the bottom of the Poldice mine, which is 176 fathoms deep at 90° or 100°. As this is higher than the warmth of the human body, Mr. Fox justly observes that it amounts to a proof that the increased temperature cannot proceed from the persons of the workmen employed in the mines. Neither can the warmth of mines be attributed to the condensation of the currents of air which ventilate them. Mr. Fox, whose opinion is of high authority in these matters, states that, even in the deepest mines, the condensation of the air would not raise the temperature more than 5° or 6°; and that, if the heat could be attributed to this cause, the seasons would sensibly affect the temperature of mines, which it appears they do not where the depth is great. Besides, the Cornish mines are generally ventilated by numerous shafts opening into the galleries from the surface or from a higher level. The air circulates freely in these, descending in some shafts and ascending in others. In all cases Mr. Fox found that the upward currents are of a higher temperature than the descending currents; so much so, that in winter the moisture is often frozen in the latter to a considerable depth; the circulation of air, therefore, tends to cool the mine instead of increasing the heat. Mr. Fox has also removed the objections arising from the comparatively low temperature of the water in the shafts of abandoned mines, by showing that observations in them, from a variety of circumstances which he enumerates, are too discordant to furnish any conclusion as to the actual heat of the earth. The high temperature of mines might be attributed to the effects of the fires, candles, and gunpowder used by the miners, did not a similar increase obtain in deep wells, and in borings to great depths in search of water, where no such causes of disturbance occur. In a well dug with a view to discover salt in the canton of Berne, and long deserted, M. de Saussure had the most complete evidence of increasing heat. The same has been confirmed by the temperature of many wells, both in France and England, especially by the Artesian wells, so named from a peculiar method of raising water first resorted to in Artois, and since become very general. An Artesian well consists of a shaft a few inches in diameter, bored into the earth till a spring is found. To prevent the water being carried off by the adjacent strata, a tube is let down which exactly fills the bore from top to bottom, in which the water rises pure to the surface. It is clear the water could not rise unless it had previously descended from high ground through the interior of the earth to the bottom of the well. It partakes of the temperature of the strata through which it passes, and in every instance has been warmer in proportion to the depth of the well; but it is evident that the law of increase cannot be obtained in this manner. Perhaps the most satisfactory experiments on record are those made by MM. Auguste de la Rive and F. Marcet during the