RAILWAY TRAVELLING AND ELECTRICITY. 
145 
horizontal position, indicating danger , or stop ; the other, the 
arm lowered or depressed, indicating all clear , go on — for each 
line of rails; a switch (fig. 3) by which the electric semaphore 
is worked, a bell (fig. 4), and a bell-key (fig. 5). 
The semaphore is the block signal. The object of the bell is 
to indicate by varying numbers of beats the nature of the signal 
sent or about to be sent. Thus we have for the “ warning 
signal,” “ train coming — look out,” twice two beats — i. e. two 
beats followed by two beats, with a sufficient pause between to 
indicate it is not meant for four consecutive beats. Two beats 
for the 66 departure ” signal, three beats for the “ all clear ” 
signal, six beats for the “ obstruction ” signal, and so on. 
Let us now take diagram No. 1 and follow out the signalling 
of an up and down train. Say we have a train about to start 
from the terminal station a in the direction of b. It is a down 
train. The warning signal is first sent, and acknowledged by 
B. When the train is ready it is started, and its departure is 
notified. The warning signal was twice two beats sounded on 
b’s bell; the departure signal two beats only, b now knows 
the train has left A, and it is his duty to prevent another follow- 
ing till the first has arrived at b. To do this he merely places 
his electric switch (fig. 3) at ON, which raises the electric 
arm for the down line at a to danger. The signalman at a has 
already, on the departure of the train, at the moment when he 
signalled its departure to b, placed his out-door signal for the 
down line at danger, and it has to be retained in that position 
till the electric arm is again depressed by b. No other train 
can now, without disregarding the signals, leave a for b. At 
this moment the position of the signals is that represented for 
down trains in the diagram (No. 1 ) between these two stations. 
The train is running through the section, and is protected in 
its rear at a. 
b, on receiving the departure signal, has warned c that a 
train is coming by signalling to him the twice two beats upon 
I his bell, in the same manner as did a to b. We will now 
assume that the train has reached B. It does its work at the 
station, if it is a station, sets down passengers, takes up others, 
and now it starts towards c, the electric arm for that section 
standing at “all clear.” Its departure is announced, and c 
raises the electric arm at B against any following down train. 
The out-door signal for that line has been placed at danger, and 
now that B is perfectly clear of the train he is at liberty to tell 
a he can send on another train. He does so by placing his 
switch-handle (fig. 3) this time to off, which lowers the 
electric arm at b to the “ all clear ” position, and rings the bell 
three times. The signalman at a then lowers his out-door 
VOL. XV. — NO. LIX. L 
