324 Eevieivs—Capf, C. E. Dutton— 



These two indications are quite concordant, and we have no other 

 tangible evidence bearing upon the subject, either one way or the 

 other. Of his own view Mr. Mallet has produced no proof what- 

 ever, but assumes it at once, because it suits his hypothesis. 

 Although the burden of proof is clearly with him, an appeal to it 

 may be regarded as indecisive. Nor is this necessary : for his 

 argument may be more directly assailed. If it be sought to 

 invalidate the application of Baron Fourier's theorem by attempt- 

 ing to show that the heat found in mines and wells is due in any 

 appreciable degree to the work of a subsiding crust, the effort must 

 fail. For let us suppose that the earth has dissipated at least one- 

 fourth of its aboriginal heat. If it has dissipated more, then the 

 argument will be stronger. Then, neglecting for a moment the 

 heat arising from the subsiding crust, and all other secondary or 

 extraneous additions, the rate of increase of temperature with depth 

 would be in portions near the surface not far from one degree F. 

 per 1000 feet of descent. But the mean observed rate of increase 

 is some seventeen times greater than this ; and, if the observed rate 

 is due to the secondary cause, then we should have the remarkable 

 conclusion forced upon us, that only the seventeenth part of the 

 heat radiated into space is original, the remainder being generated 

 by the work of its sinking crust ; which is quite impossible. If a 

 more advanced stage of cooling than one-fourth be assumed, then 

 the impossibility becomes all the more conspicuous : if the cooling 

 be much less advanced than one-fourth, the quantitative basis of Mr. 

 Mallet's hypothesis disappears. If the proposed modification proved 

 anything, it would prove that the subsiding crust could generate an 

 enormously greater quantity of heat than the earth originally 

 possessed; whereas we know that, in any case, the quantity so 

 generated must be far less. The applicability of Fourier's theorem 

 to the cooling earth cannot be impaired therefore by the proposed 

 objection. The result of its application is the conclusion, that the 

 secular cooling of the earth is still in its earlier stages ; that the 

 cooled portion is comparatively speaking only skin-deep ; and that 

 the nucleus is very nearly as hot as ever. If this conclusion is ever 

 weakened, it will be by the effect of laws and processes which are 

 at present unknown. 



We have quoted the above paragraph in full, because it expresses 

 Captain Dutton's conclusions upon a question that has been much 

 debated of late, yet rarely with so much clearness. He goes on to 

 say that the foregoing argument was first presented by the Eev. 

 Osmond Fisher, of Cambridge (England), and subsequently by 

 himself without any knowledge of Mr. Fisher's analysis. The 

 conclusions reached were identical. The writer referred to cer- 

 tainly did apply the results of Sir William Thomson's investiga- 

 tion to determine the amount of inequalities of the earth's surface, 

 which might be produced by the shrinking due to cooling, and found 

 it to be very far too small to account for those which exist. But he 

 did not directly apply this result to the refutation of Mr. Mallet's 

 theory, as Captain Dutton has done. He approached that question in 



