302 Description of the Solar Index. 
axis, turning in the uprights C and D. The end of this axis 
passing through D, has a screw cut upon it, and receives a nut F 
with two milled heads, which serves to fasten the axis in any 
position by bringing its shoulder firmly against the upright D. 
This nut, where it presses the upright D, should have a less diam- 
eter than this shoulder; that in being tightened it may not turn 
the axis. The other end of this axis is conical; and the upright C 
which receives it, presses hardly upon it, which prevents its be- 
coming loose on wearing. ‘These uprights are fastened to the 
base A, by screws underneath. HE, is a tube screwing into one 
end of the horizontal axis B, and receiving the equatorial axis 
PQR, to which, on the part PQ, a small quadrant GHI is at- 
tached. This equatorial axis passes at right angles through the 
horizontal axis into the tube E, where it turns smoothly, admit- 
ting an equatorial motion to the bar K. The lower extremity of 
this tube is boxed with block tin, and the equatorial axis passes 
into it with a slight taper; thus affording the means of receiving 
the requisite degree of tightness to sustain the quadrant and its 
attaches in any position, while its own motion is sufficiently free. 
The cylindrical portion of this axis is about ;1; part of an inch 
longer than the tube will receive; that, on wearing, it may grad- 
ually sink into the tube and move there without play. A pivot 
soldered fast to the back of the bar K, in the common point of 
meeting of the medium line of this bar and that of the arm LM, 
passes through the centre of the quadrant and through the equa- 
torial axis; where it turns freely, as the extremity of this arm 
moves along the limb H, and shows the various positions of the 
bar K, with respect to the equatorial axis. This pivot, which is 
slightly tapering towards the back of the instrument, has there a 
screw cut upon it, and receives a nut with a milled head, by 
which the requisite degree of tightness is obtained. ‘This pivot 
is so large as to have the proper degree of tightness when the 
back of the bar K is about 4; part of an inch distant from the 
face of the quadrant; and the arm LM, near its junction with 
the bar K, is slightly bent towards the face of the quadrant, so as 
to give a light pressure to the extremity of it upon the limb of 
the quadrant. 
Attached to the arm LM, is a small spirit level; and it is fur- 
nished at its extremity with a vernier, by means of which it may 
be adjusted to any desirable position upon the limb H of the 
‘ 
ae sl 
