OF FOREST-TREES. 



31 



pasture, that those gloomy tracts are now become healthy and habitable. CHAP. 

 It 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 unhealthful, 

 by 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-land. Moor-earth consists of dissolved, and half-dissolved vegetable substances. It 

 is full of oil. Lime dissolves the one and assimilates the other. Such lands, not originally- 

 worth 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 grass-seeds, accordino- 

 to the inclination of the owner. These observations, however, are rather foreign to the 

 present argument, to which I shall now return. 



To the universal principle, oil, we must add another of great efficacy, though very little 

 understood ; I 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 different 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 of 

 the 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 rendered 

 pure 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 is 

 observed that nitre is most plentifully formed in winter, when the wind is northerly : hence 

 we may understand the true reason why farmers and nurserymen lay up their lands in 

 high 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 as 

 tough ones, may be exposed in high ridges, but with some limitation, in order to imitate 

 the mud walls in Germany, which ai*e 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 

 confess 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 acidmn vagitm, 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 very 

 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 

 in 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 vessels absorb the nutriment from the 

 intestines ; and as the oily and watery parts of our food are perfectly united into a milky 



