j -8 Gen. Roy’s Account of 
pended from the center of the inftrument above, is accurately 
brought to co-incide with the point marking the ftation under- 
neath. The third or uppermoft plane of mahogany is in fa<ft a 
part of the inftrument itfelf, being at all times by fcrews or 
otherwife united to it, and carrying the handles whereby it is 
lifted out for ufe, or in again into its cafe, to be tranfported 
from place to place. In the middle of this plane or bottom to 
the inftrument, there is another conical brafs focket, of three 
inches and a quarter in diameter, fitted to flip over and turn 
eafily on that in the center of the odtagon underneath. In the 
brafs cover of this focket, there is a very fmall hole concentric 
with the inftrument, to fuffer the thread or wire to pafs, which 
fufpends the plummet ; and in the view, Plate III. may be 
feen another fmall box that contains the thread, with a winch- 
handle for railing or lowering the plummet, according as the 
height of the inftrument above the ftation on the ground, or 
edifice where it ftands, may require. 
Art. IV. Feet Screws for levelling the infrument. 
By attending to the group reprefenting the front elevation of 
the feet fcrews, with its fide nuts, in the right hand upward 
angle of Plate V. it will appear, that they are blackened, which 
is always the cafe before the inftrument is levelled, to give 
room for that operation by the adtion of the fcrews. This 
being done, the fide nuts are brought to prefs gently on the 
horizontal plate that embraces the whole group, and thereby 
keeps the inftrument as it were united to the mahogany until 
feme freih adjuftment becomes neceffary. When the inftru- 
ment is to be put into its cafe, then the feet are let down, and 
by the fide nuts the horizontal plate is brought to prefs ftrongly 
on 
