I 



the Indian Meridian. 403 



wrong*. He also applies a third test, viz. a comparison of 

 the computed and observed azimuth of Kalianpur and Karachi. 

 But the same objection applies to this also. His process goes 

 whoUy upon the untenable hypothesis, that every meridian is an 

 ellipse and the same ellipse, and that every arc of longitude is 

 circular. 



5. There are other indications that Mr. Tennant has taken a 

 wrong view of the subject. For example (paragraph 13), " The 

 attraction is so enormous, if Mr. Pratt's values hold good near 



the mountains " But I particularly specify, and the 



whole line of reasoning shows, that my calculation is not made 

 for such places (see p. 66, note, of my paper). And in the con- 

 tinuation of the note in the next three pages, I point out a me- 

 thod for places in and near the mountains ; so that the wish 

 expressed by Mr. Tennant in paragraph 17 was met in the paper 

 before him, viz. " If an estimate of the attraction at Benog [in 

 the mountains] could be made . . . . " Then in Mr. Tennant's 

 second paper, there are other expressions which show that he 

 has mistaken the matter. He says, " Mr. Pratt has failed in 

 satisfying the geodesical data of the great longitudinal series." 

 But I did not make the attempt. Mr. Tennant must mean that, 

 on applying my calculation to the great longitudinal series, he 

 failed to show that the results tally, on the supposition that the 

 earth's figure is a perfect spheroid. This is what I should have 

 expected, and quite confirms my general view. He says, further 

 on, " It [the ellipticity I deduce for the great arc of 800 miles 

 long] is useless for geodesical purposes." Of course it is, if the 

 geodesical operations are carried on with an assumed, and most 

 probably wrong, ellipticity. If the mean ellipticity be not the 

 right one for that arc, then not that ellipticity, but some other, 

 ought to be used in computing the latitudes of places in the 

 neighbourhood of the arc, otherwise the geodesical operations of 

 the Great Survey will be " useless " for the purpose of attaining 

 to that accuracy which it is supposed to be capable of ensuring. 

 I have read through both Mr. Tennant's papers and his interest- 

 ing calculations with great care. They cannot disprove the 

 results of my paper, for the reason I have stated. The only 

 method will be to point out where my calculations are wrong, 

 or to discover some other cause which, on calculation, is found to 

 nullify mountain-attraction. 



6. There is one of Mr. Tennant's calculations which 1 will 

 make use of to illustrate this subject more at length. 



Let O be the ocean, I' C B A H a vertical section of Hindostan 

 from Punna; on the Great Arc (close to Cape Comorin), through 



* It is worth observing that, in the first of these cases, Mr. Tennant 

 docs pronounce mine to ))e more correct than the mean. 



2 D 2 



