As the deepening progressed the heat of the bottom continued to increase, but it was soon observed in a different ratio from the calculations of the experts. After attaining the depth of fifteen thousand six hundred and fifty feet,--about the height of Mt. Blanc--which was reached early in 1864, it was noticed, for the first time, that the laws of temperature and gravitation were synchronous; that is, that the heat augmented in a ratio proportioned to the square of the distance from the surface downward. Hence the increase at great depths bore no relation at all to the apparently gradual augmentation near the surface. As early as June, 1868, it became apparent that the sinking, if carried on at all, would have to be protected by some atheromatous or adiathermic covering. Professor Tyndall was applied to, and, at the request of Lord Palmerston, made a vast number of experiments on non-conducting bodies. As the result of his labors, he prepared a compound solution about the density of common white lead, composed of selenite alum and sulphate of copper, which was laid on three or four thicknesses, first upon the bodies of the naked miners--for in all deep mines the operatives work _in puris naturalibus_--and then upon an oval-shaped cage made of papier mache, with a false bottom, enclosed within which the miners were enabled to endure the intense heat for a shift of two hours each day. The drilling was all done by means of the diamond-pointed instrument, and the blasting by nitro-glycerine from the outset; so that the principal labor consisted in shoveling up the debris and keeping the drill-point _in situ_. Before proceeding further it may not be improper to enumerate a few of the more important scientific facts which, up to the 1st of November of the past year, had been satisfactorily established. First in importance is the one alluded to above--the rate of increase of temperature as we descend into the bowels of the earth. This law, shown above to correspond exactly with the law of attraction or gravitation, had been entirely overlooked by all the scientists, living or dead. No one had for a moment suspected that heat followed the universal law of physics as a material body ought to do, simply because, from the time of De Saussure, heat had been regarded only as a force or _vis viva_ and not as a ponderable quality.