312 Royal Society :— 
both at sea and on land, and in clear weather to perform in place of 
the needle. 
«Anatomical Description of a Species of Asteroid Polypes, pro- 
bably forming the type of a new genus of Alcyonide.” By John 
Denis Macdonald, Assistant Surgeon R.N. 
March 19.—Dr. W. A. Miller, Vice-President, in the Chair. 
The following communication was read :— 
“A System of Train-Signalling, by which also disabled Trains 
may telegraph for assistance without the aid of portable apparatus.” 
By Charles V. Walker, Esq., F.R.S. 
When, in the early days of telegraphy, messages were sent and 
trains were signalled on the same wires, no facilities existed for 
reducing the apparatus employed for the latter purpose, to a simple 
form. The case is now becoming different, special wires being 
largely devoted to train signals; hence the present system. 
The instrument employed is a large electro-magnet, with a move- 
able armature, carrying a stem and a hammer, which latter strikes 
on a bell by the direct force of magnetism. It is provided with a 
contact-maker, a spring, the depression of which causes a current to 
circulate. The bobbins are 4 in. X 3 in.; and are filled with ten 
pounds of covered copper wire, No. 16 or No. 18. The core is of 
five-eight inch iron. The armature and appendages weigh 21 oz. 
Bells of this kind have been in action for five years without cleaning 
or repairing. The battery is zinc-graphite, and a solution of 1 sulph. 
ac. + 8 or 10 water. The plates, 7}in. X 3 in., are placed in stone 
pots that contain about a quart, the zine standing in a gutta-percha 
slipper, containing mercury. Batteries of this kind will do their 
work untended for half a year and longer. 
The language consists of blows on the bell; the number of blows 
varies according to the train-signal to be given. The distinctions 
required for ordinary purposes being few, the bell-language is very 
appropriate, from its addressing the ear, from its simplicity and from 
the facility with which the signals are given and taken. One blow 
is for the starting of an ordinary train ; two, for an express; three, 
for the arrival of a train ; five, for stopping all trains ; s¢z, for testing. 
This is a general code; other forms of code are used for protecting 
level crossings and junctions; but the fundamental signals of the 
general code are of universal application. This system was intro- 
duced five years ago on the South Eastern Railway ; and at the 
present time consists of about 100 bells, to which additions are in 
progress. 
The bells are connected in pairs, both bells being ina circuit that 
terminates in the earth in the usual way, at each station. The 
signal is made by depressing the spring from its earth-contact, upon 
the zine end of the battery, the graphite end being in permanent 
connexion with the earth. The battery being thus introduced between 
the bell and the earth, a current circulates along the wire and pro- 
duces one blow upon the bell. The home bell may be excluded or 
not from the circuit, when a signal is sent. 
