fore, who is at the expence of paring and burning a thin foil, fhould beftow upon it a portion of rotten dung, or fhambles manure, before the afhes are spread, in order to fupply the deficiency of oily particles. In confequence of this prudent management, the crop will be fupported during its growth, and the land will be preserved 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, peafe, 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 oilbearing plants, and, confequently, impoverishers of the foil; but the former lefs fo than the latter, owing 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 ear 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. W HAT moft diftinguishes America from other parts of the earth, is the peculiar temperature of its climate, and the differ 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 meafuring its distance 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 fhould 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 almoft deftroy the power of vegetation. As we advance to those 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 dominion of cold continues to be friendly to life and vegetation, the felt, and winter, though during a fhort period, often reigns with extreme feverity. If we proceed along. the American continent into the torrid zone, we shall find the cold prevalent in the New World extending itfelf alfo to this region of the globe, and mitigating the excess 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 obftructing his friendly inAuence. Along the eastern 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 those countries of Afia and Africa which lie in the fame latitude. If from the fouthern tropic we continue our progrefs to the extremity of the American continent, we meet with frozen feas, and countries horrid, barren, and scarcely 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 large 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 intenfely 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 weft. A chain of enormous mountains, covered with fnow and ice, runs through all this dreary region. The wind, in paffing over fuch an ex tent of high and frozen land, be comes fo impregnated with cold, that it acquires a piercing keennefs, which it retains in its progrefs 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 cause we may afcribe the extraordinary dominion of cold, and its violent inroads into the fouthern provinces in that part of the globe. Other causes, no lefs remarkable, diminish the active power of heat in those 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 countries which stretch along the western fhore of Africa, inflamed with all the fiery particles which it hath collected from the fultry plains of Afia, and the burning fands in the African defarts. The coast of Africa is, accordingly, the region of the earth which feels the most fervent heat, and is expofed to the unmitigated ardour of the torrid zone. But this fame wind which brings fuch an accelfion of warmth to the countries lying between the river of Senegal and Cafraria, traverses the Atlantic ocean before it reaches the American fhore. It is cooled in its paffage over this vaft body of water, water, and is felt as a refreshing gale along the coafts of Brafil, and Guiana, rendering thefe countries, though among the warmeft in America, temperate, when compared with thofe which lie oppofite to them in Africa. As this wind advances in its courfe across America, it meets with immenfe plains, covered with impenetrable forefts, or occupied by large rivers, marshes, and ftagnating waters, where it can recover no confiderable degree of heat. At length it arrives at the Andes, which run from north to fouth through the whole continent. In paffing over their elevated and frozen fummits, it is fo thoroughly cooled, that the greater part of the countries beyond them hardly feel the ardour to which they feem expofed by their fituation. In the other provinces of America, from Tierra Firmè weftward to the Mexican empire, the heat of the climate is tempered, in fome places, by the elevation of the land above the fea, in others, by their extraordinary humidity, and in all, by the enormous mountains fcattered over this tract. The islands of America in the Torrid Zone are either fmall or mountainous, and are fanned alternately by refreshing fea and land breezes. The caufes of the extraordinary cold towards the fouthern limits of America, and in the feas beyond it, cannot be ascertained in a manner equally fatisfying. It was long fuppofed that a vaft continent, diftinguished by the name of Terra Auftralis Incognita, lay between the fouthern extremity of America and the Antarctic pole. The fame principles which account for the extraordinary degree of cold in the northern regions of America, were employed in order to explain that which is felt at Cape Horn and the adjacent countries. The immenfe extent of the fouthern conti. nent, and the large rivers which it poured into the ocean, were mentioned and admitted by philofophers as caufes fufficient to occafion the unufual fenfation of cold, and the ftill more uncommon appearances of frozen feas in that region of the globe. But the imaginary continent to which fuch influence was afcribed, having been fearched for in vain, and the space which it was fuppofed to occupy having been found to be an open sea, new conjectures must be formed with refpect to the caufes of a temperature of climate, fo extremely different from that which we experience in countries removed at the fame distance from the oppofite pole. Accofta is the first philofopher, as far as I know, who endeavoured to account for the different degrees of heat in the old and new continents, by the agency of the winds which blow in each. Hift. Moral. &c. lib. ii. & iii. M. de Buffon adopts this theory, and has not only improved it by new observations, but has employed his amazing powers of defcriptive eloquence in embellishing and placing it in the most striking light. Some remarks may be added, which tend to illuftrate more fully