able Ocal of my communication to the same Society, and which has been published in the second volume of their Transactions. The substance of this communication I conceive it necessary in this place to detail, as I shall have frequent occasion to refer to it. I have since collected some additional facts which, I conceive, will tend to strengthen very materially the opinion I originally advanced. These shall follow in the second place, reserving any comments for the conclusion. As it is only by comparing the different results of the experiments of individuals that the truth, or an approximation to it, can be elicited, I conceive too much attention cannot be paid to the manner in which these experiments are conducted. With respect to the temperatures now given, where there has been any degree of uncertainty in the result, they have been taken twice or thrice in the same spot, by different methods, such as burying the thermometer in the earth, or rock of the gallery, in mud or water, lodging in the gallery, in the full stream of water flowing from the veins, by allowing it to remain 15 or 20 minutes during each observation, and by the correspondence of two or more thermometers at the same time. I have lately ascertained the temperature of three levels which have been driven from Crenver directly under the deepest level in Trenoweth (the mine alluded to in the Annals for April, p.416). At the depth of 124 fathoms below the adit level, or 936 feet from the surface, it was 57°; at 984 feet, 58°; at 1044 feet, 58o. Five months before, when the miners were at work in the last mentioned level, the temperature was 68o. In Oatfield copper mine in May, 1822, the temperature of the air in the engine shaft at the adit level was 61°. of 1092 feet from the surface, it was 77°, and at 1272 feet, and 480 feet east of the shaft, 78°; at 1332 feet, and 600 feet east' of the shaft, it was 81°; but at the same level, 360 feet west of the shafts, it was only 78° : neither of these spots were working places; but the latter was more contiguous to them than the other. At the depth of 1392 feet, in a working part 72 feet east of the shaft, it was 80°; and only 24 feet deeper, 180 feet west of the shaft, in a confined end, it was 85°. Here the water issuing in considerable streams from two small veins, at the bottom of the gallery, a few feet apart, indicated the different temperatures of 82o and 861°. Since the temperature of the different parts of this mine has been taken, the pumps have been drawn up from the deepest part, and the shaft, below the depth of 182 fathoms from the surface, has been for some months full of water. At this level, the temperature was previously 77o, but a few months afterwards (in Sept. last), when the water had risen to the level, its temperature, a few feet below its surface, was 69°; and at the depth of 72 feet in the water, it was 71o. A fortnight after this, I repeated the experiment, and found the temperature, a few feet At the depth : a a below the level, 66° ; and at 12 fathoms, as before, deep in the water, 67°; it having cooled 3° in a fortnight, and 11° since its admission into the shaft. In Crenver copper mine, very little work has been done for a great while. At 300 feet, and 300 feet east of the engine shaft, the temperature was 55°; at 432 feet deep, 56°; at 492 feet, 61°; at 617 feet, 62°; at 672 feet; 64°; at 732 feet, 64° in the shaft; but in a gallery 360 feet east, only 60°; at 792 feet, 63 in the shaft; but 1200 feet east of it, only 61°, at 852 feet, 62° ; but at 180 feet west, it was 64°; and at 1200 feet west, it was 68o. Huel Abraham is on the same lode as Trenoweth, Crenver, and Oatfield; and is, in almost every part, in full work. At 1332 feet below the surface, the temperature was 84o. At 1392 feet deep, at the extremity of the level, on a Monday morning, before the workmen had returned to labour, and where a machine was erected for blowing fresh air to the miners, the thermometer stood at 90°; but a few days afterwards, when a communication had been formed, it fell to 86o. At the depth of 1452 feet, it was, in one gallery, 84°; and in another (the only spot where there were no workmen), it was 86o. I shall now mention the result of some experiments, to ascertain the temperature of the water, at different depths, in miner which have been long abandoned. Herland copper mine, in Gwinear, has ceased working (except above the adit), 15 years. On the 28th May, 1822, while the temperature in the shade at the surface was 64°, and in the sun 74°, I found that of the water running through the adit, 32 fathoms deep, 52°; as we approached the engine shaft, it was increased to 53°; and on sinking two self-registering thermometers, properly secured in a box with iron weights, the temperature, at the depth of 10, 20, 40, 60, and 100 fathoms in the water, and 792 feet from the surface, was uniformly 54o. In another shaft in this mine, 360 feet north-west of the great engine shaft, the water running through the adit was 54°; and at 10, 20, and 40 fathoms deep, 56o. On the 8th of June, 1822, I visited Huel Poel and Huel Rose lead mines near Helston. In the former, the temperature of the water, at 10 and at 20 fathoms deep, was 53°, In another shaft it was precisely the same. In Huel Rose, the water in the engine shaft was, at 60 feet deep, 53 °; at 120 feet, 531°; at 240 feet, 534°; and at 300 feet, only 53o. The time allowed for the thermometer to remain at the different depths (except the last) was 10 minutes, which, perhaps, was scarcely long enough. In Huel Alfred (visited in July, 1822), the temperature of the water in the adit, 18 fathoms below the surface, was 56°; and at the several depths of 60, 120, 240, 360, 600, and 672 feet of water, or 780 feet from the surface, it was uniformly the same, a Relistian mine in Gwinear (visited on the same day) is reported to have been, when at work, much hotter than mines in general ; but I found the water in the adit, 25 fathoms deep, only 55°; and at 10, 20, and 25 fathoms below the adit, it was still the same. Huel Ann an old tin