By Pror, EMERSON ReYNOLDs, M.D. 
“I 
9 100 89 
2 Mosyuupl? 4 
4 Nex é B 2% 

















the milled head m. As the observing telescope moves over the 
graduated arc g, the index A moves in front of the graduated 
plate B, but in the opposite direction, for the motion of D, is 
communicated to the rod r by means of the serrated slip c. 
When the fittings are well made, the movement of the index A, 
is steady and corresponds in both directions with those of D. By 
the simple means described, a very slight motion of the observing 
telescope produces a comparatively considerable displacement of 
the index A. ) 
In my instrument, the telescope and the index move in opposite 
directions. Any objection on this score can be removed, for it 
is only necessary to point out that the motions may be made 
to coincide in direction by placing ¢ under instead of over the 
toothed wheel. 
Graduation of the glass plate—It is very desirable that the 
graduations on the plate and on the arc of the instrument should 
agree; the best mode of securing this is to graduate the plate 
