310 MEASURE OF A DEGREE ON THE COROMANDEL COASTV 



scale I originally proposed, and what is here offered is the 

 beginning of that work, being the measurement of an arc 

 on the meridian, from which is deduced the length of a de- 

 gree for the latitude 12° 32', which is nearly the middle of 

 the arc 



An account of the base Tine. 



The place of Some time had been taken up in examining the country 

 best suited for this measurement, and at length a tract was 

 found near St. Thomas's Mount, extremely well adapted for 

 the purpose, being an entire flat, without any impediment 

 for near eight miles, commencing at the race ground, and 

 extending southerly. This being determined on, and the 

 necessary preparations made, it was begun on the 10th of 

 April, and completed on the 22d of May, 1902. 



Instruments I had expected a small transit instrument from England, 

 ' for the purpose of fixing objects in the alignement, and for 



taking elevations and depressions at th£ same time ; but that 

 instrument not having arrived, I thought it unnecessary to 

 wait, particularly as the ground was so free from ascents and 

 descents ; I therefore used the same apparatus as I had for- 

 merly done, viz. the transit circular instrument, and the le- 

 velling telescope fixed on a tripod with an elevating screw 

 in the centre. In all horizontal directions, this telescope 

 fully answers the purpose, and as there has been no deviation 

 from the level to exceed 26' 30' , excepting in one single 

 chain, and those cases but very few, I feel entirely satisfied 

 as to the accuracy of the whole measurement. 



The chain. The chain which was made use of is the one 1 formerly 



bad ; and I was fortunate enough to receive another from- 

 England, made also by the late Mr. Ramsden, and this 

 having been measured off by the standard in London, when 

 the temperature was 50° by Fahrenheit's thermometer, it 

 afforded me an advantage of correcting for the effects of 

 expansion, a circumstance in which I was by no means sa- 

 tisfied in the former measurement. In order, therefore, to 

 have a standard at all times to refer to, I hiive reserved the 

 new chain for this purpose, and used the old one only as a 

 measuring chain, by which means I can always determine the 

 correction for the wear. 



There 



