Had the thermometers been sunk deeper, they would undoubtedly have indicated 47.7, which is the mean temperature of the place, as is shown by a copious spring. The lake of Geneva, at the depth of 1000 feet, was found by Saussure 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 684° Fahr. Barlocci observed, that the Lago Sabatino, near Rome, at the depth of 490 feet, was only 444°, 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 20 fathoms under the surface. In like manner, the mine of Dannemora in Sweden, which 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 on Etna 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 atmosphere, 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 Nepal, in Upper India, 44.9 45.9 46.2 46.6 which indicated the temperature of 14.7 centesimal degrees, which is 8.1° below the standard, for its parallel of latitude, 27° 38′. Whence, 8.1 × 540 = 4374 feet, is the elevation of that valley. At the height of a mile this rule would give about 33 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 there. fore, during two or three weeks in July, the snow disappears. The curve of conge. lation must evidently rise higher in summer, and sink lower in winter, producing a zone of fluctuating ice, in which the glaciers are formed. In calculating the mean temperature of countries at different distances from the equator, the warmth has been referred solely to the sun. But Mr. Bald has published, in the first number of the Edin. burgh Philosophical Journal, some facts 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. A spring at the surface, and at 480 feet, 55° F. 49 60 63 66 50° F. 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. Water 180 feet down, Water 504 feet under the level of the ocean, and immediately beneath the Irish sea, 60 Difference between water at surface and bottom, 12 Teem Colliery, county of Durham. Air at pit bottom, 444 feet deep, 68 Water at same depth, 61 Difference between the mean tempe rature of water at surface = 49°, and 444 feet down, 12 Percy Main Colliery, county of Northum berland. Air at the surface, 42 Water about 900 feet deeper than the The meteorological observations now made and published with so much accuracy and regularity in various parts of the world, will soon, it is hoped, make us better acquainted with the various local causes which modify climates, than we can pretend to be at present. The accomplished philosophical traveller, M. de Humboldt, 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 temperature), and the Distribution of Heat over the Globe. By comparing a great number of observations made between 46° and 48° N. lat., he 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, he thinks, 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 as the western part of a great continent, and subject to all those influences, which make the western sides of all 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 N. W. winds, and not upon the proximity of any elevated tracts of country. Ireland, says 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. In the article Climate, Supplement to the Encyclopædia Britannica, the following very simple rule is given, for determining the change of temperature produced by sudden rarefaction or condensation of air. Multiply 25 by the difference between the density of air, and its reciprocal, the product will be the difference of temperature on the centigrade scale. Thus, if the density be twice, or one half 25° x (2-4) = 37° cent. = 67.5° Fahr. indicates the change of temperature by doubling the density or rarity of air. Were it condensed 30 times, then, by this formula, we have 749° for the elevation of temperature, or 25° (30-영이). But M. Gay-Lussac says, that a condensation of air into one-fifth of its volume, is sufficient to ignite tinder; a degree of heat which he states at 300° centigrade = 572° Fahr. (Journal of Science, vol. vii. p. 177). This experimental result is incompatible with Professor Leslie's Formula, which gives only 112.5°, for the heat produced by a condensation into one-fifth.. It appears very probable, that the climates of European countries were more severe in ancient times than they are at present. Cæsar says, that the vine could not be cultivated in Gaul, on account of its winter-cold. The rein-deer, now found only in the zone of Lapland, was then an inhabitant of the Pyrenees. The Tiber was frequently frozen over, and the ground about Rome covered with snow for several weeks together, which almost never happens in our times. The Rhine and the Danube, in the reign of Augustus, were generally frozen over, for several months of winter. The barbarians who overran the Roman empire a few centuries afterwards, transported their armies and wagons across the ice of these rivers. The improvement that is continually taking place in the climate of America, proves, that the power of man extends to phenomena, which from the magnitude and variety of their causes, seemed entirely beyond his controul. At Guiana, in South America, within five de. grees of the line, the inhabitants living amid immense forests, a century ago, were obliged to alleviate the severity of the cold, by evening fires. Even the duration of the rainy season has been shortened by the clearing of the country, and the warmth is so increased, that a fire now would be deemed an annoyance. It thunders continually in the woods, rarely in the cultivated parts. Drainage of the ground, and removal of forests, however, cannot be reckoned among the sources of the increased warmth of the Italian winters. Chemical writers have omitted to notice an astronomical cause of the progressive amelioration of the climates of the northern hemisphere. In consequence of the apogee portion of the terrestrial orbit being contained between our vernal and autumnal equinox, our summer half of the year, or the interval which elapses between the sun's crossing the equator in spring, and in autumn, is about seven days longer than our winter half year. Hence also, one reason for the relative coldness of the southern hemisphere.* Isothermal Bands, and Distribution of Heat over the Globe. 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 Feb. ruary, 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: Isothermal Names of the bands. places. Position in Mean Distribution of Heat in the different Seasons. temp. of Maximum and Minimum. Latitude. Longitude. Height in the year. Mean temp. Mean temp. Mean temp. Mean temp Mean temp. of Mean temp. of VOL. I. Nain, 37° 8′ 63° 40′ W 0 26.8° 0.4° 23.7° 48.4° 33.4° 51.8° -11.20 *Enontekies, Hospice de St. Gothard, North Cape, * Ulea, Isothernal band, from 32° to 41°. 38 Table continued from preceding page. *Buda, 47 29 16 41 494 51.0 31.0 51.0 63.2 52.4 71.6 27.6 Cambridge (U.S.) 42 25 73 23 W 0 50.4 34.0 47.6 64.4 49.8 72.8 29.8 *Paris, 48 50 0 0 222 51.0 38.6 49.2 64.6 51.4 65.3 36.0 *London, 51 30 2 25 W 0 50.4 39.6 48.6 63.2 50.2 64.4 37.8 Dunkirk, 51 2 0 2 E 0 50.6 38.4 48.6 63.8 50.9 64.8 37.8 Amsterdam, 52 22 2 30 E 0 51.6 36.8 51.6 65.8 51.6 67.0 35.4 Brussels, 50 50 2 2 E 0 51.8 36.6 53.2 66.2 51.0 67.4 35.6 *Franeker, 52 36 4 2 E 0 51.8 36.6 51.0 67.2 54.4 69.0 32.9 Philadelphia, 39 56 77 36 W 0 53.4 32.2 51.4 74.0 56.6 77.0 32.7 New York, 40 40 76 18 W 0 53.8 29.8 51.2 79.2 54.6 80.6 25.4 *Clermont, 45 46 0 45 1260 50.0 34.7 50.6 64.4 51.2 66.2 28.0 *Milan, 45 28 6 51 E 390 55.8 36.4 56.1 73.0 56.8 74.6 36.2 |