458 Description of the Great Southern Telescope. [ Oct., 
produced, which gradually subsides until matters again attain their 
equilibrium. An experiment has been tried with this clock which 
will form a record of its work and a comparison for other clocks. 
The clock was used to give motion to a long ribbon of paper on 
which lines were traced by a pencil worked by a free pendulum in 
a direction at right angles to the motion of the paper itself. The 
result was of course a wave line, the length of each wave being a 
measure of the second as given by the clock. During the process 
at certain points the driving weight was increased from 14 ewt. to 
2, 24 and 3 ewt., but the difference of rate is insensible on the 
diagram, although capable of being measured to the _3,th of a 
second. If this experiment were tried with other clocks it would 
form a valuable record of their work, independent of the testimony 
of their constructor. The shaft which is carried from the clock to 
drive the telescope is severed in one place and a system of six differ- 
ential wheels introduced by which the rate can be rapidly altered 
z,th part, this being the mean of the extreme differences between 
siderial and lunar rate, whilst a small lever and graduated are, in 
front of the clock acts on the governor spindle, moving it up or 
down, and by this means altering the working angle of the balls, 
to make the final correction per lunar rate pro tem. Both of these 
adjustments can be made while the clock is in action. 
It is difficult to understand how in this system of clockwork a 
ereat increase of power (2 to 1) can produce such a small difference 
of rate (,2,), and how the great overplus of power is used up by 
the small increase of velocity. The principle will, however, be 
understood by the following :—Suppose the arms of the governor 
are working at an angle of 45°, and the pressure on the friction- 
wheels to be applied at the same radius as the circle described by 
the centres of gravity of the balls. Then c° = ¢, where ¢? is the 
centrifugal force which will just keep the balls at this angle. Let 
p’, p, and p' be the pressures on the friction-screws corresponding 
to the velocities v°, v, and v'; the centrifugal forces ¢°, ¢, ¢ will 
evidently be as v® : v® : v®, while the corresponding pressures will 
be ae —@:e—2@:¢-—2 ora w— 2:0 — 2:0 — ¢. 
Now if c° = @, the first pressure = 0, whilst if¢ and ¢ be very 
small increments on c°, p’ will bear a very large proportion to p. 
Suppose, for instance, the velocities to be as 100 : 101 : 102, the 
centrifugal force will be as 10,000 : 10,201 : 10,402, and the 
pressure will be as 0 : 201 : 402, so for an increase of 1 per cent. 
in velocity, we obtain double the retarding force in this particular 
instance. 
The hour circles are 34 inches diameter, and covered with a 
band of an alloy of silver and palladium, they are divided to minutes 
of time, and read to seconds by the nonius, the differential reading 
always giving actual AX. 
