44 Scientific Proceedings, Royal Dublin Society. 
EXPLANATION OF PLATES IV. AND Y. 
In Plate IV., AA is a shaft which is in direct connexion with the 
15-seconds shaft of the uniform motion clock, and revolves approximately 
at that rate. 
A toothed wheel, No. 1, is fixed upon this shaft; all the other wheels, 
with the exception of Nos. 7 and 8 at the other end, are loose upon the 
shaft. 
Wheel No. 2, which is cast in one piece with No. 3, is cut with a 
slightly different number of teeth from No. 1, and is driven from it by 
means of the pair of pinions, yp, which act as couplers so long as the 
rate is normal; if, however, the disc 6’6’ is arrested momentarily, the 
motion is conveyed from No. 1 to No. 2 through the pinions yp, and 
consequently a slight differential rate is produced, as Nos. 1 and 2 have 
not quite the same number of teeth. 
The same description applies to Nos. 3 and 4, the result being that 
a momentary stoppage of the disc 4 d causes a slight acceleration of the 
rate of the rest of the moving parts, including wheel No. 6; whereas a 
momentary stoppage of 0’ d’ causes a slight retardation. 
No. 6, shown in black, is an ebonite ring, mounted with a pair of 
nearly half circles of silver shown enlarged in fig. 4, Plate V. 
No. 7 is alight metallic dise with a notch or notches, better shown in 
figs. 2 and 4, Plate V. 
(c) is an electro-magnet with an armature better shown in fig. 2, 
Plate V. This armature is worked from the sealed or standard clock 
through the relay (f), shown enlarged in fig. 8, Plate V., and the tooth 
of the armatures of this electro-magnet engages into the notch on wheel 
No. 7, and will not allow that wheel to revolve so long as it is engaged, 
A current is sent into the electro-magnet (c) every 15 seconds from 
the standard clock. Ifthe uniform clock has gone correctly, that current 
occurs at the moment that the V notch comes opposite the V on armature. 
If the uniform motion clock has gone either fast or slow, the notch will 
not be exactly opposite the tooth; but when the current arrives, the 
impact of the tooth on the side of the V notch, in wheel No. 7, sets that 
wheel, which is driven only by friction, backwards or forwards the 
necessary quantity. 
By means of this device, the revolutions of the disc No. 7 are con- 
trolled from the standard clock, and kept in an exact uniformity at every 
15 beats of the pendulum. 
Fig. 4, Plate V., shows that the disc No. 7 has mounted upon it a 
small arm which plays round the silver half rings on the ebonite disc. 
