508 ACCOUxVT OF TRIGONOMETRICAL 



be parallel to the chain, and very near it. A piece of 

 wood was contrived to he placed upon the brass head, 

 and fixed by a screw, which pressed against the end 

 of the slider, so that when that shder was moved by 

 its own screw, tlie wood, thus attaclied, moved with 

 it, in tlie direction of the alignement, as nearly as the 

 eve coidd judge. On tlie top of this wood was placed 

 aT^ having also a motion in the same direction with 

 the brass slider, to expedite the o])eration; and on 

 the top of this T, a brass ruler, in length ahont six 

 inches, was placed, having a sliding motion at right 

 angles to the other; and in the middle of the pro- 

 jecting end, was a mark from which the plummet 

 was suspended, and by the two motions, at right 

 angles to each other, the plumb line was easily brought 

 to coincide with the arrow terminating the hypothe- 

 neuse. A like operation was gone through with the 

 commencement of the next hypothenuse, and the 

 arrow brought to coincide with the same plumb line. 

 Here the distance of each arrow above or below the 

 brass rule was noticed as in the former measurement. 



If, after the removal of the transit, the same hypo- 

 thenuse Avas continued, the register picket, at the end 

 of the chain, was left standing; and when the instru- 

 ment was brought into the alignement with the 

 plummet over the mark, nothing was required but to 

 place the telescope at the former elevation or depres- 

 sion, and move the cross vane which is applied to 

 the heads of the pickets and stands, till the appro- 

 priate mark coincided with the horizontal wire in 

 the focus of the eye glass. 



