6 Rev. 0. Fisher on Variations of Gravity arid their 



The formula for the time of vibration of a pendulum, 



t=7r \f ~-, enables us to connect N and Gr ; and it is shown 



at p. [123] that, "as regards reduction for height of station, 



the formula 8N=-JN-p- is sufficiently exact;" N being in it 



taken as 86400. 



Hence it appears that, taking SN as one vibration, the 

 change in G corresponding to one vibration is 



-JL^Gx 0-000023148, 

 = sG (suppose). 



The reduction of gravity for the height of the station may 



2h 

 be taken as g — , because the part of the reduction for height 

 c 



which would depend upon latitude is inappreciable. 



Hence the correction for the reduction of gravity to the 

 sea-level at Punnse for 48 feet is 



Gx 0-0000045875. 

 And the correction to be added to the vibration- number, by 

 the formula for SN, will be 



0-19818. 

 The observed vibration-number at Punnse being 85982*75, 

 we may say that at the sea-level at Punnse, 



N = 85982-95. 



As an instance of the mode of making such a comparison as 

 is proposed, let us take the case of More, the most northern 

 station visited *, being also the most elevated (15,408 feet). 

 More is about 150 miles, by the map f, distant from the sub- 

 Himalayan plains to the south-west of it, and about the same 

 distance N. by E. from Simla. 



Then we shall have : Gravity at* More— gravity at Punnse 

 = difference for difference of latitude, 

 — difference for height, 

 + difference for local attraction. 

 Now the difference for difference of latitude 



=^(l + J 3-6-|m)(fm-6)(icos %'—\ cos2/)J. 

 =g@H cos 2V —\ cos 21), suppose, 



* This was the last station visited by Captain Basevi, who there died, 

 a martyr to his work. See 'Account &c.' p. x. 



t Plate to u Account &c." E 



t Pratt's ' Figure of the Earth/ 4th ed. art. 122, where his - 2 corre- 

 sponds to our g. a 



