when any country has a wide extent of sea to the south, and of land to the north. Thus Greenland, in lat. 60o, exhibits a more rigorous climate than Lapland, in lat. 72°. From the like cause, the north-east extremity of Asia suffers a cold almost equally intense; and the same combination of circumstances renders the climate of North America, under the same parallel, much colder than that of Europe. Nor is the influence of winds in general, and the trade-winds in particular, here to be forgot ten. Blowing from east to west across the sands of Africa, the latter produce, on its western coast, a most intense heat, much greater than is experienced on the eastern. In passing the Atlantic, they are considerably cooled; and though, in traversing South America, their temperature is again raised, yet, before reaching the opposite coast, they meet the tremendous snow-clad Andes, which stop their progress, and diffuse a wide coolness. Again, the mountain ranges of the earth not only present and retain on their sides a refreshing coolness; but, by the mighty rivers to which they give rise, diffuse a great amelioration of the temperature through extensive regions. They are particularly of this character, and give rise to the largest rivers in the torrid and burning climes of the earth. In the temperate climates, and those approaching to the poles, mountains are of moderate elevation, are almost always barren, and give rise to few considerable streams. Professor Mayer, from a comparison of observations, constructed the following empirical rule for finding the relation between the latitude and the mean temperature, in centesimal degrees, at the level of the sea. Multiply the square of the cosine of the latitude by the constant number 29, the product is the temperature. The variation of temperature for each degree of latitude is hence denoted centesimally with very great precision, by half the sine of double the latitude. that the annual accumulation would increase the average temperature of those regions. But this is not the case. The perpetual motion and currents of the atmosphere preserve a maximum temperature, which is but little varied; for, as the air of the equatorial regions becomes warmer, the northern winds have the greater tendency to rush in upon it with rapidity, and check the ex cess. But within the arctic circle,' observes an intelligent writer, another powerful agent of nature is constantly tempering the inequality of the seasons. The vast beds of snow, or fields of ice which cover the land and sea in these dreary retreats, absorb, in the act of thawing or passing again into their liquid form, all the surplus heat collected during a nightless summer. The rigor of winter, when darkness resumes her tedious reign, is likewise mitigated by the warmth evolved as congelation spreads over the watery surface.' Experiments have been made, both at home and abroad, to ascertain the comparative temperature of the earth below its surface, as compared with that of the atmosphere; and they have differed very little. "In the caves below the observatory at Paris, in 49° of north latitude, and about eighty-five feet below the surface, Fahrenheit's thermometer constantly stands between 52° and 54°, and scarcely ever varies 2°; while at the surface the difference of temperature, between summer and winter, sometimes exceeds 90°. In the salt mines at Wieliezka, near 50° of latitude, from the depth of 320 to that of 745 feet, the thermometer stands at about 50°. At Cairo, in Egypt, latitude 30°, at the bottom of Joseph's well, the depth of which exceeds 210 feet, the thermometer stands at 70°. In the mines of Mexico, at 20° of latitude, the temperature at the depth of 1650 feet, was 74°; thus it augments in approaching the equator.'-Lacroix's Geo. Physique. Mr. Leslie reports some very interesting experiments on this subject, made in the garden of his friend, Robert Ferguson, esq. of Abbots-hall, in a gravelly soil, lat. 56° 10', and proving how slow is the transmission of heat through the body of the earth. The thermometers were sunk to the depth of one, two, four, and eight feet, and the transmission from the surface appears to have been about an inch per day. The first of these thermometers never sunk lower than 33°, and indicated a mean temperature of 45°.5, which shows that the frost seldom penetrates to that depth. The nature of the soil, however, and external circumstances, must have a great influence on this penetration, as has been proved by experiment. In the same paper it is stated that, in the neighbourhood of Edinburgh, after a long continuance of rigorous weather, the frost was found to have penetrated thirteen inches into the ground in a ploughed field, but only eight inches in one piece of pasture ground, and four inches in another. But, in some of the streets of that city, the frost had descended even below two feet, so as to begin to affect the waterpipes. The greater density and solidity of the pavement had no doubt conducted the frigorific impressions more copiously downwards, while On this subject, Mr. Leslie remarks, that, If the thermometer had been sunk considerably deeper, they would, no doubt, have indicated a mean temperature of 47-70. Such