38 The Trigonometrical Survey of India. [No. 1, 



first instance adopted. The selection has been made to the exclusion 

 of those values obtained from short sides. 



DedUCti ° n ~™ angi }/=-°^7. 

 SS rga " J ]/= "WB8. 



?o°„Tlo DanSi }/= - 07915 - 

 Thak„„,-ga„j | /= 07M9 



Til"' }/ =-00Ml. 



l on ? ]0 .. )/= .08043. 



Darjeehng y 



Mean / = .0744. = T |. T nearly. 



69. With this value of f, the heights from Senchal and Tonglo 

 were computed, and the mean of these values, as also the differences 

 between each value and its mean, were next found. The heights were 

 now corrected, in such wise, that when the heights deduced from 

 Senchal are compared with the mean heights already mentioned, the 

 greatest + and — differences should be numerically equal. The 

 same process being gone through at Tonglo, H. S., there resulted 

 the mean values of f, which have been employed for that station and 

 for Senchal. These values will be found recorded in the heights 

 herein given, and it will also be found, that they have been employed 

 for all heights of the /S^S-Himalayas observed at Senchal and Tonglo 

 hill stations. 



70. It may be useful to remember, that if there be two points 



A and B observed from O, whose heights respectively are 7i a and lij, 



determined by a certain value oi f at O —f - Also if d a equal 



corrected geodotic distance O to A, and db = O B. Then if f vary, 



so that h a (the height of A computed from O) changes by + S a , and 



?> d 2 



hb by i Sj, so will ± — oc -j-. Hence should the foregoing method 

 o a d a 2 



for finding the value of f at plain stations in terms of the observed 



value at hill stations, be hereafter ever adopted, it will be found 



advantageous to construct a table of the squares of the distances in 



miles, for this purpose. 



71. The general principle of procedure is now apparent. But as 



