TE AIN- SIGNALLING IN THEOET AND PRACTICE. 279 
of them is wound about five pounds of large size cotton-covered 
copper wire ; a rod of iron is bent into a sort of (J -sliape_, and its 
arms are thrust through the bobbin from behind^ their ends 
being fiush at the front. Facing the ends of this iron core is care- 
fully pivoted the plate, or keeper, of iron, visible in the figure, 
carrying a slender rod, to which is affixed a hammer ; a large 
bell, 3 to 6 inches, or more if needed, in diameter, mounted 
on a stem, completes the instrument. This is the Train- 
Signal BelP^ that has been on the South-Eastern Railway since 
December, 1851 ; and of which, at the present time, about 
400 are in daily and constant use for the sole purpose of sig- 
nalling trains on the 308 miles of which that railway consists. 
This instrument, and the manner in which it is employed, are 
more than typical of train- signalling generally, and are the 
best illustrations that can be selected of the system. The 
instrument itself, more or less modified in construction — never 
larger or more powerful, almost invariably on a smaller scale 
— and the language educed from it, are at the foundation of 
all the best-devised systems, — the systems that, one by one, 
during the last few years have cropped up on the best-con- 
ducted railways. In the majority of cases further appliances 
are introduced, the nature of w hich will be given in the sequel ; 
but the bell and the bell-signals are the substance and founda- 
tion of the whole, and the systems would be impracticable — 
would fall through, if these signals were withdrawn. 
The action of the bell is very simple, and may be anticipated 
from what has been already said. When a current of electri- 
city traverses the coils, the U-shaped iron core becomes a 
magnet; and of course has the well-known property of attract- 
ing iron, in virtue of which the iron plate, or heeioer, as it 
is called, is drawn forward, carrying with it the stem and 
hammer, and causing the latter to strike loudly upon the bell. 
When the electricity is cut ofi*, the magnetism ceases, and the 
keeper recedes, assisted by a spring, visible in the figure. If a 
second and a third current of electricity are successively sent, 
a second and a third blow will be given on the bell, and this is 
the bell-language : one blow has a meaning of its own ; two 
blows have a different meaning ; three, still a different ; and so 
on. The requisite number of currents of electricity are sent 
by a very simple action : a spring or key is pressed down, 
like the key of a piano-forte, one or more times, according to 
the number of signals required to be made. A spring of this 
kind is shown on the right side of the bell (fig. 2). The sound 
of the beU can be heard at a great distance. 
In order to illustrate the laws of train- signalling, it will be 
better to take the simple case of a railway like the Ramsgate- 
Margate, for instance, having two pairs of rails, an up line and 
