Mr. C. V. Walker on a System of Train-signalling. 318 
By the above arrangement signals are sent from station to station. 
But the extreme simplicity of the battery, the bell, and the language 
allows the arrangements to be so modified that signals may be made 
on a pair of bells from any joint, intermediate between two bell- 
stations, without the necessity of providing the signaller with any 
telegraph or battery, or any electrical apparatus whatever. The ad- 
dition of this property to the bells does not in any way interfere 
with their being in perfect action and constant use for the ordinary 
work of train-signalling, and therefore if the guards of trains and 
the plate-layers of the permanent way are provided with a signal for 
expressing their wants, a great advance is made in telegraphy, and 
a large element of safety is gained for the travelling public. 
It is well known to electricians that, if two equal and opposed 
currents are presented to the respective ends of a wire, no evidence is 
manifested of the circulation of electric force; the wire is in a null 
state, as much so as if no current was presented to it. Taking ad- 
vantage of this law, in connexion with the simple bell-system above 
described, the circuit is made to contain the two batteries, one at 
each station, as well as the pair of bells; the same pole, the graphite, 
for instance, of each battery being connected with the earth. 
When the home-station signaller desires to make a signal, he 
depresses the spring as before; but the connexions are such, that 
by this act he excludes his owz battery from the circuit. The circuit 
then contains but one battery,—namely that at the pass station; the 
current of which is now able to circulate from end to end, being no 
longer counterbalanced by an equal and opposite current ; and con- 
sequently the bells are sounded. This, then, is the process for ordi- 
nary train-signalling, under this arrangement. 
By altering the contact-maker so that it inverts the battery in the 
circuit, instead of putting it out of circuit, both batteries are made 
available for each signal; and consequently the power and with it the 
cost of each may be reduced. 
But the null state of the wire is equally well and very readily 
destroyed, by connecting it with the earth at any point intermediate 
between the two stations; for by this process a complete circuit is 
made or channel opened for the discharge of both ends of both 
batteries, each independently of the other, except that the attached 
wire between the earth aud the telegraph wire is common to both 
circuits, and thus the bells at the respective stations are actuated by 
the batteries of the respective stations. If ten blows with a pause of 
a minute, and then ten more, is the signal that the engine is disabled ; 
ten blows, anda minute of contact, that an accident has happened ; a 
ringing continued beyond ten, that the permanent way is obstructed, 
the stations at either side are advised and can take the measures 
necessary to meet the case. 
These contacts may be made by hooking a wire or rod on to the line 
wire and making the necessary contacts with the rail; or, which is 
better, by establishing contact-makers, properly secured at frequent 
intervals on the telegraph posts. 
This system gives to those in charge of disabled trains a certain 
