THE AGE OF THE EARTH AS AN ABODE FITTED FOR LIFE. 225 



qualified progress toward universal .acceptance. The body of com- 

 petent geologists to-day are probably more nearly disciples of Hutton, 

 Playfair, and Lyell than of their opponents. But such is the freedom 

 and the diversity of belief, of attitude and of method, among geologists 

 that as a class they can not be placed either here or there in the schools, 

 nor could they thirtj^-five years ago. 



But we are not primarily concerned with these matters of the schools 

 and of the past. The address presses upon our attention matters of 

 present interest and of profound importance. Referring to his former 

 wide-ranged estimate of the time of the consolidation of the earth, 

 Lord Kelvin says that "we now have good reason for judging that it 

 was more than twenty and less than forty million years ago, and 

 probably much nearer twenty than forty " (Science, May 12, p. 671), 

 and he gives qualified approval to Clarence King's estimate of twent}"- 

 four million years. In the course of the address he speaks of "strict 

 limitations," of "sure assumption," of "certain truth," and of "no 

 other possible alternative;" he speaks of "one year after freezing," 

 and even of "half an hour after the solidification;" he speaks of "a 

 crust of primeval granite," of a depth of "several centimeters," and 

 of other details of dimension and of time and of certitude so specifically 

 and so confidently that it must encourage, in the average reader, the 

 impression that the history of the earth is alread}^ passing into a pre- 

 cise science through the good ofiices of physical deduction. Is this 

 really true ? Can the uninstructed layman or the 3'oung geologist safely 

 repose confidence in these or any other chronological conclusions as 

 determinate ? Can these definite statements, bearing so much the air of 

 irrefutable truth, be allowed to pass without challenge ? What is their 

 real nature and their true degree of certitude when tested respecting 

 their fundamental postulates and their basal assumptions? 



With admirable frankness Lord Kelvin says (Science, May 12, p. 

 672): 



"All these reckonings of the history of underground heat, the details 

 of which I am sure you do not wish me to put before you at present, 

 are founded on the very sure assumption that the material of our pres- 

 ent solid earth all round its surface was at one time a white-hot liquid." 



It is here candidly revealed that the most essential factor in his rea- 

 sonings rests ultimately upon an assumption, an assumption which, to 

 be sure, he regards as "very sure," but still an assumption. The 

 alternatives to this assumption are not considered. The method of 

 multiple working hypotheses, which is peculiarlv imperative when 

 assumptions are involved, is quite ignored. I beg leave to challenge 

 the certitude of this assumption of a white-hot liquid earth, current as 

 it is among geologists, alike with astronomers and physicists. Though 

 but an understudent of physics, I venture to challenge it on the basis of 

 physical laws and ph^'sical antecedents. 

 SM 19 15 



