PNEUMATIC TELEGRAPHY, 
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at that time 2,022 yards, but since 1865 a second circuit having 
a length of 4,064 yards has come into use. The offices it con¬ 
nects are, in addition to the Central Telegraph Office, those of 
the Potsdamer Thor and the Brandenburger Thor. 
The same system was, with some modification of the details, 
applied in London in 1870. As pneumatic tubes on Clark’s 
system, modified by Varley, as well as some on Siemens’ system, 
are now working in England, we shall further on give a detailed 
description of them. 
At Paris, pneumatic tubes came into use in March, 1867. 
The apparatus erected in the office in the Rue Boissy-d’Anglas 
was composed of three iron-plate vessels ; one for water, of the 
capacity of 1,540 gallons, and two for air, holding 240 cubic 
feet. Communications could be established at will between 
these three vessels, and the tube through which the messages 
were sent was joined with one of the air-vessels through a pipe 
provided with a stop-cock. With the water vessel were con¬ 
nected a pipe conveying the town water, and another pipe for 
discharge. By admitting water into one of the vessels until it 
was completely filled, the volume of air contained in the three 
vessels was reduced from 6,580 cubic feet to 4,134 cubic feet, 
and the internal pressure became therefore equal to 1*6 atmos¬ 
pheres. Compressed air propelled the carriers in one direction, 
and motion in the other direction was caused by allowing the 
water filling one of the vessels to flow away, so as to produce 
a partial vacuum. The system was very simple in its arrange¬ 
ments ; but it could only be used where a sufficient and cheap 
supply of water was at hand. In the course of the year 1872, 
however, the French government substituted steam-engines for 
these air-compressing water vessels. 
In London the pneumatic tubes all go to the Central Tele¬ 
graph Station where the steam-engines are placed. Mr. Clark’s 
original system now remains only in one direction, between two 
rooms in the central offices, namely, the Provincial Gallery, and 
the Intelligence Department. It is thus arranged :— 
A lead pipe of f-in. diameter connects these two offices. 
The one or the other end of this tube can at pleasure be put in 
communication with a vacuous vessel. When one of the offices 
desires to send a carrier, the latter is placed in the tube, and 
a signal is made to the other office to open the stop-cock 
