284 
POPULAE SCIENCE EEVIEW. 
It has been further thought advisable, especially where the 
trains up and down are very many in number, that the signal- 
man should be reminded by some signal visible to the eye 
that he has given or taken a certain bell signal ; and this 
visible signal is further turned to account by being used in 
combination with the audible signal ; and thus diminishing 
the number of sounds necessary for carrying on the traffic. 
The visible signals at a glance show the actual state of the line,, 
whether a train is coming or not, whether a train is still going 
on or is safely in ; in fact, whether the lines in either direction 
are free or not of trains. 
The Charing Cross Bailway, where a system of this kind has 
been in full operation since the opening, will give a very perfect 
illustration of the joint service of the eye and ear in interpret- 
ing what the hand has given. 
Plate XI. shows the manner in which the signal-box at 
Waterloo is fitted up. This box is intermediate between Bel- 
vedere Bead and Blackfriars. At the front of the box, in the 
right and left-hand corners respectively, are placed a bell and 
an ‘’^Electro-Magnetic Telegraph Semaphore.’’"’ Externally, this 
instrument presents to the eye a signal-post on a small scale, 
similar to those in use on the railway in question, with a red 
arm on the left side and a white arm on the right side, in like 
position with those on an actual signal-post, and capable of 
being moved, by an electric current, indicating danger, or 
down, indicating caution, as required. And the regulations for 
working them are such that the arms at all times indicate the 
state of the line. Looking toiuards a semaphore, whether actual 
or electro -magnetic, the red and left arm has reference to trains 
receding ; the white and right arm to trains approaching ; and 
when an arm is up it indicates that a train is on the line, and 
when down that a train is not on the line. So that, looking at 
the position of the arms as they stand in Plate XI., it is 
evident that no train is going from Waterloo to Belve- 
dere, and no train is coming from Belvedere to Waterloo; 
both lines on this side of Waterloo are clear. On the other 
side, there is no train going from Waterloo to Blackfriars; 
but a train is on its way from Blackfriars to Waterloo. 
These semaphore instruments are connected up in pairs ; the 
one on the right hand of the signal-box is connected with its 
companion at Blackfriars, and works in sympathy with it, the 
arrangement being, that the red arm at one station and. 
the white arm at the other station work up and down 
together. When the red arm at one station is up, the white 
arm at the other is up also ; when the one is down, the other 
is down.^^ If an observer were at Blackfriars, he would find 
the companion semaphore in question on the left side of the 