is the permanent temperature of a copious spring which flows at a short distance, and about the same elevation, from the side of a basaltic, or green-stone rock. Profuse fountains and deep wells, which are fed by percolation through the crevices of the strata, furnish the surest and easiest mensuration of the temperature of the earth's crust. The body of water which bursts from the caverns of Vaucluse, and forms almost immediately a respectable and translucid river, has been observed not to vary in its temperature, by the tenth part of a degree (centigrade) through all the seasons of the year. It is therefore an object highly important for scientific travellers, to notice the precise heat of springs in favorable situations, as they issue from their rocky beds. Such choice observations would accurately fix the medium temperature of the climate. It is only requisite to exclude the superficial and the thermal springs, which are not difficult to distinguish.' See the article CLIMATE. Supplement to the Encyclopædia Britan nica. The mean temperature of the air, near the surface of the earth, has also been ascertained at various places. At Paris and Cairo it was found to correspond nearly with the numbers before stated. At St. Petersburgh in lat. 60° the mean temperature is about 39°. At Wadso, in Lapland, in 70° of latitude, it was found to be about 36°; and in the island of Mageröe, near the North Cape, the mean temperature of the year is stated, by M. Von Buch, to be nearly 32°; the mean for every month in the same situation, is inserted at page 312 of this volume. According to M. Humboldt, the hottest places are on the southern shores of the Caribbean sea, and the gulf of Guayaquil, in the great equinoxial ocean, between two and three degrees of south latitude. There the mean heat is 81.5°; and the thermometer sometimes rises to 106°. At Belbeis, in Egypt, the thermometer has risen to more than 1259 in the shade; but this was occasioned by the hot wind, denominated Sirocco. At St. Petersburgh, on the contrary, the cold is sometimes so intense as to congeal mercury. It has also been observed, at the same place, to rise above 90°. In the first number of the Edinburgh Philosophical Journal, some facts are stated by Mr. Bald apparently incompatible with the idea of the interior temperature of the earth being deducible from the latitude of the place, or the mean temperature at the surface. The following table presents at one view the temperature of air and water in the deepest coal-mines in Great Britain. Whitehaven Colliery, county of Cumberland. Air at the surface 480 feet 55 49 60 63 66 11 water at the depth of 1200 feet Distilled water boils at this depth at Do. do. at surface 74 77 25 213 210 Saussure found the lake of Geneva, at the depth of 1000 feet, to be 42°; and below 160 feet from the surface there is no monthly variation of temperature. The lake of Thun, at 370 of depth, and Lucerne at 640, had both a temperature of 41°, while the waters at the surface indicated respectively 64 and 68° 30′ Fab. Barlocci observed, that the Lago Sabatino, near Rome, at the depth of 490 feet, was only 44° 30′, while the thermometer stood on its surface at 77. Mr. Jardine has made accurate observations on the temperatures of some of the Scottish lakes, by which it appears, that the temperature continues uniform all the year round, about twenty fathoms under the surface. In like manDer, the mine of Dannemora in Sweden, which VOL. VI. presents an immense excavation, 200 or 300 feet deep, was observed, at a period when the working was stopped, to have great blocks of ice lying at the bottom of it. The bottom of the main shaft of the silver mine of Kongsberg in Norway, about 300 feet deep, is covered with perpetual snow. Hence, likewise, in the deep crevices of Ætna and the Pyrenees, the snows are preserved all the year round. It is only, however, in such confined situations that the lower strata of air are thus permanently cold. In a free atinosphere the gradation of temperature is reversed, or the upper regions are colder, in consequence of the increased capacity for heat of the air, by the diminution of the density. In the milder climates it will be sufficiently accurate, in moderate elevations, to reckon an ascent of 540 feet for each centesimal degree, or 100 yards for each degree on Fahrenheit's scale of diminished temperature. Dr. Francis Buchanan found a spring at Chitlong, in the lesser valley of Nepaul, in Upper India, which indicated the temperature of 14.7 centesimal degrees, which is 81° below the standard for its parallel of latitude, 27° 38′. Whence, 8.1 x 540 4374 feet is the elevation of that valley. At the height of a mile this rule would give about thirty-three feet too much. The decrements of temperature augment in an accelerated progression as we ascend. Ben Nevis, the highest mountain in Great Britain, stands in latitude 57°, where the curve of congelation reaches to 4534 feet. But the altitude of the summit of the mountain is no more than 4380 feet; and therefore, during two or three weeks in July, the snow disappears. The curve of congelation must evidently rise higher in summer, and sink lower in winter, producing a zone of fluctuating