621 



rigorous recomputation has been kindly instituted by Colonel Waugh 

 in the latter case ; and as no mistake is found therein, the synopsis B 

 (p. 53) will need no alteration on that account. 



I have now to advert to another subject, also relating to the work 

 in question. In trigonometrical operations, I need hardly mention 

 that the absolute lengths of all linear quantities depend on those of 

 the measured bases reduced to their equivalents at the level of the 



T> 7 



sea, the reduction on which account may be expressed by -, where 



H 



B is the measured base, h its mean height above the sea, and R the 

 radius of curvature : now as we do not know a priori the value of h, 

 unless the measurements be actually made on the sea- shore, the only 

 mode of commencing the work of computation is to assume the 

 nearest value we are in possession of, and when the operations are 

 connected with the sea- coasts, to apply a correction for any excess 

 or defect of our assumption. 



Damargida, the southernmost point included in my book of 1847, 

 is an inland station, the height of which is given in the general 

 report of my predecessor, Colonel Lambton, at 2026 feet ; and as all 

 the triangulation to the south of that station had been concluded in 

 1815, nearly four years before I joined the department, I had no 

 choice but to refer to that as one of my established data : my com- 

 putations start from the Sironj base, and on reaching Damargida it 

 appeared that the assumed value of A, which I had used in correct- 

 ing that base line, was 24*5 feet in excess of what it ought to have 

 been, for which the correction is applied of 2*578 feet to the linear 

 value of the terrestrial arc in synopsis B, and 2'295 in synopsis A. 



Colonel Lambton' s operations, from which the height of Da- 

 margida station is determined, abut on the sea-coast at three dif- 

 ferent points, viz. Madras on the east coast, Mangalore on the west 

 coast, and Cape Comorin on the southernmost extremity of the 

 Peninsula, and the results thence derived were at that time the 

 most trustworthy data I had access to. 



Subsequent to the completion of my computations, the western 

 longitudinal series which connects Damargida with the sea-coast 

 near Bombay, was finished by Captain Jacob, then one of my as- 

 sistants, and there is a note on that subject at page clxxi. of my 

 book of 1847, which is, I presume, quite sufficient to prepare any 



