﻿ACROSS THE PENINSULA OF INDIA. 325 



A SMALL square picket, or boning rod, with a 

 piece ten inches in length, fixed at right angles, and 

 made to slide up and down, and fasten by a small 

 screw, was placed at the further extremity of the 

 hypothenuse, and the sliding piece put at a conve- 

 nient height : that piece therefore mari<ed the angle 

 of elevation or depression. The height of the axis 

 of the transit circle, (when that instrument was used,) 

 having been taken by a plumb line, as well as the 

 point (iireClly under its centre : Then having marked 

 out one hundred feet, by a common measure, exadly 

 in the allignement, 1 removed the transit, and placed 

 the tripod, with its apparatus, precisely on the spot 

 which marked its centre ; and measured its height 

 above that spot, comparing the centre, on which the 

 levelling telescope moves, with the transverse axis of 

 the transit, (having previously determined the most 

 convenient height for the coifers to be from the 

 ground.) Then I took the exad; measure of the 

 space between the axis of the transit and that of the 

 levelling telescope, and applied it to the boning rod at 

 the extremity of the hypothenuse, and made a mark, 

 at that distance, below the cross slider. 



The level was then adjusted by the screws and 

 spirit level, and its centre brought into the alligne- 

 ment ; which being done, the axis of the telescope 

 was elevated, or depressed, until the cross wire cor- 

 responded with the mark en the boning rod. 



If the angle of the hypothenuse be beyond the 

 limits of the vertical screw of the level, the tripod 

 must incline so as to bring it within'those limits, and 

 that angle of inclination noticed, that the perpendi- 

 cular height may be justly determined ; that however 

 never happened. 



But, as the angles of elevation and depression 

 were in general very small, 1 contrived to take them 

 with a small sextant, both on account of saving time, 

 and to avoid running unnecessary risk with the cir- 



Y 3 . cular 