mine, 353 feet above the level of the sea, is situated in granite, and is on the saine lode as Huel Trumpet, in the parish of Wendron. This mine has not been wrought for the last 20 years, but is to be immediately reworked ; and men have , consequently been employed to open that part of the mine above the adit. On uncovering a shaft, I found that I could drop 120 fathoms perpendicular. This I did with half a hundred weight, to which was affixed a common botile properly corked, sealed and secured, so that with a small cord affixed, the cork was withdrawn after a lapse of a few minutes. The water thus drawr. from the bottom was of the temperature of 52°, and a pint of it left only a residuum of l, gr. I then sunk a day and night thermometer properly secured, as in my former experiments, and found the temperature at the depth of 30, 60, 120, 240, and at 720 feet, or the bottom of the mine, uniformly of the temperature of 52o. The adit is 14 fathoms, thus making the depth from the surface 804 feet; and the thermometer was allowed to remain at the bottom of the water for four hours. On repeating my experiments on the temperature of the water in the Herland mine, I found the heat at all depths, as before stated, viz. 64° in the old engine shaft, and 56° in another about 60 fathoms distant; and in a third, not before tried, the water was only 52o. I was given to understand by Capt. S. Grose, who accompanied me, that all these shafts extended to nearly the same depth. This circumstance I conceive rather remarkable, and clearly proves the operation of different causes of temperature in a very circumscribed portion of ground. At Huel Franchise, a tin and copper lode in the parish of Wendron, 313 feet above the level of the sea, and parallel with Huel Trumpet. The water in this mine, which has ceased working for about two years, was in November last at the bottom, or 188 feet in depth, 51°. Huel Nancy is on the same lode, but half a mile east of the latter mine. This mine is about 200 feet deep, and indicated at all depths 51°; while the temperature in the shade at the surface was 65o. This mine has stopped more than 20 years. In making my experiments with the registering thermometer, in order to obtain as correct results as possible, I always reduce the degree of the mercurial one to about the freezing point, by sprinkling its bulk with ether, and by raising the spirit one with my tongue, bringing the indices to correspond before each immersion, There appears to be little or no difference in the mean temper а ature of the same spot in a deep and confined part of a mine at work, in summer or winter; or at least the miners are not sensible of any. Capt. W. Teague assures me, that he has often met with ice in great abundance in Tin-Croft mine, at the depth of 318 feet below the surface; and in such quantities that the ladders have been impassable; deep crevices in the walls have been completely filled, and icicles hanging abundantly around him. As liquid and aeriform bodies convey heat on a different principle from that observed in solids, viz. by an actual change in the situation of their particles, instead of an augmentation of their bulk, as in solids, in proportion to the absorption of caloric, it may not be deemed irrelevant to explain this principle, and apply it to the circumstances of the water in a relinquished mine, and show how the whole water becomes of an uniform temperature. Supposing the greatest temperature is at E, the bottom A of the mine, and the whole becomes filled with water by infiltration from the surface. This water must bring with В. it a medium temperature of the surface, and the different strata of earth through which it has passed, which, if of с less heat than that possessed by the earth at the bottom, will of course become heated to the same degree; it, D therefore, is expanded, and, becoming specifically lighter, ascends to the surface, and is replaced by a colder portion E from above. This, in its turn, becomes heated and dilated, and gives way to a second colder portion; and thus the process goes on as long as the fluid is capable of imbibing heat. Therefore, whether the thermometer is sunk to A, B, C, D, or E, in an old mine, it must be found of an equable degree. M. de Mairan asserts, that the rigour of the cold of winter is tempered by the heat imparted to the atmosphere by the earth itself, which heat, probably possessed from its origin, is preserved and renewed by the incessant influence of the sun, to which one half of its surface is constantly exposed.. Admitting this fact, the temperature of the atmosphere must depend on the capacity of the earth for receiving and retaining heat, and for communicating it to the surrounding medium. But as the earth is composed of land and water, it should be considered that the capacities of these constituent parts, for receiving heat are very different. Land, particularly when dry, receives heat from the sun's rays very readily, but transmits it through its own substance to great depths very slowly; and, on the other hand, water, by reason of its transparency, receives heat very slowly, but diffuses what it receives more readily. Dr. Hales found that in the month of August, 1724, when the air and the surface of the earth were both at 88°, a thermometer placed only two inches below the surface of the earth stood at 85°; another, 16 inches under the surface, indicated 70°; and a 1 1 *| 1 B third, 24 inches deep, stood at 68o. The last two thermometers From these experiments, it may be inferred that the surface of Marriotte's experiments furnish nearly similar results to those M. Van Swinden has observed, that the greatest cold, and Such facts tend to prove that the heat of the earth does not increase as we descend into it; but at the greatest depths, it is nearly the same as the mean annual temperature of the latitude. The following table of temperatures, taken by myself, will be convenient for a general reference, distinguishing the mines at work from those long since abandoned; and the medium in which the temperatures were taken: a |