212 
PROCEEDINGS OF SECTION A. 
axis AA, made of H-shaped steel girder, the section of which is shown 
at A A, No. 11, A A rests at its lower end on a hemispherical steel 
bearing A 1 , and at its upper end on a cylindrical axis T in segmental 
bearings No. 7, from wnich part of the weight is taken by the friction- 
wheel collar UTT, Fig. 8, and the weighted bent lever U, No. 15 ; the 
down thrust at the lower end A 1 being in part taken by friction rollers, 
lever and weight UUU resting against a sleeve end to the wheel NN. 
So far we have a very simple equatorial mounting of great stability, and 
very easily moved, and weighing about two tons ; to this is added the 
graduated K A wheel NN, and the tangent screw wheel N 1 N 1 ; this 
screw wheel works freely on a cylindrical bearing, and adds very little 
to the friction and freedom of movement in the polar axis, at the same 
time it can be instantly clamped to the wheel NN at the point K by 
half a turn of the handle J at the eye-end of the telescope through 
two pairs of bevel wheels at JJ. (See also J, No. 11.) The detail of 
the point K will be seen in Nos. 9 and 10, in u Inch LK is a 12 to 1 lever 
pivoted on the wheel NN — i.e., the BA wheel at K'. In No. 9 part of 
the clamping-rod J is shown ; by means of this the piece K is clamped 
into a T-shaped groove in N', and this sliding piece K is linked to the 
upper end of the lever LK 1 at K“. The lower end of the lever LK 1 is 
shaped as an are of a circle, and on it is a rack worked by a pinion and 
series of wheels at M, and controlled by an endless cord not shown. The 
grooved wheel and other details of this are shown in Diagram No. 3. 
This arrangement was designed to work instead of the usual tangent 
screw for slow motion, and it performs its functions very much better 
than a tangent screw, being quieker and more accurate than a screw. 
The clamp in declination can also be controlled at the eye-end of the 
telescope by the handle II through a pair of bevel wheels at H. (See 
also Diagram No. 11.) The declination clamp surrounds the declina- 
tion axis at G No. 11, and the rod H No. 11 projects into the collar 
G slightly, but it is shaped there as in Diagram No. 12, which makes 
it act as an eccentric, and when it is turned by the handle H it clamps 
the declination collar that works in Q No. 11 — that is, when the upper 
or cut-away part, as in Diagram No. 12, is outward, the collar is not 
clamped, but when it is turned half round the lower or full part is 
brought outwards and projects, thus clamping the declination axis to 
the collar. Slow motion in declination is given by wheels and pinion 
at the end of the clamping collar similar to that shown in No. 3, in 
which one pinion of ten leaves is fixed on the axis of the grooved 
pulley, and this works into the wheel G of 100 teeth, which has a 
pinion working into the curved rack on the end of the lever C. 
Diagram No. 14 shows the clockwork, which is electrically controlled 
every second ; this is in all respects similar to the clock and control of 
the star camera, and for details the reader is referred to the description 
of that instrument in No. 81 of our records. It may suffice here to 
say that the motion is controlled by a standard astronomical clock 
which makes it absolutely correct every second, and limits the possible 
error during any second to part of a second of time. 
On the axis of the telescope Nos. 15 and 11 are two declination 
circles EE, each read by two microscopes FE, FF. Each pair of 
these are placed so that the observer may turn from one to the other 
without changing his place ; the micrometers to be divided to seconds 
of arc and easily read to OT". 
