144 
POPULAR SCIENCE REVIEW. 
Both divisions consist of several companies or sections, each of 
which contains about 150 men, including officers, telegraph 
operators, pioneers, workmen for the erection of the line, and 
drivers for the station-, store-, and baggage-waggons. In all 
armies the telegraph and materiel is, of course, very similar, 
and we shall therefore describe that of the Prussian army, 
adding a few notes on that of other countries. 
The two essential portions of the field telegraph are the 
station and the line. In order that there may always be a 
sheltered place for erecting the instruments and transmitting 
messages, each detachment of the telegraph corps carries with 
it one or more waggons fitted up as stations ; but wherever a 
halt of more than a few minutes is made, and there is a suit- 
able building available for that purpose, a telegraph station is 
established in it bv removing the batteries and instruments 
from the waggon. Fig. 1 (Plate CVIII.) is an outline sketch of 
a Prussian station- waggon ; fig. 2 being a section of the same. 
The waggon is about 9 ft. long, with an interior height of 
4 ft. 6 in., and a width of 4 ft. It is built as lightly as pos- 
sible, and weighs when loaded only 14 cwt., and is easily 
drawn by two horses. On the outside are two insulated brass 
conductors ( i , fig. 2), to which wires can be attached. Inside 
the windows is a shelf with a drawer (cZ), on which the instru^ 
ment ( t ) can be placed when in use, and opposite to this is a 
seat or bench (s) for the operators, on which a man can sleep at 
night. Under the seat is a recess in which a spare instrument 
(t) is kept, while the batteries are arranged in a box (b ) under 
the shelf. When a message is to be sent from this movable 
station the waggon is stopped, and the line-wire is attached to 
the insulated conductor (i). This is connected with the 
instrument and battery, and in order to complete the circuit 
the battery is placed in electrical communication with the 
second insulated conductor, to which another wire is attached 
which joins it to the earth-conductor or earth-stake ( 'piquet a 
terre) (fig. 5). Thus the course of the current, when trans- 
mitting a message, is from the battery to the instrument, and 
by the first insulated conductor ( e , fig. 2) to the line of wire, 
the earth-plate of the receiving station returning it to the 
earth-conductor, driven into the ground near the waggon, and 
thus back by the second insulated conductor to the battery. 
The instruments are of the Morse pattern, constructed so as 
to fit in a very small space, and recording the signals with ink. 
The battery (of which there are two in each station-waggon) is a 
simple form of M. Marie Davy’s sulphate of mercury battery. 
It consists of ten elements, one of which is shown in section in 
fig. 8 ; (c) is a charcoal vessel, containing sulphate of mercury 
moistened with water to the consistency of paste, and in this 
