344 Dr. E. B. Rosa on the Specific Inductive 



would be fully supported, so that its altitude above the mean 

 ocean-level would correspond exactly with its thickness. The 

 subject has been fully discussed by Prof. R. S. Woodward, of 

 the U.S.A. Geological Survey, and he has calculated the 

 amount of submergence at varying distances from the edge 

 of the ice for various dimensions of the ice-sheet*. He 

 gives a table showing the disturbance of the sea-level attri- 

 butable to an ice-cap of 38° angular radius and 10,000 feet 

 uniform thickness, and of the variation of the sea-level 

 attributable to the same mass, on the supposition that the 

 north and south poles have been alternately glaciated, as Dr. 

 Croll's theory would require them to be. It appears from his 

 figures that a submergence of about 1000 feet would be pro- 

 duced at the margin of the ice-cap under those circumstances. 

 It will be observed that the thickness of the ice assumed is 

 extremely great, and that this cause of submergence is not 

 nearly so effective for a given thickness of the ice as that of 

 subsidence, which we have just considered. At the same 

 time it is certain that such an ice-cap, if so supported, would 

 produce the effect described, although it is by no means 

 certain that it would be supported. 



It may be asked whether these two theories of submergence 

 are necessarily alternative. Why may not the submergence 

 be partly due to subsidence, and partly to the attraction of 

 the ice-sheet? The answer seems to be, that these two causes 

 of submergence cannot exist together, because, if the crust 

 were to be depressed into the substratum a mass of heavy 

 magma beneath, approximately equal to that of the ice, would 

 be displaced, and distributed through the general spherical 

 interior. There would therefore be no increase of mass in the 

 immediate region of the ice-sheet to disturb the mean level of 

 the ocean. 



XXXIX. Further Experiments on the Specific Inductive 

 Capacity of Electrolytes. By Edward B. Rosa, Ph.D., 



Professor in Wesley an University*. 

 [Plate IX.] 



I. TN a note appended to an article on the " Specific Induc- 

 JL tive Capacity of Electrolytes/'' in the Philosophical 

 Magazine for March 1891, I referred briefly to some experi- 

 ments then under way on the behaviour of glass in a non- 



* " On the Form and Position of the Sea-level," Bulletin of the United 

 States Geological Survey, No. 48. Washington, 1888. 

 f Communicated by the Author. 



