of an Arc of the Meridian. 403 
carries a Y, hidden in this elevation, by the upper part of the 
head of the microscope. 
In the middle of the cross pieces, which unite the side of the 
frame to its corresponding one, are two wheels with long axles, 
as before mentioned. In this elevation they are seen at B and E ; 
and have strings passing from them to their respective sides of 
the tube, where they attach to the pins P, P. At the ends of the 
axles nearest to this elevated side are two other pulleys. In the 
view which this plate affords, these wheels are projected against 
the others just spoken of ; but their uses will be more readily 
understood, on perceiving the strings which pass over the upper 
pulleys, and afterwards sustain the weights W, W, in their up- 
right cases. 
In this elevation is seen the telescope attached to the side of 
the great tube : it is used when the instrument is got into the 
plane of the meridian. The vessel for receiving the plummet is 
seen at V; and at S the adjusting-screw, for elevating or depressing 
the frame which supports it. LL is the clamp-arch, supposed 
to be attached to the other side of the tube, or that which sup- 
ports the lamp. At the bottom of the stand is seen the azimuth 
circle, and the apparatus belonging to it. 
For the purpose of conveying a clear idea of the arrange- 
ment of the lower pulleys, and the manner in which the two 
arches are joined to each other at the end of the telescope, there 
is given, in Plate XII. a horizontal view of the same. The vessel 
for receiving the plummet, its supporting frame,and the magnifier 
for viewing the dots or points on the divided limb, are likewise 
represented. The body of the telescope is here taken away, 
leaving nothing more than the plate at its end, with the conti- 
guous work belonging to the wires.. 
