( 107 ) 
the whole. Near one End of this Plank is placed an 
upright fourfided Box, III, Fig, i. and 5. about two 
Feet high, narrower at the Back next the End of the 
Plank than before : Its two Sides are mortifed both in- 
to the Plank below, a a, Fig,^, and into the Top of 
the Box above, dd'^ the back and fore Part are faften’d 
to the Edges of the Sides with Wood-Screws. The 
Top has a circular Hole cut in it, fomething above 
three Inches in Diameter, whofe Centre is about three 
Inches diftant from the outhde of the Back, and at an 
equal Diftance from the two Sides. This Hole gives 
PafTage to a turhing Pillar B, in the Bottom of which 
there is fix’d an Iron Pivot to turn* in a thick Brafs 
Plate lodged in the Plank, b. The upper End of the 
Pillar rifes about an Inch and an half above the Top of 
the Box, and is mortifed into a ftrong Head, K, Fig, i.. 
and 3. about eight Inches in Length, and four or five in 
Breadth and Thicknefs. This Head carries two Cheeks, 
L L, about thirteen or fourteen Inches in Height, their 
hinder Edges, towards the lower End, extending five In- 
ches beyond the Axis of the Pillar backward. ufVlong 
the Back of thefe Cheeks, at equal Diftances above one 
another, there are Notches, tending obliquely down- • 
wards, and anfwering one another in each Cheek, to > 
receive the Pivots of a crooked Iron Axis, C, Fig. 3. 
on which the Tube is plac’d. The Notches are made 
at different Heights, to keep the Eye-Glafs at a proper ' 
Height for the Eye, in different Elevations of theOb- 
jed above the Horizon. The Figure of the Axis an- • 
fwers that of the three under Sides of the Tube. The 
of the Tube lies about two Inches and an half 
higher than the Axis of the Motion upon thefe Pivots, 
and the Centre of Gravity, when the Cbjed-Metal is in, 
is about three Inches backwarjer. To keep the Tube 
from flipping back, when its fore End is raifed, it has 
