foap-afhes, fo as to render the oily particles mifcible with water.The book of nature may be difplayed, to fhew that oily particles conftitute the nourishment of plants in their embryo ftate; and, by a fair inference, we may fuppofe that fomething of the fame nature is continued to them as they advance in growth. The oily feeds, as rape, hemp, line, and turnip, confit of two lobes, which, when fpread upon the furface, form the feminal leaves. In them the whole oil of the feed is contained. The moisture of the atmosphere penetrates the cuticle of the leaves, and, mixing with the oil conftitutes an emulsion for the nourishment of the plant. The fweetness of this balmy fluid invites the fly, against which no fufficient remedy has, as yet, been discovered. The oleaginous liquor being confumed, the feminal leaves decay, having performed the office of a mother to her tender infant. To perfons unacquainted with the analogy between plants and animals, this reAation will appear ftrange. Nothing, however, is more demonftrable. The leguminous and farinaceous plants keep their placentia, or feminal leaves, within the earth; in which fituation they fupply the tender germ with oily nutriment, until its roots are grown fufficiently trong to penetrate the foil.

It is ufual to talk of the falts of the earth; but chymistry has not been able to difcover any falts in land which has not been manured, though oil may be readily obtained from every foil, the very fandy ones excepted. Marl, though a rich manure, has no falts. It is thought to contain a fmall portion

of oleaginous matter, and an abforbent earth, of a nature fimilar to limeftone, with a large quantity of clay intermixed. Lime mixed with clay comes nearest to the nature of marl of any factitious body that we know of, and may be used as fuch, where it can be had without much expence. By increafing the quantity of clay, it will make an excellent compoft for a light fandy foil; but to make the ground fertile, woollen rags, rotten dung, or any oily manure, fhould be incorporated with it fome time before it is laid on. It is a received opinion, that lime enriches the land it is laid upon, by means of fupplying a falt fit for the nourishment of plants; but by all the experiments that have been made upon lime, it is found to contain no kind of falt. Its operation therefore fhould be confidered in a different light; by the fermentation that it induces, the earth is opened and divided, and, by its abforbent and alkaline quality, it unites the oily and watery parts of the fcil. It alfo feems to have the property of colle&ing the acid of the air, which it readily forms into a neutral falt, of great ufe in vegetation. From viewing lime in this light, it is probable that it tends to rob the foil of its oily particles, and in time will render it barren, unless we take care to fupport it with rotten dung, or other manures of an oily nature. As light fandy foils contain but a fmall portion of oleaginous particles, we should be extremely cautious not to overdo them with lime; unlefs we can at the fame time affift them liberally with rotten dung, woollen rags, fhavings of horn, and other manures of an animal kind. Its great

excellence,

excellence, however, upon a fandy foil, is by mechanically binding the loofe particles, and thereby preventing the liquid parts of the manure from escaping out of the reach of the radical fibres of the plants. Upon clay the effect of lime is different; for by means of the gentle fermentation that it produces, the unfubdued foil is opened and divided; the manures laid on readily come into contact with every part of it; and the fibres of the plants have full liberty to fpread themselves. It is generally faid, that lime anfwers better upon fand than clay. This obfervation will undoubtedly hold good as long as the farmer continues to lime his clay lands in a fcanty manner. Let him treble the quantity, and he will then be convinced that lime is better for clay than fand. It may be justly answered, that the profits will not admit of the expence. I agree. But then it must be underftood that it is the application, and not the nature of the lime, that fhould be called in question. Clay, well limed, will fall in water, and ferment with acids. Its very nature is changed. Under fuch agreeable circumstances, the air, rains, and dews are freely admitted, and the foil is enabled to retain the nourishment that each of them brings. In confequence of a fermentation raifed in the foil, the fixed air is fet at liberty, which, in a wonderful manner, promotes vegetation. It is the nature of lime to attract oils and diffolve vegetable bodies. Upon thele principles we may account for the wonderful effects of lime in the improvement of black moor - land. Moor earth confits of diffolved, and half-diffolved, vegetable fubVOL. XX.

ftances. It is full of oil. Lime affimilates the one and diffolves the other. Such lands, not originally worth four-pence per acre, may be made, by paring, burning, and liming, to produce plentiful crops of turnips, which may be followed with oats, barley, or grafs-feeds, according to the inclination of the owner. Thefe obfervations, however, are rather foreign to the prefent argument, to which I fhall now return.

