GREENWICH TIJIE AND ITS TELEGRAPHIC DISTRIBUTION. 359 
especially the laying of the first submarine cable, became early 
desirous of placing the Eoyal Observatory in communication 
therewith, to be prepared to meet the scientific demands likely 
then to arise, as well as to be ready to supply any possible 
public demand for Greenwich time. How at last the time- 
signal system came to be proposed the Astronomer Royal him- 
self is scarcely prepared to say: it was, as he expresses it, 
“ partly in conversation, partly in other ways ; but to Mr. C. V. 
Walker, Mr. Edwin Clark, Mr. Latimer Clark, and afterwards 
Mr. C. F. Varley, is the existence of the system due.” After 
some correspondence, the Astronomer Royal, in the year 1852, 
obtained permission from the South-Eastern Railway Company 
(on the representation of Mr. C. V. Walker, their telegraphic 
engineer) to erect wires on their railway, for the purpose of 
obtaining communication with London ; and special apparatus 
being provided, the system of signalling time from the Obser- 
vatory was commenced. We shall not, however, further follow 
the subject historically, but proceed to describe the system as 
it now exists. 
As respects, now, the time-distributing apparatus, the clock 
specially erected at Greenwich claims first attention. This 
clock, the normal mean-time clock of the Observatory (erected 
in the year 1852), is kept adjusted as nearly as possible to 
Greenwich mean time. It is maintained in action (on Shep- 
herd’s plan) by galvanic power alone. When its pendulum (a 
seconds pendulum) swings to the right, a galvanic circuit is 
closed, which causes an electro-magnet to raise a small weight. 
This being discharged on the pendulum in its swing to the 
left gives it a small impulse, which, repeated at each swing to 
the left, suffices to maintain it in action. Other galvanic 
circuits, closed, one as the pendulum swings to the right, 
another as it swings to the left, allow galvanic currents, alter- 
nately positive and negative, to pass to a pair of electro-magnets 
placed above it. These currents cause the electro-magnets 
to attract and repel alternately certain bar-magnets, giving 
thereby a reciprocating motion to the axis which carries them. 
An anchor on the axis gives forward motion to a wheel 
carrying the seconds hand, from which, by a simple train of 
wheels, motion is communicated to the minute and hour hands. 
So far as concerns the normal clock proper. But if the wire 
which passes from the pendulum to work the hands is afterwards 
led (before being returned to the battery) to other electro- 
magnets in different parts of the building, each pair similarly 
working hands on a dial, the hands on all will advance together, 
their forward movement depending entirely on the galvanic 
current let off at each second by the one pendulum, which con- 
sequently governs the whole system. There are within the 
