﻿308 



Royal Society :■ 



in becoming solid from a fluid state ; and that below the sea-level, 

 under mountains and plains, there is a deficiency of matter approxi- 

 mately equal in amount to the mass above the sea-level ; and that 

 below ocean-beds there is an excess of matter approximately equal 

 to the deficiency in the ocean when compared with rock ; so that the 

 amount of matter in any vertical column drawn from the surface to 

 a level surface below the crust is now, and ever has been, approxi- 

 mately the same in every part of the earth. 



In order to make this hypothesis the subject of calculation, the 

 author takes the case of the attenuation of matter in the crust below 

 mountains and plains, and the excess of matter below ocean-beds, to 

 be uniform to a depth m times the height above the sea-level or the 

 depth of the ocean, as the case may be. 



The results are shown in the following Table, in which the num- 

 bers are the last figures in the ratio of the differences of gravity to 

 gravity itself, carried to seven places of decimals. The decimal point 

 and ciphers are omitted for convenience. 



Stations. 



Differences of gravity. 



Relative 

 effects of local 



attraction 

 deduced from 



pend ulum- 

 observatio ns. 



Residual errors after correction by the 

 method of 



Dr. Young. 



This hypothesis. 



»n = 50. 



?ra=109. 



Indian-arc stations. 



Punnoe 



+384 

 -323 

 +341 



-707 



+'302 

 -166 

 -197 

 +142 



+894 



-562 

 -926 



-208 

 -957 



+314 



-154 



-192 

 + 153 



+906 



-"•78 

 -455 

 +338 

 + 69 



+331 

 — 122 



-138 

 +216 



+ 31 



-557 



-584 

 +315 

 +320 



+'360 

 . - 79 



- 78 

 +291 



+102 



Bangalore 



Damargida 



Kalianpur 



Kaliana 



Coast stations. 



Punnoe 



Alleppv 



Mangalore 



Madras 



Cocanada 



Ocean station. 



Minico j Island 



The author points out from this Table that Dr. Young's, or tne 

 usual method of correction for local attraction, so far from improving 

 matters, introduces very large residual errors of the arc and ocean 

 stations, and, at places on the arc of meridian, all lying on the same 

 side with reference to Punnoe. He observes that neither the usual 

 method nor his own much affects the coast stations ; and attributes 

 this to the want of more complete knowledge of the contour of the 

 surface, both above and below the sea-level, in these parts. But his 

 own method, in the case m=50, remarkably reduces the effects of 



