464 0. Fisher — Rigidity not to he relied upon 



Art. LIV. — Rigidity not to he relied upon in estimating the 

 EartKs Age ; by Osmond Fisher, Cambridge, England. 



It is impossible not to admire the ingenious argument by 

 which Mr. Clarence King* reasons that, assuming the earth 

 to be rigid, the temperature gradient must be such that, 

 within the first few hundred miles at least, it cannot inter- 

 sect the curve which he uses to express the fusibility of 

 igneous rock under the pressure corresponding to the depth. 

 Placing this before his mind, he was led to obtain an examina- 

 tion of the rock diabase at high temperatures to be made by 

 Dr. Barus ;f and we owe a debt of gratitude to both these 

 gentlemen for an interesting addition to our scanty store of 

 knowledge of this obscure class of subjects. 



On comparing Dr. Barus's results with those obtained by 

 Professors Pucker and Roberts-Austen for the dolerite of 

 Rowley Regis, we are struck by the considerably higher value 

 of the melting point of diabase, which is about 1170° C, 

 whereas that of the dolerite was found to be under 920° C. 

 On the other hand, Dr. Barus makes the latent heat of fusion 

 of the diabase to be 24, whereas that of the dolerite is 49 \\ 

 thus the latent heat of the rock which has the lower melting- 

 point is more than double that which has the higher. 



When, however, by means of the above considerations Mr. 

 King endeavors to fix a limit within which the age of the earth 

 must lie, it is clear that the rigidity of the earth must be first 

 established. In proof of this he refers to the " unshaken re- 

 sults of Ld. Kelvin (Sir W. Thomson) and Professor G. H. 

 Darwin," and to "the further arguments for rigidity advanced 

 by Professor S. Newcomb§ from the data of the lately ascer- 

 tained periodic variation of terrestrial latitude, as together 

 warranting a firm belief in the rigid earth." 



I hope it will not be thought presumptuous if I endeavor 

 to point out what these authorities have really determined. 

 And first of Professor S. Newcomb's discussion of the periodic 

 variations of latitude. 



On referring to the article in the monthly notices of the 

 Royal Astronomical Society, § it will be found that he proposes 

 two modes of explaining the phenomena. The first hypothesis 

 which he examines is an elastic yielding of the solid earth, and 

 he comes to the conclusion, that the phenomena recently dis- 



*This Journal, Jan., 1893. f Ibid, Jan., 1S92. 



X Appendix to the writer's "Physics of the Earth's Crust," 2d ed., p. 18, 1891. 

 See also the account of the experiments, Phil. Mag., Oct.. 1891. 

 §For March, 1892. 



