MEASURE OF A DEGREE ON THE COROMANDEL COASt. AC 



rour was repeatedly examined and found to be 2"*36 to be 

 substracted from the elevations and added to the depressions 

 when the telescope is in the ordinary position, or when the 

 semicircle and microscope are on the left hand ; but vice 

 versa whtia in the contrary position. These errours of the 

 semicircle and line of collimatiou being opposite, the result 

 from comparison will be, " That when elevations or depres* 

 sions are taken with the semicircle, l' 26" must be added to 

 the former, and substracted from the latfer^ 



And that when the elevations and depressions are taken 

 by the micrometer in the eye piece 2"*36 must be deducted 

 from the elevations and added to the depressions. 



The micrometer in the focus of the eye-glass of the tran- Micrometer, 

 sit telescope is the same in all respects as the one mentioned 

 by General Roy, that is to say, the circle or scale is divided 

 into one hundred divisions, and there is a nonius fixed to 

 the upper part of the telescope, which defines the revolu- ^ 



tions of the micrometer as far as ten for the elevations, and 

 ten for the depressions. Several experiments were made 

 with the same marked bamboo, for ascertaining the value of 

 these divisions, and it was found, that seven revolutions an4 

 6 1*4 divisions were equal to ten minutes on the Umb of the 

 semicircle, so that one division was equal to -yss of a se- 

 cond. 



Having given tables of all the angles, Major Lambton 

 adds. The angles have been taken with much care, and I Remjrks an 

 believe with as much accuracy as the nature of such a pro- ^^ angle* 

 oess admits of; difficulty, however, very frequently ar<?se 

 from the haziness of the weather, which rendered the ob- 

 jects at the very distant points extremely dull, and occa- 

 sioned some irregularity in the angles. Whenever that hap- 

 pened, the observations were often repeated, and in ease aoy 

 one, in particular, was different from the other so much ag 

 ten seconds, it was rejected till tlie three angles of the tri- 

 angle bad been pbserved. If the sum of these angles was 

 near what it ought to be, no further notice wag taken of it; 

 but should the sum of the three angles be nearer the truth 

 by taking it into the account, and that there appeared aq 

 irregularity in the other two observed angles, I Have made 

 p.t a rule to take each observed ajigle as a. correct ope, an4 



dividf 



