CHAPTER XII.
OF THE TEMPERATURE OF THE FOCAL CAVITY, AND THE INTENSITY OF THE FORCE THAT ACTED WITHIN IT.
Believing, as I do, that the few facts, supposed to be ascertained, as to subterranean temperature, at a very limited number of distant points, do not warrant any conclusion, such as has been jumped to, from them; that there is a general increment of temperature, as we descend from the surface, increasing at an average rate, of 1° Fahr. for every 50 or 60 feet additional depth, due to some all-pervading cause. Considering, that the local rates of increase, of subterraneous temperature observed, are due to local action, the nature of which remains yet to be discovered, or at least to be pointed out, and that hence, from the observed depth and temperature at one place, we cannot alone, infer anything, as to the temperature at an equal depth, in another and distant place: and considering, that even admitting the hypothesis of a pervading cause, the discrepancy of the small number of observations, varying as they do, between the wide limits of 1°, for every 30 feet, and 1° for every 90 feet, (three times as much,) or even 100 feet, is so wide, that any mean, deduced from such data, must be almost devoid of evidence;—holding such views, I myself attach but slight value, to any deductions that can be drawn, as to the tem-
