﻿324 Oy EXTENDING A GEOGRAPHICAL SURVEl* 



hard well-seasoned wood, in a manner so simple as to 

 render a description unnecessary. 



I FouxD, however, in the course of practice, that 

 tripods, with elevating screws in the centre, answered 

 much hetter than the pickets for the intermediate 

 ends of the coffers, particularly as a very great part 

 of the ground was hard and stony. Those tripods 

 are described by Gexeral Roy. Those which I 

 used, as I had not the means of getting better, were 

 no more than the common wooden press screw, made 

 to move up and down by a female screw with handles ; 

 the top of the tripod being a thick piece of wood 

 for the screw to pass through, with another piece of 

 wood three or four inches below that to keep it 

 steady — but a boxed tube to receive the screw is to 

 be preferred. 



BONING TELESCOPE. 



For the purpose of fixing the objects in alligne- 

 ment, 1 used the circular transit instrument, which 

 answers remarkably well, both for that purpose and 

 for laying off the principal elevations and depres- 

 sions of the different hypothenuses ; but when the 

 pickets are to be placed so that the coffers may be 

 laid in the line of the hypothenuse, I made use of 

 one.of ?vlr. Ramsdex's spirit levels ; but in place of 

 using its three legs, I took them off and placed the 

 telescope, with its adjusting screws, upon a tripod, 

 liavino- an elevating screw in the centre, passing- 

 through a tube with a small iron screw to keep it 

 lirm. On the top of this elevating screw was fixed 

 a piece of board about ten inclies square — upon that 

 again Mas placed another piece, which v/as made to 

 move in a groove by a finger screw, and upon this 

 moveable piece the levelling telescope, with its ap- 

 paratus, was fixed, having its axis at right angles to 

 the direction of the groove, so that by the finger 

 screw it could easily be moved to the right or left, 

 and brought into the direction of the allignement. 



A SMALL 