To the univerfal principle, oil, we muft 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 demonftrable from the manner of making faltpetre in the different parts of the world. The air contains no fuch falt as perfect nitre; it is a factititious falt, 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 earth, and any fixed alkaline falt. The univerfal acid, as it is called, is attracted by these materials, and forms true nitre, which is rendered pure by means of cryftallization, and in that form it is brought to us. In very hot countries the natural earth forms a matrix for nitre, which makes the operation very short. It is obferved that nitre is moft plentifully formed in winter, when the wind is northerly: hence we may underftand the true reafon why farmers and nurserymen lay up their lands in high ridges during the winter months. The good effects of that operation are wholly attributed to the mechanical action of the froft upon the ground. Light foils, as well as the tough ones,

H

may

may be exposed in high ridges, but with fome limitation, in order to imitate the mud walls in Germany, which are found by experi. ence, to collect confiderable quantities of nitre during the winter. After faying fo much in praife of nitre, it will be expected that I fhould produce fome proofs of its efficacy, when used as manure. I muft confefs that experiments do not give us any fuch proofs. Perhaps too large a quantity has been ufed; or rather, it could not be restored to the earth with its particles, fo minutely divided, as when it remained united with the foil, by means of the chymiftry of nature. I fhall therefore confider this nitrous acid, or, as philofophers call it, the acidum vagum, in the light of a vivifying principle, with whofe operation we are not yet fully acquainted.-A curious obferver will remark, that there fubfifts a strong analogy between plants and animals. Oil and water feem to make up the nourishment of both. Earth enters very little into the compofition of either. It is known that animals take in a great many earthly particles at the mouth, but they are foon difcharged by urine and ftool. Vegetables take in the fmalleft portion imaginable of earth; and the reafon is, they have no way to difcharge it. It is highly proba ble, that the radical fibres of plants take up their nourishment from the earth, in the fame manner that the lacteal veffels abforb the nutriment from the intestines; and as the oily and watery parts of our food are perfectly united into a milky liquor, by means of the fpittle, pancreatic juice, and bile, before they enter the lacteals, we

5

have all the reafon imaginable to keep up the analogy, and fuppofe that the oleaginous and watery parts of the foil are alfo incorporated, previous to their being taken up by the absorbing veffels of the plant. To form a perfect judg ment of this, we must reflect that every foil, in a state of nature, has in itfelf a quantity of abforbent earth, fufficient to incorporate its inherent oil and water; but when we load it with fat manures, it becomes effentially neceffary to beftow upon it, at the fame time, fomething to affimilate the parts. Lime, foap-afhes, kelp, marl, and all the alkaline substances, perform that office. In order to render this operation vifible to the fenfes : Diffolve one drachm of Ruffia potafh in four ounces of water; then add one fpoonful of oil. Shake the mixture, and it will inftantly become an uniform mass of a whitifh colour, adapted to all the purpafes of vegetation. This eafy and familiar experiment is a juft reprefentation of what happens after the operation of Burn-baking, and confequently may be confidered as a confirmation of the hypothefis advanced.-Let us attend to the procefs. The fward being reduced to afhes, a fixed alkaline falt is produced. The moisture of the atmosphere foon reduces that falt into a fluid ftate, which, mixing with the foil, brings about an union of the oily and watery parts, in the manner demonftrated by the experiment. When the under ftratum confifts of a rich vegetable mould, the effects of Burn-baking will be lafting. But when the foil happens to be thin and poor, the first crop frequently fuffers before it arrives at maturity. The farmer, there

fore,

fore, who is at the expence of paring and burning a thin foil, fhould bestow upon it a portion of rotten dung, or fhambles manure, before the afhes are spread, in order to Supply the deficiency of oily particles. In confequence of this prudent management, the crop will be fupported during its growth, and the land will be preferved in health and vigour. Hitherto I have confidered plants as nourished by their roots. I fhall now take a view of them as nourished by their leaves. An attention to this part of the vegetable fyftem is effentially neceffary. Vegetables that have a fucculent leaf, fuch as vetches, pease, beans, and buck-wheat, draw a great part of their nourishment from the air, and on that account impoverish the foil lefs than wheat, oats, barley, or rye, the leaves of which are of a firmer texture. Rape and hemp are oil. bearing plants, and, confequently, impoverishers of the foil; but the former lefs fo than the latter, ow. ing to the greater fucculency of its leaf. The leaves of all kinds of grain are fucculent for a time, during which period the plants take little from the earth; but as foon as the car begins to 'be formed, they lofe their foftnefs, and diminih in their attractive power. The radical fibres are then more vigorously employed in extracting the oily particles of the earth, for the nourishment of the feed.

