344 Mr. 0. Chree on some Applications of 



plastic state to which he refers, as seems almost certain from 

 the context, he must have formed an extremely low estimate 

 of what strains a solid can stand. 



In the same passage Mr. Blytt refers to Mr. Peirce *, Sir 

 J. W. Dawson f, and Professor J. E. Todd J as holding that 

 a solid earth will alter its shape if the rate of rotation vary. 

 The views of Mr. Peirce I have not seen, but the other two 

 writers mentioned regard the solid earth itself as changing 

 shape only by means of a succession of what we may term 

 catastrophes. Their views seem identical with those which 

 Mr. Blytt's translator ascribes to him in the following words : 

 - — " The sea adjusts itself in accordance with the smallest 

 change in the length of the day .... But the solid earth 

 offers resistance to change of form, and begins to give way 

 only when the tension reaches a certain amount'"' (p. 418). 

 Mr. Blytt makes several distinct references to the subject, 

 and his remarks are not perhaps always strictly consistent. 

 This, however, is hardly to be wondered at since he gives as 

 the result of his investigations : — " As has been stated, there 

 prevails ... a disagreement as to how far the earth will 

 change its form, in case the centrifugal force varies. Thomson 

 is most inclined to believe that it will not ; Darwin is of 

 opinion that it will. And among other physicists whom 

 I have consulted a similar divergence prevails upon this point. 

 One thinks that a lengthening of the day even by several 

 hours will be incapable of altering the form of the solid 

 earth; another believes that the solid earth will probably 

 change its form just as easily as the sea" (p. 421). 



If Mr. Blytt should ever have further occasion to consult 

 physicists on this or any allied point, he would find an exact 

 definition of such terms as solid a certain amount of protection 

 from a priori speculations. Mr. Blytf s own principal view 

 seems due in part to an erroneous interpretation of Tresca's 

 experiments on the flow of metals under pressure. They do 

 not in reality justify his statement " By reason of the 

 enormous pressure which prevails in the interior of the earth, 

 it must be supposed that masses from a certain depth are 

 more or less in a plastic state 3} (p. 417) . It was in fact pointed 

 out some years ago by the Rev. Osmond Fisher § that the 

 existence of an orifice from which the metal can flow con- 

 stitutes a complete difference between the conditions of 



* Proc. Amer. Acad. Arts and Science, vol. viii. 1873, p. 106. 



+ ' Story of the Earth and Man/ ninth edition, pp. 291, 292. 



X American Naturalist, vol. xvii. 1883, pp. 15-26, specially pp. 18, 19. 



§ ' Physics of the Earth's Crust/ ]st edition, 1881, footnote p. 120. 



