May 19, 1899. J 



SCIENCE. 



711 



vegetable matter thus produced. But it 

 seems improbable that the average of the 

 whole earth — dry land and sea bottom — • 

 contains at present coal, or wood, or oil, or 

 fuel of any kind, originating in vegetation, 

 to so great an amount as .767 of a^ ton per 

 square meter of surface ; which is the 

 amount, at the rate of one ton of fuel to 

 three tons of oxj'^gen, that would be re- 

 quired to produce the 2.3 tons of oxygen 

 per square meter of surface which our 

 present atmosphere contains. Hence it 

 seems probable that the earth's primitive 

 atmosphere must have contained free oxy- 

 gen. 



§ 43. Whatever may have been the true 

 history of our atmosphere it seems certain 

 that if sunlight was ready the earth was 

 ready, both for vegetable and animal life, 

 if not within a centurj^, at all events within 

 a few hundred centuries, after the rocky 

 consolidation of its surface. But was the 

 sun ready? The well-founded dynamical 

 theory of the sun's heat cai-efully worked 

 out and discussed by Helmholtz, Newcomb 

 and myself,* says NO if the consolidation 

 of the earth took place as long as 50 million 

 years ; the solid earth must in that case 

 have waited 20 or 50 million years for the 

 sun to be anything nearly as warm as he is 

 at present. If the consolidation of the 

 earth was finished 20 or 25 million years 

 ago the sun was probably ready, though 

 probably not then quite so warm as at 

 present, yet warm enough to support some 

 kind of vegetable and animal life on the 

 earth. 



§44. My task has been rigorously con- 

 fined to what, humanly speaking, we may 

 call the fortuitous concourse of atoms, in 

 the preparation of the earth as an abode 

 fitted for life, except in so far as I have i"e- 

 ferred to vegetation, as possibly having 

 been concerned in the preparation of an 



*See' Popular Lectures and Addresses,' Vol.1., 

 pp. 376-429, particularly page 397. 



atmosphere suitable for animal life as we 

 now have it. Mathematics and dynamics 

 fail us when we contemplate the earth, 

 fitted for life but lifeless, and try to imagine 

 the commencement of life upon it. This 

 certainly did not take place by any action 

 of chemistry, or electricity, or crystalline 

 grouping of molecules under the influence 

 of force, or by any possible kind of fortui- 

 tous concourse of atoms. We must pause, 

 face to face with the mystery and miracle of 

 the creation of living creatures. 



ADDENDUM. — MAY, 1898. 



Since this lecture was delivered I have 

 received from Professor Eoberts-Austen 

 the following results of experiments on the 

 melting-points of rocks which he has kindly 

 made at my request : 



Melting-point. Error. 



Felspar 1520° C. ±30° 



Hornblende about 1400° 



Mica 1440° ±30° 



Quartz 1775° ±15° 



Basalt about 880° 



These results are in conformity with what 

 I have said in §§ 26-28 on the probable 

 origin of granite and basalt, as they show 

 that basalt melts at a much lower tempera- 

 ture than felspar, hornblende, mica or 

 quartz, the crystalline ingredients of granite. 

 In the electrolytic process for producing 

 aluminium, now pi'acticed by the British 

 Aluminium Company at their Foyers works, 

 alumina, of which the melting-point is cer- 

 tainly above 1700° C. or 1800° C, is dis- 

 solved in a bath of melted ci-yolite at^a tem- 

 perature of about 800° C. So we may 

 imagine melted basalt to be a solvent for 

 felspar, hornblende, mica and quartz at 

 temperatures much below their own sepa- 

 rate melting-points ; and we can understand 

 how the basaltic rocks of the earth may have 

 resulted fi-om the solidification of the mother 

 liquor from which the crystalline ingre- 

 dients of granite have been deposited. 



Kelvin. 