ice, in which the glaciers are formed. Το Baron Humboldt has stated, that the temperature of the silver mine of Valenciana in New Spain is 11° above the mean temperature of Jamaica and Pondicherry, and that this temperature is not owing to the miners and their lights, but to local and geological causes. the same local and geological causes we must ascribe the extraordinary elevation of temperature observed by Mr. Bald. He further remarks that the deeper we descend, the drier we find the strata; so that the roads through the mines require to be watered, in order to prevent the horsedrivers from being annoyed by the dust. This fact is adverse to the hypothesis of the heat proceeding from the chemical action of water on the strata of coal. As for the pyrites intermixed with these strata, it does not seem to be ever decomposed, while it is in situ. The perpetual circulation of air for the respiration of the miners must prevent the lights from having any considerable influence on the temperature of the mines. M. Humboldt has also published an admirable systematic view of the mean temperatures of different places, in the third volume of the Memoirs of the Society of Arcueil. His paper is entitled, Of Isothermal Lines (lines of the same tem erature), and the distribution of Heat over the Globe. By comparing a great number of observations made between 46° and 48° N. lat., he C found, that at the hour of sun-set the temperature is, very nearly, the mean of that at sun-rise and two hours after noon. Upon the whole, however, hethinks that the two observations of the extreme temperatures will give us more correct results. The difference which we observe in cultivated plants, depends less upon mean temperature, than upon direct light, and the serenity of the atmosphere; but wheat will not ripen if the mean temperature descend to 47.6°. Europe may be regarded, according to this distinguished traveller, as the western part of a great continent, and subject to all those influences which make the western sides of all the continents warmer than the eastern. The same difference that we observe on the two sides of the Atlantic, exists on the two sides of the Pacific. In the north of China the extremes of the seasons are much more felt than in the same latitudes in New California, and at the mouth of the Columbia. On the eastern side of North America, we have the same extremes as in China; New York has the summer of Rome, and the winter of Copenhagen; Quebec has the summer of Paris, and the winter of Petersburgh. And in the same way in Pekin, which has the mean temperature of Britain, the heats of summer are greater than those at Cairo, and the cold of winter as severe as that at Upsal. This analogy between the eastern coasts of Asia and of America, sufficiently proves, that the inequalities of the seasons depend upon the prolongation and enlargement of the continents towards the pole, and upon the frequency of north-west winds, and not upon the proximity of any elevated tracts of country. Ireland, according to Humboldt, presents one of the most remarkable examples of the combination of very mild winters with cold summers; the mean temperature in Hungary for the month of August is 71.6°; while in Dublin it is only 60-8°. In Belgium, and Scotland, the winters are milder than at Milan. The above admirable paper furnishes us with the following TABLE OF THE ISOTHERMAL BANDS, AND DISTRIBUTION OF HEAT The temperatures are expressed in degrees of Fahrenheit's thermometer; the longitudes are counted from east to west, from the first meridian of the observatory of Paris. The mean temperature of the seasons has been calculated, so that the months of December, January, and February, form the mean temperature of the winter: The mark is prefixed to those places, the mean temperatures of which have been determined with the most precision, generally, by a mean of 8000 observations. The isothermal curves having a concave summit in Europe, and two convex summits in Asia and Eastern America, the climate is denoted to which the individual places belong. Comparing the northern half of the globe with the southern, our author observes, the southern hemisphere differs considerably from the northern; but the degree of this difference has been variously stated; the coldness of the southern hemisphere, has generally been attributed to the circumstance of the sun being a shorter time on the south, than on the north side of the equator. But it probably depends more upon the greater proportion of ocean, which gives to the southern temperate zone a climate more approaching to that of a collection of islands. There is, there fore, a less accumulation of heat during the summer, and a less radiation from the land, in proportion to its less extent; and there is consequently a less current of warm air flowing from the equator towards the south pole, which permits the ice to accumulate more around it. Near the equator, and indeed through the whole of the torrid zone, the temperature of the two hemispheres appears to be the same; but the difference begins to be felt in the Atlantic about 22° of latitude; and there is a considerable difference between the mean temperature of Rio Janeiro and Havanuah, |