672 



SCIENCE. 



[N. S. Vol. IX. No. 228. 



nection with the United States Geological 

 Survey, a very important series of experi- 

 mental researches on the physical proper- 

 ties of rocks at high temperatures was com- 

 menced by Dr. Carl Barus, for the purpose 

 of supplying trustworthy data for geolog- 

 ical theory. Mr. Clarence King, in an 

 article published in the American Journal of 

 Science,^ used data thus supplied, to esti- 

 mate the age of the earth more deiinitely 

 than was possible for me to do in 1862, with 

 the very meagre information then available 

 as to the specific heats, thermal conduc- 

 tivities, and temperatures of fusion of rocks. 

 I had taken 7000° F. (3781° C.) as a high 

 estimate of the temperature of melting rock. 

 Even then I might have taken something 

 between 1000° C. and 2000° C. as more 

 probable, but I was most anxious not to 

 underestimate the age of the earth, and so I 

 founded my primary calculation on the 

 7000° F. for the temperature of melting 

 rock. We know now from the experiments 

 of Carl Barusf that diabase, a typical basalt 

 of very primitive character, melts between 

 1100° C. and 1170°, and is thoroughly 

 liquid at 1200°. The correction from 3871° 

 C. to 1200° or 1/3.22 of that value, for the 

 temperature of solidification, would, with 

 no other change of assumptions, reduce my 

 estimate of 100 millions to 1/(3.22)' of its 

 amount, or a little less than 10 million 

 years; but the effect of pressure on the 

 temperature of solidification must also be 

 taken into account, and Mr. Clarence King, 

 after a careful scrutiny of all the data given 

 him for this purpose by Dr. Barus, con- 

 cludes that without further experimental 

 data ' we have no warrant for extending 

 the earth's age beyond 24 millions of 

 years.' 



§ 19. By an elaborate piece of mathe- 



■* ' On the Age of tie Earth,' Vol. XLV., January, 

 1893. 



tPAiV. 3Iag. 1893, first half-year, pp. 186, 187, 

 301-305. 



matical bookkeeping, I have worked out 

 the problem of the conduction of heat out- 

 wards from the earth, with specific heat in- 

 creasing up to the melting point as found 

 by Eiicker and Eoberts-Austen and by 

 Barus, but with the conductivity assumed 

 constant ; and, by taking into account the 

 augmentation of melting temperature with 

 pressure in a somewhat more complete 

 manner than that adopted by Mr. Clarence 

 King, I am not led to differ much from his 

 estimate of 24 million years. But, until we 

 know something more than we know at 

 present as to the probable diminution ot 

 thermal conductivity with increasing tem- 

 perature, which would shorten the time 

 since consolidation, it would be quite inad- 

 visable to publish any closer estimate. 



§ 20. 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 

 present solid earth all round its surface was 

 at one time a white-hot liquid. The earth 

 is at present losing heat from its surface 

 all round from year to year and century to 

 century. We may dismiss as utterly un- 

 tenable any supposition such as that a few 

 thousand or a few million years of the 

 present regime in this respect was pi-eceded 

 by a few thousand or a few million years of 

 heating from without. History, guided by 

 science, is bound to find, if possible, an an- 

 tecedent condition preceding every known 

 state of affairs, whether of dead matter or 

 of living creatures. Unless the earth was 

 created solid and hot out of nothing, the 

 regime of continued loss of heat must have 

 been preceded by molten matter all round 

 the surface. 



§ 21. I have given strong reasons* for 

 believing that immediately before solidifica- 

 tion at the surface, the interior was solid 



* On the Secular Cooling of the Earth, Vol. III. 

 Math, and Phys. Papers, R 19-33. 



