OF FOREST-TREES.

pasture, that those gloomy tracts are now become healthy and habitable, chapIt is not to be imagined how many noble seats and-dwellings in this na-tion of ours (to all-appearance well situated) are for all that unhealthfuljby reason of some grove or hedge-rows of antiquated dotard trees (nay,sometimes a single tuft only, especially the falling autumnal leaves neg-lected to be taken away) filling the air with musty and noxious exhala-

moor-Iand. Afoor-earth consists of difsolved, and half-difsolved vegetable substances. 1 1is full of oil. Lime dissolves the one and afsimilates the other. Such lands, not originallyworth fourpence per acre, may be made by paring, burning, and liming, to produce plen-tiful crops of turnips, which may be followed by oats, rye, barley, or grals-seeds, according-to the inclination of the owner. These observations, however, are rather foreign to thepresent argument, to which I shall now return.

To the universal principle, oil, we must, add another of great efficacy; though very hitler,understood ; L mean the nitrous acid of the air. That, the air does contain the-rudiments'of nitre, is demonstrable from the manner of making salt-petre in the diiferent parts of the'--world. The air contains no such salt as perfect nitre; it is a factitious salt, and is made •by the nitrous acid falling upon a proper matrix. The makers of nitre, form that matrix ofthe rubbish of old houses, fat putrescent earth, and any fixed alkaline.salt.. The universal-acid, as it is called, is attracted by these materials, and forms true nitre, which is renderedpure by means of crystallization, and in that form it is brought to us. In very hot coun-tries the natural earth forms a matrix for nitre, which makes the operation very short. It isobserved that nitre is most plentifully formed in winter, when the wind is northerly: hencewe may understand the true reason why farmers and nurserymen lay up their lands inhigh ridges during the winter months.. The good effects of that operation are in general,attributed to the mechanical action of the frost, upon the ground. Light soils, as well astough ones, may be exposed in high ridges, but with some Imitation, in order to imitatethe mud walls in Germany , which .are found, by experience, to collect considerable quan-tities of nitre during the winter. After saying so much in' praise of nitre, it will be ex-pected that I should produce some proofs of its efficacy, when used as manure. I must,confefs that experiments do not-give us any such proofs. Perhaps too large a quantity has-been used or rather, it could not be restored to - the earth with, its particles so minutely,divided, as when it remained united with the soil, by means-of the chymistry of Nature.

I.shall therefore consider this nitrous acid, or, as philosophers call it, the acidum . vagum, in

the light of a vivifying principle, with, whose operation we are not yet-fully acquainted-

A curious observer will remark,, that there subsists a strong.analogy between plants and .animals. Oil and water seem to make up the nourishment, of both. . Earth enters verv.,little into the composition ,of either. It. is known that animals take in a great many earthy-particles at the mouth, but they are soon discharged by urine and..stool... Vegetables take^m the smallest portion imaginable of earth; and the reason is, they have no way to dis-charge it. It is highly probable, that the radical fibres of.plants- take up their nourishment'.'from the earth in the same manner that the lacteal velseis absorb the nutriment from the.intestines ; and as the oily and watery parts of our food.are perfectly united into a milky.