28 
THE TELEGRAPH. 
tube 650 yards long between the advanced position at Billan- 
eourt and the fortifications. It was a brass pipe buried in 
the ground, and the orders were sent in the ordinary con¬ 
versational tone, as if the correspondents were speaking to 
each other face to face. Unfortunately, we are not told what 
was the diameter of that tube. 
A speaking-tube does not in general make the sounds audible 
to any but a single person who applies his ear to the bell¬ 
shaped extremity of the tube. 
M. Niaudet, in his work entitled “ Telephones et Phono- 
graplies,” to which we are much indebted, states that he 
remembers seeing, when he was a child, great funnels of a 
foot diameter which were used as the mouthpieces of the 
speaking tubes at M. Breguet’s. These funnels were attached 
to the ceiling of a room throughout the whole of which the 
sounds carried by the speaking-tube could be heard. When 
you wished to reply, you had only to turn towards this mouth¬ 
piece and to speak more or less loudly according to circum¬ 
stances. During the day, the external noises somewhat 
confused the results, but in the silence of the night the least 
noise made in the communicating room was heard at the other 
end, as for instance, when the pages of a book were turned or 
when a pen was scratching on paper. 
It will be seen that we should be aware of speaking-tubes, 
for sometimes they allow what is said in the room from 
which they lead to be heard by a person for whom it is not 
intended. 
Speaking-tubes are always fitted with a whistle for calling 
the correspondent. Nearly every telegraphic arrangement 
requires some method of calling the attention of the person 
who is to receive the message. The optical telegraphs are the 
only ones without this means of preliminary warning, and they 
therefore require a continued attention to be directed towards 
the point from which the signals proceed. 
The electric telephones having been completely described in 
other works, we do not here intend to do more than explain 
the principle of telephonic apparatus, and describe the practical 
systems which are already used by the Telephone Companies at 
New York, London, and Paris. 
As regards history, we may state that in 1844, Page found 
