Grupp— Time Signats. 45 
In the normal state, the contact of this arm with the silver-shod dise 
- occurs in the break between the two silver rings, where a small piece of 
agate is inserted; but if the shaft AA has revolved too quickly or too 
slowly, and thus has necessitated an alteration of the position of the disc 
No. 7, the contact finger moves off from the agate block to one or other 
of the silver half-rings which forms an electrical connexion with the 
accelerator or retarder, d or a’. These remain sufficiently long in action 
to correct the error and bring the contact pin on to the agate block once: 
more. 
By this means, which is practically the same as what I have used 
with such success for many years past on my equatorial telescopes, I can 
ensure that the corrected portion of the apparatus on the shaft AA keeps: 
time as accurately as the standard clock which controls it. 
BB is a second shaft worked from the first by a pair of wheels of 4 
to 1, and revolves once ina minute. This second shaft is supplied also 
with a pair of correctors and a checking arrangement worked, so far as 
this is concerned, only once in 24 hours, through a relay which receives 
the Greenwich signal. There isno occasion to describe this second shaft, 
as it is practically identical with the first, its duty being to remove, every 
24 hours, any difference that may exist between the time given by the 
standard clock and that of the Greenwich signal. Without this second 
shaft, the rate of the clock would be exactly that of the rate of the 
standard clock which controls it, and which would, no doubt, be excellent 
day by day; but the reception of the Greenwich signal and the automatic 
corrrection of it by the apparatus on this second shaft ensures that this 
clock will never be different from the true time as emanating from 
Greenwich by a quantity greater than what the standard clock errs in 
24 hours. 
Fig. 5, Plate V., shows a modified arrangement of fig. 2, by which 
the accelerator is dispensed with. The clock is given a slight gaining 
rate, and, consequently, it is only necessary to provide a retarder. 
Fig. 6, Plate V., shows the suggestion for recording the amount of 
error in the standard clock every day. A tape of paper is arranged to 
pass round a roller which, in a general way, is not in contact with any- 
thing on the reyolying shafts, but if either the accelerator or the retarder 
comes into action for any given number of seconds (say 5 or 6 seconds), 
this roller carrying the tape is pressed against another roller on the 
revolving shaft, and a capillary tube filled with ink draws a mark upon 
the tape, the length of which corresponds to the amount of correction 
which has been necessary to bring the clock into synchronism with 
Greenwich. Two of these capillary tubes would be provided, one to 
show the + error, and the other the — error. 
