108 
Description of a 
Explanation of the Plate . 
Fig. 1, Plate 3*-— Geometrical elevation of the telegraph* 
seen from behind* with a perpendicular section of the 
chamber of observation. One half of the telegraph and 
frame is seen covered with black cloth, or painted* 
leaving only the windows of the chamber permeable 
to the passage of light. This back part of the telegraph 
chambers* when complete* is equally covered with the 
front. It is left unfinished here to permit the view of 
the different chambers. 
ABC!)* the frame on which the telegraph is raised. 
EF* the semicircular frames of iron or copper* subdivided 
into 13 chambers. 
G* the rods or radii supporting it on the wooden frame. 
H* the shaft passing through the lower beam CD into the 
observatory* and playing in the socket a . 
I* the shoulder attached to the shaft* and fixed firmly in 
the beam* its lower part playing in a circular opening 
of the roof. The ropes &* c* are seen descending from 
one*pf the wheels* through the perforations of the beam 
and shoulder. 
dd * iron castors or rollers sunk into the beam* on which 
the telegraph and frame rotate in horizontal circles on 
the roof. 
K* the iron cap on the top of the shaft* branching out into 
the arms which support the axes of the wheels* the in- 
ner one of which* 
L* is here seen* having a shutter e* morticed firmly into its 
interior surface. The other shutter/* is seen covering* 
on the off side* one of the chambers of the telegraph* 
and is attached to the returning arm of the solid axis. 
This is more clearly seen in fig. 2. 
M* the tower or parallelogram raised above the tele- 
graph $ divided into three chambers* one of which is 
