Septembeb 7, 1906.] 



SCIENCE. 



303 



with many modern speculations on the cause 

 of earthquakes, which ascribe these tremors 

 to the slipping of rocks. My unpublished 

 inquiry indicates that the true cause is very 

 different. I regret that I am not yet able to 

 give the chain of reasoning by which this re- 

 sult is established, but I may say that it is 

 shown that one common cause underlies earth- 

 quakes, volcanoes, formation of mountains 

 and islands, the elevation of plateaus, the 

 feeble attractions of mountains noticed in 

 geodetic operations, and the formation of 

 great sea waves which frequently accompany 

 violent earthquakes. All these phenomena 

 are proved to be intimately connected, and I 

 liave shown that they depend upon a single 

 cause, and that the earth's crust is underlaid 

 by a fluid substratum in which the forces 

 arise that disturb the crust. 



It is nearly always assumed that changes 

 in the earth's crust are due to secular cooling, 

 hut is that really so? When the truth comes 

 to be known, I think it will be found that we 

 have all been working on a false premise; a 

 jnisleading hypothesis. In Astronomische 

 NachricTiten, 4104, I have shown that rigidity 

 prevents circulation, and, therefore, secular 

 cooling would be confined almost entirely to 

 the surface layers. Fisher and others have 

 shown that the shrinkage due to the cooling 

 of the crust is quite inadequate to account for 

 the mountain folds observed upon the earth, 

 which my researches show to depend on an 

 entirely different cause. 



Dr. Thomson is quite right in pronouncing 

 against radium as a cause of volcanic action. 

 The Hon. E. J. Strutt, of Cambridge, has 

 shown that radium is very abundant in the 

 rocks of the earth's crust, such as granite. 

 If, therefore, we imagine radium to be the 

 source of volcanic outbreaks, we should ex- 

 pect abundant eruptions to occur in all coun- 

 tries underlaid with granite — the United 

 States, Europe, Asia, Africa, Australia, Bra- 

 zil — which is contrary to observation. The 

 well-known distribution of volcanoes invali- 

 dates the radium theory completely. 



The Hon. R. J. Strutt, from his radium 

 investigations, concludes that the internal 



temperature of the moon exceeds that of the 

 earth. The observed low temperature of the 

 lunar surface, however, contradicts this hy- 

 pothesis, and thus we must be very cautious 

 about ascribing too much to radium. The 

 best experimental evidence available is that 

 radium is a temporary form of matter, the 

 energy of which must be renewed from other 

 sources at intervals of 20,000 years, and thus 

 it may play only an inappreciable part in the 

 physics of the universe. • So far, there is no 

 evidence that it is an important cosmical 

 agency. 



The great forces which have most pro- 

 foundly modified the world will be found to 

 be familiar ones, which are overlooked mainly 

 because they are so simple and so near at 

 hand. 



T. J. J. See. 



U. S. Naval Observatory, 



Mare Island, California, , ^^^^ >' 



August 16, 1906. ; ^; ""^ ^ 



THE NATURE OP EVOLUTION. 



On returning from Central America I find- 

 Dr. E. A. Ortmann's paper in Science of 

 April 27 under the heading < Dr. O. E. Cook's 

 Conception of Evolution.' Lest the use of 

 this label deceive any possible patrons of the 

 genuine preparation, it may be desirable to 

 point out that the most important ingredients 

 have been omitted, so that the peculiar virtues 

 of my evolutionary eye-water are entirely lost ! 



To suppose that progress in evolutionary 

 knowledge can be made by the arbitrary lim- 

 itation and redefinition of terms would imply, 

 of course, a very shallow and merely meta- 

 physical apprehension of the concrete data of 

 the subject. Nevertheless, conceptions of evo- 

 lution have to be communicated through the 

 medium of language, and language has to be 

 explicit if it is to convey definitely outlined 

 ideas. When there is a practical reason for 

 doing so, a term may be used in a special 

 sense, subject only to the obvious desirability 

 that linguistic changes, whether of new words 

 or of modified meanings, be kept down to the 

 lowest possible limits which will serve the pur- 

 poses of clear exposition for the subject in 

 hand. 



