Description of the Solar Index. 309 
and make this adjustment very accurately. During the process 
it will be important to keep the hair well stretched. 
The manufacturer should take care to have the plane of the 
face of the quadrant parallel to the central line of the cylindrical 
portion of the equatorial axis. If the central line of the pivot 
should not meet with the central line of the cylindrical portion of 
this axis, the preceding adjustment will remove ¢hat source of error. 
The central line of the horizontal axis B should be parallel 
with the base A of the instrument; and a fine line should be 
drawn upon the top of each of the apnahts C and D, in direction 
of the axis and directly over its central section. Also a fine line 
should be drawn at right angles to the face B, over the centre of 
the hole near Q, which receives the equatorial axis; as likewise 
across the hole at the extremity R of the tube. By means of 
these it will be easy to know if the tube is at right angles to the 
axis, and if not to bring it into this position. 
Let the base A be put upon the base of the compass on the 
side of the box opposite the spirit levels, or, if the compass has a 
vernier on the side opposite the levels, remove the levels and 
place the base there, confining it by its appropriate screw. Re- 
moving the glass from the compass, fix it at a convenient height 
with the plane of its horizon perpendicular with the horizon of 
the place, so that facing it and suspending the plumb X by its hair 
directly in front of it and as little distant as practicable, the hair 
when still sha!l appear at one view to pass over the east and west 
points of division; then if the plumb be brought before the ends 
of the uprights C and D, and the hair appear at one view to pass 
exactly over the fine lines drawn upon them, the base A will be 
in its right position. But if both of these do not disappear at 
one view behind the hair, alter the position of A, and proceed as 
before, till the right adjustment of the base shall be effected ; the 
horizontal axis B will then be parallel with the line joining the 
east and west points on the horizon of the compass. Let a mark 
be made on the base of the compass corresponding with one made 
on the edge of A. By means of these alone the base A can 
ever after be placed and fixed in its proper position; and there 
will be no further occasion for removing the glass to accomplish it. 
Framingham, Mass., July 12, 1845. 
Vol. xt1x, No. 2.—July-Sept. 1845. 40 
