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



A table of the resulting elements is given, together with a memoran- 

 dum specifying the mountains which could be identified as having been 

 previously observed by other surveyors. J. T. W. 



Of the Secondary Mountain Triangulation. 



57. The magnitude of the triangles for determining the. positions 

 of the hill peaks, and other unavoidable peculiarities attendant on 

 the operations in general, have necessitated some few departures from 

 ordinary precedents in the performance of the required calculations. 

 These may be briefly noticed. 



58. Identification. — The primary difficulty which the computer 

 meets with is, in the identification of the numerous points whose 

 positions have been determined. Observed by different persons, after 

 long intervals or from different points of view under the disadvan- 

 tages of altered aspects, the same hill will be found noted in the 

 angle books under various characteristics. For instance, Mont 

 Everest was called v by Colonel Waugh, n by Mr. Nicolson and o by 

 Mr. Armstrong, while the peak XXXVIII. is named n 2 at one sta» 

 tion of observation, ?i 3 at another and " I west peak" at a third, by 

 the same observer. This plurality of characteristics, under the 

 circumstances, is clearly unavoidable. It remains to state how the 

 required identification was effected. The principal series was first 

 carefully projected on a scale of 4 miles to the inch, and the several 

 rays emanating from stations of observation were next exactly drawn. 

 The intersection of these rays, assisted by the characteristics forth- 

 coming in the angle books, more or less distinctly defined the points 

 sought for. This was treated as an approximate identification, 

 whereby the bases required from the principal series and experimental 

 triangles to be computed became known. The former were then 

 obtained in the ordinary way, by means of the contained angle and 

 logfeet of the including sides, for which computation the following 

 well known formula was found useful, 



C 

 tan J (A — B) = tan (45 — Q) Cot — 



2 



h 



wherein tan Q = — 



