272 The Proposed Pendulum Operations for India. [No. 4,. 



The Indian operations will eventually be combined with those taken 

 previously with similar instruments in other parts of the world, to 

 deduce the ellipticity of the earth's mean figure. Both Sir John 

 Herschel and Professor Stokes have remarked, in their letters on the 

 proposed Indian operations, that almost all observations hitherto made 

 have been taken at stations either on islands or coasts, so that a series 

 along the centre of a continent is very much needed. A complete set 

 of observations has been already taken at the Kew observatory by 

 Mr. B. Loewy, with the Indian apparatus ; and on the completion of 

 the experiments in this country it will be returned to Kew, in order 

 that final observations may be taken, to show whether the pendulums 

 have undergone any change hi the interim. 



It is to be hoped, however, that so good an opportunity will not be 

 lost cf extending these observations to stations easily accessible from 

 India, though not included within its limits. On this head Professor 

 Miller's opinion may be emoted at length, " Much would be added to 

 the value of the observations made at the stations of the Indian 

 survey, if, before the pendulums were brought back to England, 

 observations could be made with them at some other points, especially 

 points nearer to the equator, such, for instance, as the south coast of 

 Ceylon, Singapore, or on the coast of Borneo. Another accessible 

 point, interesting from being in a long line of depression, where a 

 large gravitation might be expected, is Aden." 



The intention of the Russian government, to have similar obser- 

 vations made along the Russian arc, has already been alluded to- 

 If, after the return of the pendulums to England, they were to be 

 swung at one of the Russian stations, it will be possible to combine 

 the Russian with the Indian operations, and deduce a value of the 

 earth's ellipticity from exclusively Continental observations, extending 

 from Cape Comorin to the northernmost part of Finmark. 



" turbances of the other kind. Indeed it is theoretically possible, from the ver- 

 " tical disturbances, supposed to be known, actually to calculate the horizontal 

 " disturbances, and that without assuming anything 'beyond the law of universal 

 "gravitation. Actually to carry this out, would probably require observations 

 " to be made at stations more numerous than can be thought of, but the fact of 

 " its possibility shows how severe a check pendulum observations are capable of 

 " exercising on the results of geodetic observations." 



