146 
POPULAR SCIENCE REVIEW. 
signal to the same position, and all is ready for a train to 
follow. 
Up trains are dealt with in a precisely similar manner. We 
have an up train running betwen c and b. At c we observe 
the electric signal for up trains shows danger, and the out-door 
signal the same ; the signals in advance are at “ all clear.” 
When the train has arrived at b, done its work and departed, the 
section b c will be cleared, and c will be able to send on another 
train. 
On single lines, that is lines which have only one set of rails 
on which both up and down trains are worked, additional 
precautions are taken. Before the train starts from any signal 
station the section is blocked against any train approaching in 
an opposite direction. It then leaves, and the station in ad- 
vance of it blocks it in the rear. It is thus protected in advance 
and behind, section by section, throughout the line. 
The operation of signalling, although somewhat tedious in 
description, occupies but a very little time ; the pressure of a bell- 
key and the touch of the switch-handle are all that is required. 
The instruments are arranged in the most convenient manner 
over the signalman’s frame, so that he can even carry on his 
electric signalling by one hand whilst with the other he operates 
the levers working the out-door signals. So rapidly is all 
this performed that trains frequently follow over busy sections 
of line within two and three minutes of each other. The 
sections are of course regulated to the traffic. Where it is 
dense they are necessarily short, the limit being the distance 
sufficient to enable a train to pull up before reaching the next 
signal station. Thus there are, in places, sections as short as 
half-a-mile, whilst in others they are five miles in extent. 
But apart from the protection which electricity imparts to 
railway travelling, and the facility it offers for adjusting and 
regulating the traffic, there are innumerable purposes for which 
the telegraph is employed to facilitate business and to secure 
efficiency. The distribution of correct time, the collection of 
spare trucks and coaches, the relief of staff, the supply of assis- 
tance in cases of accident and danger, and — not least — the 
reparation of the errors and thoughtlessness of passengers. 
It is used on some lines to establish an effective means of 
communication between passenger and guard ; and perhaps one 
of its most useful applications is to record in the signal box, 
before the signalman’s eyes, the position of the signal-arm by 
day and the condition of the light by night, which is hidden 
from his sight by the formation of the line, buildings, darkness, 
fog, or steam. Electric repeaters are one of the greatest ele- 
ments of safety in working railways. Fig. 6 represents an 
arm and light repeater combined. A battery is placed in the 
