Penny Blood: Serial Sensation and Working-Class Entertainment — page 76: what you’re looking at

Machine-transcribed from the original scan — historical spelling and the odd misread are preserved.

cH. vi.] HYPOTHESIS OF SOLIDITY. 59 The paper by Sir Wm. Thomson “On the Secular Cooling of the Earth’” is of great interest and well known. From his mode of viewing the manner of its solidification, he believes that it passed from the state of a liquid to that of a solid globe in a comparatively short space of time; since which period all geological events have happened. His formula expresses the rate of increase of temperature at any given depth in terms of the length of time since complete consolidation took place. The resulting curve of temperature is of such a form that, for reasonably large values of the time in question—or of the age of the habitable world—and for all such depths as the puny efforts of man can reach, it would be impossible to perceive at the present day any deviation from a uniform rate of increase. But if it were possible to reach very great depths, the rate would be found to be sensibly diminishing; and even at the centre of the earth a greater temperature need not exist than what the uniform rate of one degree I’. for 60 feet, which obtains at the surface, would bring us to at about sixty miles. The greater the value we assign to the presumed age of the world, the deeper we should have to dig before we should find the rate sensibly diminishing. Some interesting particulars concerning the relation between different assumed values for the world’s age, and the depths at which it might be practicable to detect a diminution in the rate of increase of temperature, will be found in Sir Wm. Thomson’s sectional address to the British Association, 1876. But the con- clusion at which we must arrive is, that no mine nor bore-hole is ever likely to be put down deep enough to solve the question whether the earth is solid from centre to surface or not. If ever it could be conclusively proved by observation, due allowance © being made for disturbing causes, that the rate began to diminish, that would be an argument that the earth is a solid cooling by conduction from its entire mass, and not from an internal hquid reservoir. But the shortest age that can be assigned to the world’s history is too long to allow us to expect that the depth requisite to test this question can ever be reached. 1 «Trans. Roy. Soc. Edinburgh,” Vol. xxu1, Pt. 1. p. 157; also “ Phil. Mag.,” 4th Series, Vol. xxv. p. 1, 1863, and Thomson and Tait’s ‘‘ Treatise on Nat. Phil.,” p. 711, 1867. GONG oOo SS (CO)