154 
THE EARL OF ROSSE ON SOME RECENT IMPROVEMENTS MADE 
The clock has a tram of five arbors, the first, carrying the barrel, being worked 
by a weight of about 30 cwt. (acting through a single pulley) descending half a foot 
per minute. The fifth carries a ball-governor like that usually adopted but with a 
higher velocity, and springs are employed to assist gravity in acting in antagonism 
to centrifugal force. A pulley (A) fixed upon the third axle transmits the motion 
through the medium of an endless rope of galvanised wire to a pulley (D) (Plate 11, 
figs. 1, 2, and 3), fixed at the eastern end of a wrought-iron pipe (G H). A 
weighted lever with a pulley (C) at its extremity serves to keep the wire-rope at 
the requisite degree of tension. The pipe (G H) is supported near its centre of gravity 
from a beam (E E) by a standard (K) with a set of rollers in a five ring, and is pre¬ 
vented from moving endwise towards G by an annular bearing, and towards H by a 
centre bearing. The beam at its eastern end rests, through the intervention of a 
strong piece of “T-iron., provided with rollers, against a circle of about 40 feet radius 
(which remains fixed to the eastern wall as heretofore). The beam runs through a 
socket provided with rollers (R R). The socket is attached to the tube (a portion of 
which, 0 O, P P, is shown) by a pin (M), and follows the angular motion of the beam 
as the tube of the telescope moves westwards. The pipe is fitted with a nut at G, 
into which a square-threaded screw (I G) of four threads to one inch works. The 
telescope can be advanced or drawn back in Right Ascension by the observer by 
turning the screw by means of the pulley I.* A clamping screw in the socket (J), 
through which the end of the screw passes, prevents the screw from turning round 
with the nut when the clock is going. The socket J is bolted to the socket R M, 
L R, and so connected with the telescope. The beam (E F) is faced with strong hoop 
iron. The greater part of the pressure of the beam, pipe, and screw in a direction 
tangential to the circle of motion in polar distance is carried by a lever and counter¬ 
poise attached at N, but not represented. The east end of the screw is turned down 
for a length of two or three inches, and is provided with a washer with rounded edge 
which keeps that end of the screw from lying upon the inside of the tube. Plate 11, fig. 1, 
shows the general arrangement of the screw in elevation, looking northwards, with 
the telescope directed to the zenith; fig. 2 is a cross section of the beam, &c., at G L; 
fig. 3 is a general Anew of the whole on a smaller scale, looking westwards. 
It will be observed that the rate of the clock must be made to vary hi proportion 
to the cosine of declination. No automatic contrivance has been applied for effecting 
this; but, as for obvious reasons we as far as possible restrict our observations on each 
night within a limited range of declination, the alteration of the rate by hand has not 
been found to cause serious inconvenience. 
* This motion is rarely used, as the eye-piece has a motion of 15' or 20' range in an east and west 
direction, by means of which an object can be followed. The small speculum also having a clear aperture 
of nine inches, little or nothing of the pencil of rays is cut off Avithin this range. 