On the Climate of America; from

Dr. Robertion's Hiftory. 7HAT moft diftinguishes

ent laws to which it is fubject with refpect to the diftribution of heat and cold. We cannot determine precifely the portion of heat felt in any part of the globe, merely by measuring its diftance from the equator. The climate of a country is affected, in fome degree, by its elevation above the fea, by the extent of continent, by the nature of the foil, the height of adjacent mountains, and many other circumftances. The influence of these however, is, from various causes, lefs confiderable in the greater part of the ancient continent; and from knowing the pofition of any country there, we can pronounce with more certainty what will be the warmth of its climate, and the nature of its productions.

The maxims which are founded upon obfervation of our hemisphere will not apply to the other. There, cold predominates. The rigour of the frigid zone extends over half of that which should be temperate by its pofition. Countries where the grape and the fig fhould ripen, are buried under fnow one half of the year; and lands fituated in the fame parallel with the most fertile and beft cultivated provinces in Europe, are chilled with perpetual froft, which almost destroy the power of vegetation. As we advance to thofe parts of America which lie in the fame parallel with provinces of Afia and Africa, bleffed with an uniform enjoyment of fuch genial warmth as is most friendly to life and vegetation, the dominion of cold continues to be felt, and winter, though during a fhort period, often reigns with ex

the earth, is the peculiar temperature of its climate, and the differ

the American continent into the torrid zone, we fhall find the cold

prevalent in the New World extending itfelf alfo to this region of the globe, and mitigating the excefs of its fervour. While the negro on the coaft of Africa is fcorched with unremitting heat, the inhabitant of Peru breathes an air equally mild and temperate, and is perpetually fhaded under a canopy of grey clouds, which intercepts the fierce beams of the fun, without obstructing his friendly influence. Along the eaftern coaft of America, the climate, though more fimilar to that of the torrid zone in other parts of the earth, is nevertheless confiderably milder than in thofe countries of Afia and Africa which lie in the fame latitude. If from the fouthern tropic we continue our progress to the extremity of the American continent, we meet with frozen feas, and countries horrid, barren, and fcarce. ly habitable for cold, fooner than in the north.

Various caufes combine in rendering the climate of America fo extremely different from that of the ancient continent. Though the utmost extent of America towards the north be not yet difcovered, we know that it advances nearer to the pole than either Europe or Afia. The latter have 1 rge feas to the north, which are open during part of the year; and even when covered with ice, the wind that blows over them is lefs in tenfely cold than that which blows over land in the fame high latitudes. But in America the land ftretches from the river St. Laurence towards the pole, and spreads out immenfely to the wett. A chain of enormous mountains, covered with: fnow and ice, runs through all this dreary region. The

wind, in pafing over fuch an ex tent of high and frozen land, be comes fo impregnated with cold, that it acquires a piercing keenneís, which it retains in its progress through warmer climates, and is not entirely mitigated until it reach the Gulph of Mexico. Over all the continent of North America, a north-westerly wind and exceffive cold are fynonymous terms. Even in the most fultry weather, the moment that the wind veers to that quarter, its penetrating influence is felt in a tranfition from heat to cold, no lefs violent than fudden. To this powerful caufe we may afcribe the extraordinary dominion of cold, and its violent inroads into the fouthern provinces in that part of the globe.

Other caufes, no lefs remarkable, diminish the active power of heat in thofe parts of the American continent which lie between the tropics. In all that portion of the globe, the wind blows in an invariable direction from east to west. As this wind holds its courfe across the ancient, continent it arrives at the cou.tries which stretch along the western fhore of Africa, inflamed with all the fiery par icles which it hath collected from the fuitry plains of Alia, and the burning fands in the African defarts. The coast of Africa is, accordingly, the region of the earth which feels the molt fervent heat, and is expofed to the unmitigated ardour of the torrid zone. But this fame wind which brings fuch an acceffion of warmth to the countries lying between the river of Senegal and Cafraria, traverfes the Atlantic ocean before it reaches the American fhore. It is cooled in its paffage over this vaft body of

water,