212 The Great Indian Arc of Meridian, [No. 3. 



in some other manner, and then determine the other by the com- 

 parison of the amplitudes. I can conceive of no means of finding 

 the curvature of the arc by any independent method: but the 

 other error, the effect of attraction, can be determined by direct 

 calculation, though at first sight a hopeless and in the end a very 

 laborious operation in the case of such a huge and irregular mass 

 as the Himalaya mountains, and not practicable without some such 

 expedient as that which I have called the "Law of Dissection" in 

 the paper in the Philosophical Transactions. 



12. The main results of the calculation of attraction in that 

 paper are as follows : — 



Deflexion of plumb-line in meridian at Kaliana = 27",853. 

 Ditto at Kalianpur = 11".968. 



Ditto at Damargida = 6".909. 



By means of the property of a curve I find the law of meridional 

 deflexion for all stations on this double arc (but for no other places) 

 to be 



„ .-,. , -r. „ • 114".712 



Meridional Deflexion = -= — 7 , - „ ^ 

 L — I -f- 3.520 



I and L being the latitude, in degrees and parts of a degree, of 



the proposed station and of Kaliana, the north extremity of the 



arc. It is the application of these corrections to the astronomical 



observations, and then the comparison of this corrected astronomical 



amplitude with the computed amplitude (as described towards the 



close of para. 11) which brings out the corrected ellipticity z -|-g- for 



this arc, instead of 3^^. 



13. Mr. Airy in a paper in the Philosophical Transactions for 

 1855, (p. 101,) states that he was at first very much surprised at the 

 large amount of the deflexion thus discovered. And he goes on to 

 suggest a remedy. But he does not call in question the correctness 

 of my result. He throws out the idea, that there is another cause 

 in operation which counteracts the effect of the attraction ; viz. a 

 deficiency of attracting matter immediately beneath the mountain 

 mass. Three objections were started to this hypothesis in the 

 postscript to my second paper (on the English Arc), p. 51 of the 

 Transactions for 1856. They are more fully discussed in the Philo- 

 sophical Magazine for November 1855. No answer has been given 



