88 On Fertility.|[Aug.

vious fertility, than on that which poſſeſſes much,—The farther removed the mould is from the point of the ſaturation of fertility, the more greedily is fertility imbibed by it. Be it remem- bered, that between Air and Mould is no tranſmiſſion of fertility where there is no conta&t,—’T hat the middle of a dung heap retains its fœtid aivity on opening; and much more ſafely 1s

‘fertility retained by mould, which is never half. ſaturated.,

The beneficial‘operation of fallowing may therefore be thus deſcribed: The external ſurface(having received an acceflion of fertility from the air) is mingled with the other mold as deep- as the plough goes—a ſurface(moſtly) new reſults, which in its turn is fertilized; and thus ſucceſſively the mould is enriched ac- cording to the repetitions of plouging, or other mode of admix- ture.—But according to the fore-going theory, leſs and leſs fertility is induced at each freſh expolure, as the improving mould accedes nearer and nearer to the limit of fertility, and if(inſtead of expoſing a ſurface already partially fertilized) it were poſſible to cover the old ſurface with ſucceſſive thin coats of ferile mould the firſt acquired fertility would remain under ground in ſtore, (xzumaiov), while the acquiſition of new" fertility would go on wich the utmoſt poſſible rapidity from the unſated yoracity of à more hungry ſurface—and the oftener ſuch ſurface was renewed, the faſter would be the acceſfion of fértility—“ But ſuch ſuper- indudion of férile ſurface is impoſſible:” it is ſo; but it is not impoſſible to purſue the principle to an efficient extent in prac- tical agriculture by a very obvious and eaſy expedient. This conſiſts merely in plouging to a greater depth than is uſual, Suppoſe(for inſtance) lix inches, the uſual depth, augmented to nine inches, the new mould laid n the ſurface by the plough would rapidly imbibe the influences of the air; and if Lhe leſs laborious ſorts of culture, harrowing, and rolling, were Aulouf ly employed to increaſe the imbibing ſurface of this new mould by pulverization,$ it ſeems not doubtful that in the courſe of a ſummer, this new mould would imbibe much more fertility from the air, than would any expoſure of mould already tolerably fertile. This for the firſt year: afterwards no ſeparation of the old and new mould could be effeted; but the increment of ferti- lity would fill be greater than under the circumſtance of ſhal- low cultivation. For, if after an exhauſting crop, two fields ploughed to the diferent depths of ſix and nine inches be left equally impoveriſhed, the total remaining fertility of the nine

{ The effeâ of a change of air on the human frame is proof enongh of the powerful-mutual aftion ot air and mould; for as the air is ſo conſcantly mov-

ing, it can only be the immediate impreſſian of the conta& of the laſt hour or two, that ſamps the diſcrimination. That contact muſt needs be very efcient.°

$_A clod of a cubic inch may be ſappoſed to increaſe the ſurface acceſſible to the air tenfold by pulverization; as the ſurface of a pound of ſugar is in- creaſed by breaking it Into knobs.