TEAIN-SIGNALLING IN THEOEY AND PEACTICE. 285 
box tliere_, and labelled Waterloo_, and would see tbe left_, the 
red arm_, up, in sympathy with the white, the right arm of the 
semaphore in the engraving; and the white arm down in 
sympathy with the red or left arm in the engraving ; and the 
signal-man at Blackfriars would make no attempt to signal on 
another up-train until the red arm at his station had been ]3ut 
down by Waterloo. 
The principle upon which the Electro-Magnetic Semaphores 
are here connected up and arranged, is that each station can 
put the white arm only at his own station, and the red arm 
only at the other station, up or down."’^ No signal-man, in 
this arrangement, which may be varied to meet other cases, 
has power to alter the position of his own red arm ; it is 
put up behind a train by the next station, and put down 
when the train is in at that station. 
It win be more convenient here, in explanation of the 
manner of working these instruments, to describe the whole 
process of signalling a train by bell and semaphore ; and we 
can then pass on to the description of the electrical arrange- 
ments that are employed for bringing about the result. 
The ordinary position of the arms of the Electro-Magnetic 
Telegraph Semaphores will be down,^^ that is to say, when 
the hne is all clear of trains, and business begins, say in early 
morning, all the arms will be down, indicating that no 
train is moving. When the first train is ready to start, say 
from Charing Cross, the signal-man will give the proper 
bell-signal to Belvedere on the bell, two, three, or four blows, 
according as the train is for Greenwich, for the North-Kent, or 
Mid-Kent, or for the Main line ; and the Belvedere man will 
acknowledge this by one blow on the bell in reply, and without 
•raising the Charing Cross red or left arm : this is the signal that 
the train may go on ; and when the train has passed, so that 
the Charing Cross man can see the tail lights, he gives the 
out signal a second time, which the Belvedere man acknow- 
ledges, at the same time raising the red arm at Charing Cross 
behind the train, and so protecting it until it has passed him 
at Belvedere, when he signals to that effect to Charing Cross, 
at the same time putting down the red arm there as an 
indication that the line is again clear. While these opera- 
tions are going on for down-trains, others precisely similar, 
but in the reverse direction, are going on for up -trains. The 
separate functions, as well as the combined office of the bell 
and semaphore, will thus be readily apprehended. The bell, 
the basis, as we have said, of all the more sound systems, as 
heretofore speaks to the ear, and asks, not only if a train 
may come, but defines the particular kind of train that is 
ready to come ; and it also tells at the proper time that the 
