152 MEASUREMENT OF AN ARC ON THE 



Note, the quantity +,0074 inches is the expan- 

 sion of the chain due to 1 » of the thermometer as 

 determined hy my own experiments detailed in the 

 annexed memoir. By General Roy's experiments 

 with the pyrometer, it was +,00763 inches. 



The quantity +,01237 inches is the expansion 

 of 100 feet of brass due to 1 ° of the thermometer. 



By the experiments I made in the Mysore the 

 expansion of the old chain was +,00725 inches 

 due to 1*^. By these experiments it is +,00737 

 inches, but I give the preference to the latter on 

 account of the chains being fixed to the wall. 



The radius of curvature for reducing the base 

 to the level of the sea, is assumed at 3448748 

 fathoms being the radius to the meridional circle 

 on which one degree is computed to be 60191 m 

 the latitude of 13''. • - 



Section II. — Observations for determining the 

 Angle which the Base Line makes with the Me- 

 ridian. 



At the North end of the base 



latitude 13° 00 29", 59 N, 



September QAthj on the evening 



the polar star when at its 



greatest Eastern elongation 



was observed to make an an- 

 gle North Easterly with the 



baseline produced, ..... 1° 35' 08", 7 

 The apparent polar distance of 



the star at that time was 1 ° 



44' 40" 2 with which and the 



above latitude, the computed 



azimuth was, 1 47 25 , 7 



