Mr. Fox appears also to have settled beyond the possibility of doubt, the long-agitated question respecting the temperature of mines, by establishing a general relation between increases of heat and depth; although the ratio cannot be reduced to any definite formula, being liable to vary with the presence of more or less water, and with the different conducting power of rocks, since mines in granite and in killas differ by several degrees of heat at the same level: yet the increase corresponds so generally with greater descents into the earth, that elevation of temperature, and not the expense, nor the difficulty of exhausting water, appears likely to oppose the final limit to the progress of mines in depth. In continuation of the same trains of reasoning and of thought, Mr. Fox has been led to investigate the important elements of variation and dip of the magnetic needle; and in pursuing these inquiries, he has invented an instrument possessed of far greater accuracy than any one previously employed, and which at this moment is in actual use, through the enlightened liberality of our own and other governments, in various and distant portions of the globe. Mr. Henwood is about to lay before the Public a Work containing the results of more extensive and scientific researches into the nature of Lodes and Fissures, than have perhaps been ever executed by any individual. Mr. Henwood is well known to geologists: I shall therefore only add what I think myself bound in duty to notice, that an original appointment in the Stanneries, and a subsequent promotion, have been bestowed on Mr. Henwood, through the medium of Her Majesty’s Duchy Officers, and principally of Sir George Harrison, in consideration of his scientific attainments, and of his desire to render these attainments available to the development of further inductions. * * * * *