TEAIN- SIGNALLING IN THEOEY AND PEACTICE. 
289 
driver on to another road, because be is unable to get any 
visual-signal down, save the one having reference to the road 
he has prepared. The various labels in front of the levers in 
Plate S. have reference not only to the direct line between 
Charing Cross aud London Bridge, but also to the junction 
with the South-Western Railway, as well as to the Cannon- 
Street Road, not yet opened. 
I have already referred to the box in the London yard 
having the greatest number of electro -magnetic semaphores ; 
this box has fifteen levers for working points or switches, 
some of which work simultaneously two pairs of points ; it 
has seventeen levers for arms on the signal-post outside the 
box, and two others for distant signals. In addition to which 
it has seven discs,^^ which work in unison mechanically with 
signals at the neighbouring signal-box, and show how they 
stand. This is a very perfect specimen of a signal-box, and 
illustrates very thoroughly the working of the telegraph 
system as between signal-man and signal-man, and the visual 
system as between signal-man and driver, combined with the 
locking system of levers and the permanent telegraph sema- 
phore signals as between the signal-man and himself. 
At this particular spot roads and cross-over roads form a 
perfect network; but the multifarious points and signals are 
so arranged that before any one of the seventeen arms can be 
lowered on the signal-post, all the points for the particular 
road to which that signal belongs must be properly set; 
aud this haviug been done and the signal lowered, it becomes 
impossible to alter any other points or to lower any other 
signal-arm, that would tend to allow another train to start and 
cross the track of the one already allowed to proceed. 
At the risk of being a little obscure in the absence of a dia- 
gram, I will conclude by giving the routine observed here in ad^ 
mitting, say a Dover train, into and through the London Yard on 
its way to Charing Cross. Call the first box it approaches AB, 
and the second CD ; AB has already been informed, by bell- 
signal, that a Dover train is approaching. He then signals 
it to CD by the bell-semaphore, belonging to the Dover- 
Charing Cross line. If CD is ready to receive it, he first sets 
his road right for it to travel upon, then lowers the proper 
arm on the signal-post ; and, in doing this, he shifts mechani- 
cally a disc in AB box, which indicates what arm he has 
put down ; and, finally, replies to the telegraph- signal of 
AB upon the bell-semaphore, lowering a white arm in his own 
box and a red one in AB. Then, and not till then, AB 
will lower the proper arm on his own signal-post, and allow 
the train to come on. 
The remarks that have hitherto been made have reference 
