28 



OLDHAM: THE STRUCTURE OF THE HIMALAYAS, ETC. 



distance of 40 to 50 miles the further increase is very small, and 

 may be ignored. The effect of the compensation on the other 

 hand increases and the net effect, after reaching a maximum, goes 

 on diminishing with an increase in the dimensions of the plateau. 



Table 3.-- Attraction of a circular plateau, of varying radius and 

 elevation, at a point centrally situated on its upper surface, due to 

 the visible topography, and to the same, compensated in accord- 

 ance with the Hayjord and Bowie tables. All values positive 

 and expressed in dynes. 





» 1,000 ft. 



5,000 ft . 



10,000 ft. 



15,000 ft. 



Radios in 











1 





miles. 











I 









top. 



com p. 



top. 

 •118 



comp. 

 •114 



top. romp. 



1 



top. 

 •190 



com]). 



1-4 



•031 



•031 



•172 104 



•185 



2-2 



•031 



■031 



•135 -129 



•215 -203 



•260 



•244 



3-2 



•031 



■031 



•140 1157 



•250 



•234 



•321 



•297 



5-2 



•031 



■031 



•154 



■111 



•282 



•268 



•383 



■345 



7-8 



•031 



•030 



•159 



•/.'/ 



•301 



-266 



•422 



•307 



11-7 



•031 



•028 



•163 



•137 



•318 



•204 



•452 



•373 



17-9 



•031 



•025 



•105 



•127 



•325 



•249 



•473 



•359 



36*8 



•031 



•020 



•1(58 



•101 



•336 



•202 



•494 



•295 



(il-l 



•031 -018 



•170 



•075 



•338 



■155 



•502 



•220 



103*3 



•031 -009 



1 



•170 

 1 



•050 



•341 



1 



•108 



•508 



•159 



From the figures in Table 3, it will be seen that in the case of 

 a plateau extending for distances measured by hundreds of miles, 

 it may well be that the effect • of compensation will completely 

 neutralise that of the attraction of the visible mass, and the result- 

 ing attraction of gravity be the same as if the whole of the elevated 

 mass were non-existent. We may also find in these figures an 

 explanation of the fact that the anomalies of gravitation above 

 sea level tend to be positive if the effect of the visible topography 

 is ignored, and negative if it is considered, for in the first case no 

 regard is paid to the increase in the local attraction due to the 

 mass above sea level, and in the second a greater effect is attributed 

 to it than it actually exerts. Further, it is obvious, from a con- 

 sideration of fig. 3, that an increase in the depth of compensation 

 would enlarge the limits within which the effect of the visible mass 

 predominates over that of its compensation, and so increase the 



[ H6 j 