a doctrine of much importance in every inquiry concerning the temperature of various climates. When a cold wind blows over land, it must in its paffage rob the furface of fome of its heat. By means of this, the coldness of the wind is abated. But if it contiH 3 RHODES HOUSE OXFORD LIBRARY nue to blow in the fame direction, it will come, by degrees, to pafs over a furface already cooled, and will fuffer no longer any abatement of its own keeness. Thus, as it advances over a large tract of land, it brings on all the feverity of intenfe froft. Let the fame wind blow over an extenfive and deep fea; the fuperficial water must be immediately cooled to a certain degree, and the wind proportionally warmed. But the fuperficial and colder water becoming fpecifically heavier than the warmer water below it, defcends; what is warmer fupplies its place, which, as it comes to be cooled in its turn, continues to warm the air which paffes over it, or to diminish its cold. This change of the fuperficial water, and fucceffive afcent of that which is warmer, and confequent fucceffive abatement of coldness in the air, is aided by the agitation caufed in the fea by the mechanical action of the wind, and alfo by the motion of the tides. This will go on, and the rigour of the wind will continue to diminish until the whole water is fo far cooled, that the water on the surface is no longer removed from the action of the wind, faft enough to hinder it from being arrested by froft. Whenever the furface freezes, the wind is no longer warmed by the water from below, and it goes on with undiminished cold. From thofe principles may be explained the feverity of winter frofts in extenfive continents; their mildness in fmail iflands; and the fuperior rigour of winter in those parts of North America with which we are beft acquainted. In the north-weft parts of Europe, the feverity of winter is mitigated by the west winds, which usually blow in the months of November, December, and part of January. On the other hand, when a warm wind blows over land, it heats the furface, which must therefore ceafe to abate the fervour of the wind. But the fame wind blowing over water, agitates it, brings up the colder water from below, and thus is continually lofing fomewhat of its own heat. But the great power of the fea to mitigate the heat of the wind or air paffing over it, proceeds from the following circumstance, that on account of the transparency of the fea, its furface cannot be heated to a great degree by the fun's rays; whereas the ground, fubjected to their influence, very foon acquires great heat. When, therefore, the wind blows over a torrid continent, it is foon raised to a heat almost intolerable; but during its paffage over an extenfive ocean, it is gradually cooled; fo that on its arrival at the fartheft fhore, it is again fit for refpiration. Thofe principles will account for the fultry heats of large continents in the torrid zone; for the mild climate of islands in the fame latitude; and for the fuperior warmth in fummer which large continents, fituated in temperate or colder zones of the earth, enjoy, when compared with that of islands. The heat of a climate depends not only upon the immediate effect of the fun's rays, but on their continued operation, on the effect which they have formerly produced, and which remains for fome time in the ground. This is the reafon why the day is warmest about two in the afternoon, the fummer warmeft about about the middle of July, and the winter coldest about the middle of January. The forefts which cover America, and hinder the fun-beams from heating the ground, are a great cause of the temperate climate of the equatorial parts. The ground, not being heated, cannot heat the air; and the leaves, which receive the rays intercepted from the ground, have not a mass of matter fufficient to abforb heat enough for this purpose. Befides, it is a known fact, that the vegetative power of a plant occafions a perIpiration from the leaves in proportion to the heat to which they are expofed; and, from the nature of evaporation, this perfpiration produces a cold in the leaf proportional to the perfpiration. Thus the effect of the leaf in heating the air in contact with it, is prodigiously diminished. For thofe obfervations, which throw much additional light on this curious subject, I am indebted to my ingenious friend, Mr. Robifon, profeffor of natural philofophy in the the univerfity of Edinburgh. opiates, volatile and cordial medicines, were therefore freely administered. Cataplafms, with the bark, opiates, and aromatics, were frequently applied externally; vinous and fpirituous ftupes were likewife ufed; but before the end of September all the toes on the affected foot were perished; and the mortification kept advancing flowly, with a livid appearance fpreading as high as the ancle, which gave me very little hopes of her recovery, cfpecially as fhe grew tired of all medicines.-But as I had fuccefsfully preferved dead flesh for many months by keeping it in fixable, or new generated air, (according to the discovery of Dr. Macbride) Dr. Macbride) I determined to try the effect it would have by an external application in this cafe, expecting the putrid effluvia of the gangrened parts (on which there is great reafon to believe the fpreading of all gangrenes depend) might be corrected, or in fome part deftroyed, by the fixable air. cataplafm was therefore directed. of fuch ingredients as I thought beft adapted to ferment by the addition of fome yeaft, as wheat, flower, honey, and water; these were mixed into a thin paste, and fet by the fire till they began to ferment, and were then applied, nearly cold, once a day, for ten days, when to my great fatisfaction the mortification was ftopped, and the putrid ftench abated; the cataplafms were continued till the dead toes became loofe, and were removed, when common digeftives and defenfative plafters were subftituted in their place; the fore began to discharge good matter, put up new flesh, and had a favour. able appearance. But accidentally H 4 A one |