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For the Commercial and Agricultural Magazine.

QMITTING(as at preſent unneceſſay) all diſquiſition about the component principles of fertility, it ſeems certain, that Fertility can only bé induced by the agency of the air. Among the wondrous modifications of this element, it would be dangerous to aſſert that, iz ſome ſhape, it is not the aual food of vegetables: to vulgar comprehenſion it may be proyed, that at leaîft it is the Carrier of fertility.—In eithér caſe the reſult would not be dif- ferent.— That air is an acceſſary to fertility is évident; becauſe vegetable earth* dug at a confiderable depth(in ſinking a well for inſtance) produces nothing without conſiderable expoſure:— becauſe, on exámining any ſe(ion+ of the Strata under us, though they are ſeldom horizontal, and fill ſeldomer according with the inequalities of the ſurface, yet that ſurface, to a certain depth, is uniformly tinged with a dark colour. If it be urged, that this alteration of colour only reſults from the decayed generations of vegetable matter through the revolutions of ages, I anſwer, that roots will follow vegetable earth much deeper thán this duſ- ky appearance; and that the roots do not penetrate deeper, becauſe the external influence of the air has not been able to endue the earth with previous fertility beneath the accuſtomed limit.— Again, the conſtant experience of the utility of fallowing land, is a proof that reiterated expoſure to the air is pradtically a cauſe of fertility—and there are ancient experiments which have de- monſtrated that the moſt ſterile Clay may be rendered moſt fertile by grinding into impalpablé powder, and expoſing it(thinly ſpread) for a twelvemonthi to the influence of the atmoſphere. —[t is alſo certain, that Air and Earth mutually tranſmit ferti- lity, like the tranſmiſſion of heat and cold in all bodies in conta 5 orfat leaſt, that there is a certain point of faturatión of fertility, beyond which expoſure tò the air conſtantly carries of the over- plus.—In the caſe of freſh dung,‘expoſure ſoon’ lowers the rertility of its ſurface down to this point of ſaturation; and the proceſs of the tranſmiſſion of ſome volatile ſubſtance is diſagree- ably ſenſible tothe noſtrils. To uſe a chemical illuſtration, one might- compare freſh dung to warm. water ſaturated with falt 5 as ſupervening cold expels all the ſalt, beyond the quantity ſolu- ble in cold wäáter; ſo ſupervening air carries from dung. a certain quantity of fertility beyond that point which may be cormpared> to the cold ſatiration of water with ſalt.[ would infer that air is an agent which continually extras fertility from all púutreſcent bodies, and ás conſtantly depoſits it on its appropriate recipient, Mould. That like all other afinities, this depoſition is far more rapid and copious on Mauld, which poíleſſes lcttle pre-

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