than abso 
lute weight. 
8. The designations of light and heavy soils, as usually employed, 
‘refer to the different consistence of the earths, and not to their specific 
gravity or absolute weight; clay soils, wet and dry, are heavier than 
sandy soils. 
Weight of artificial mixtures of earths.»When different earths are ar- 
tificially combined, a cubic inch of the compound gives a greater weight 
than the common average of the component earths, whether mixed in 
equal portions, according to weight and volume, or in other quantities. 
Power of soil to contain water .—By this term we understand the prop- 
erty of earths to receive and retain water within their interstices, 
without allowing any to escape. Itis of the greatest importance to 
vegetation, for on it depends the quantity of aqueous nourishment the 
soil can receive and supply to the roots of plants—an essential source 
of vegetable nutriment. 
1, The sands are most deficient in this power; its degree varies, ac- 
cording to fineness in the grain, from 20 to 40 per cent.; siliceous sand 
has the least power of all. 
2. Gypsum powder approaches the sands in this respect, and has even 
less power of containing water than calcareous sand. 
3. Slaty marl, despite its proportion of clay, exhibits very little of 
this power, and renders soil both warm and dry. This marl is fre- 
quently applied to the improvement of vineyards in Germany. 
4, In carbonate of lime this water-holding power varies according to 
fineness of the particles; a distinction is important, therefore, between 
the fine lime separated by decantation and the earthy lime as found in 
the form of sand in arable lands. 
5. Carbonate of magnesia exists in a coarse-grained state, combined 
with lime or siliceous earth, in arable soils, and retains water only in a 
slight degree, 
6. Humus, with its large natural proportion of half-decomposed or- 
ganic remains, as wood, leaves, roots, &c., has the greatest degree of 
this power. One hundred parts of the fine earth formed by decaying 
wood in old trees are capable of absorbing nearly two hundred parts of 
water; and some light turfearths can contain from three hundred to 
three hundred and sixty parts, even when dried artificially. Where we 
meet with the power of retaining more than ninety parts of water, we 
may depend upon an abundant commixture of organic matter. 
Firmness and consistency of soil—These two qualities are of agreat im- 
portance in regard to the fertility and the manipulation of land; the 
terms, universal in husbandry, of light and heavy soil, rest mainly on 
these properties, and they therefore deserve investigation in regard to 
both dry and moist conditions of the earth. 
1. If we compare the consistency of earths with their weight, we shall 
see that the customary terms of heavy and light soil are founded upon 
the cohesion of soil within itself and its adhesion to agricultural imple- 
ments, and they therefore indicate its working properties rather than 
its weight. The comparative ease with which roots penetrate the soil 
will probably accord with these conditions. 
2. The consistency and firmness of soils in the dry and wet state in- 
