*59 
the Trigonometrical Operation. 
i 
Art. XXIII. To fet the Rod on which the elevation level hams 
par allel to the line of Collimation. 
The vertical axis being fuppofed to be nearly vertical, hang 
the level on its rod, and redify the bubble by the finger fcrew 
of the clamp. Set the horizontal wire on the fteel Hide to 
interfed the center of the oblique wires, and place the dart or 
index at zero on the micrometer head. Then obferve fome 
diftant diftind objed covered by the horizontal wire. Invert 
the femicircle, that is, turn the azimuth circle i 8 o°, and the 
telefcope upfide down, fo as to bring the wire upon or nearly 
upon the fame objed. Now, if the level be not right, redify 
it by the finger fcrew at the tail of the clamp. If the telefcope 
does not now accurately cover the fame objed as in the former 
pofition, bifed the difference by the finger fcrew of the clamp, 
and then redify the bubble by the capftan-nuts under one end 
of the rod. Repeat this operation until the level is right, 
when the telefcope fees the fame objeds in both pofitions, and 
thereby the rod will be brought parallel in altitude to the line 
of collimation or axis of vifion. 
The adjuftments of the rnicrofcopes having been already fuf- • 
ficiently explained, in giving the defcription of the eflential 
parts of the inftrument, it is unneceffary here to repeat them. 
Art. XXIV. Of the weight of the infirament, and mode of 
tranfporting it from place to place. 
The inftrument, whofe defcription and ufes we have here 
attempted to give in a general way, without reference to its 
minute parts, by a multitude of different charaders, weighed in 
tl.e whole about 200 lbs. It is contained in two deal boxes ; 
one 
