Penny Blood: Serial Sensation and Working-Class Entertainment — page 88: what you’re looking at

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

CH. VI. ] HYPOTHESIS OF SOLIDITY. 71 instead of 7000°, and the corresponding value for ¢, viz. 33,000,000 years’, the result becomes surprisingly small in- deed. For then 2ke would be about 149 feet. In this case 2a would be about 100 miles. It is however important to remark that as far as our determi- nation of the average height of the inequalities is concerned the conductivity of the rock 1s not required to be known, nor yet the time since solidification took place, but only the value of the constant a, which is known at once from the rate of increase of temperature near the surface and the temperature of solidi- fication. Because (see Sir William Thomson’s paper) dv V_4% 2 “5, de” Tra ada” hence near the surface, putting 2 = 0, 1 20 | 51 oar’ and therefore, when V= 7000", . 102 _ 402830. Jr But although the actual value of the conductivity is not involved, nevertheless the equations assume that its average value continues constant, as indeed it 1s found to do by obser- vation near the surface’. 1 To find the time since the earth was all melted, on the supposition that it has cooled as a solid, and that the temperature was then 4000° F. as deter- mined for slag in Mr Mallet’s experiments, x dv V 1 i daa Jwn tt a =a 4AS 1600¢ Taking 7 of 1° as the rate of increase of temperature at the surface where 2=0, we get from the above t= 83 millions of years. 2 Principal Forbes found that the conductivity of iron diminishes as the temperature increases. Tait’s ‘‘Recent Advances in Ph. Science,” 2nd ed., GONG oOo SS (CO)