On the Age of the Earth

Abstract

IN reference to Lord Kelvin's letter (NATURE, January 3, p. 227), he will, no doubt, presently communicate with you on the results of measurements which he is making on conductivity and temperature in rocks. I do not wish to forestall him by referring at present to his more recent correspondence with me. Three weeks ago I sent him the solution of the problem of a cooling sphere whose conductivity k and volumetric capacity c are any functions whatsoever of the temperature v, but which are always proportional to one another. As Mr. Heaviside had been writing to me, and had shown me that under certain circumstances the differential equation became linear, and as I had used his operators much as he himself uses them, I cannot say to what extent I can claim credit for the work. I now venture to send you the more general case.