At surface, in June, 59 118 feet deep 64½ 480 “ 68 840 “ 69½ 1144 “ 79 _December._ At the surface air 50 120 feet air 57 600 “ air 66 ---- “ water 64 962 “ air 70 ---- “ water 74 1200 “ air 78 ---- “ water 78 M. Humboldt obtained analogous results in many mines in South America. The evidence in favor of a _perpetually increasing temperature as you descend into the earth_, and a _higher temperature formerly at the surface of the earth_, is increasing daily. _See the conclusion of this paper._ 3. There is yet a third theory, founded on _voltaic energy_, or _galvanism_ and _electricity_. The application of these agents to the production of volcanic action, had occurred to me, before I met with the “Outline of the course of Geological Lectures, given in Yale College,” by Professor Silliman, from which the following extract is made. I had not regarded their application in the same manner as he has explained it. Indeed, my thoughts on the subject had not assumed any definite direction. I shall transcribe from his “Outline,” pp. 118-19, inserted in “Bakewell’s Introduction to Geology, first American Edition.” “Whatever we may think of the hypothesis now detailed, may we not suppose, with sufficient probability, that those voltaic powers which we _know_ to exist--whose action we can command, and whose effects having been first observed within the memory of the present generation, now fill us with astonishment, are constantly active in producing the phenomena of earthquakes and volcanos?