April 6, 1871 | 
NATURE 
45° 

Company, he employed compressed air to drive carriers 
to out-stations, and a vacuum to bring them back again. 
When a vacuum is employed, the carriers are driven by 
the ordinary atmospheric pressure only of fifteen pounds | 
to the square inch, but when condensed air is employed, 
almost any pressure may be applied, so that the carriers 
can be driven with enormous velocity. He also substituted 
felt for gutta-percha carriers, since the latter were some- 
times partially melted by the heat occasioned by friction, 
and coated the insides of the pipes with sticky matter. 
Further, he designed some pneumatic valves ; the carriers, 
on arriving at the end of their journey, were made to | 
strike against a brass button, the motion of the button 
set a valve to work, the valve opened the door of the 
chamber at the end of the pipe, the carrier then fell out, 
and dropped down on the table below. 
were made to let themselves out when they arrived at the 
end of their journey, by which plan much hand labour on | 
the part of assistants was saved. These improvements 
worked well, and are working well at the present time. 
Seven or eight City telegraph stations have been thus 
pneumatically connected for many years. 
But a further improvement in the system has been made 
within the past year or two by Mr. C. W. Siemens. He 
lays down the pipes in circuits, and has pressure in the 
rear, and a vacuum in front of each carrier, so that as the 


motive forces all act in one direction, there may be 
several carriers flying through the tubes at the same time. 
If these carriers were not stopped anywhere, they would 
all find their way back to the central station. He has in- 
vented also a “shunt,” whereby any intermediate station 
can stop its own carrier, and pick it out of the tube with- 
out interfering with the motion of other carriers which 
may be flying through other parts of the circuit. _Sup- 
pose the carriers to be three minutes apart in point of 
time, and that five stations are on the circuit, each station 
knows at what time its own carrier is due, so is able to 
take it out without interfering with other carriers. If the 
carriers be not sent at regular intervals of time, the re- 
ceiving station can be told when its carrier is started, by 
telegraph. The plan of picking out the carriers Is simple, 
and the principle may be explained by the aid of the 
accompanying diagram. A B is the main tube, and the 
direction taken by the carriers is denoted by the arrows ; 
K K and N N are metal plates, between which the two 
short tubes D D and E H slide in an air-tight manner. 
These two short tubes are attached to a lever joint. When 
the assistant does not wish to intercept a carrier, the 
tube D D is left in the place occupied by the tube E H 
in the cut, and D D being open at both ends, carriers 
pass through it without interception. Upon sliding E H 
Thus the carriers | 


into the gap in the main tube, however, the carrier is 
stopped by it. It is brought to a standstill very gently, 
because it compresses some air in front of itself, which 
air issues with restricted freedom through the hole H ; 
| thus the carrier makes for itself an air-cushion to break 
the violence of the blow. When the carrier is caught, the 
tube D D is brought into the line of the main tube, 
after which an air-tight door in the side of E H is opened, 
and the captured carrier, with its messages, is taken out. 
For short distances to and from telegraph stations near 
the Bank and the Post Office, the pneumatic tubes are 
from one-and-a-half to two-and-a-half inches in diameter ; 
they vary in diameter according to distance. But the one 
large Siemen’s circuit at present laid in London goes from 
Telegraph Street to Charing Cross and back, the General 
Post Office and the Temple Bar Office being the inter- 
mediate stations; this pipe is three inches in internal 
diameter. The carriers travel at the rate of about a mile 
in three minutes, but the rate varies with the pressure. 
It may be asked why these pneumatic tubes are useful 
in connection with telegraphic offices? The fact is, that 
there are many disadvantages in sending messages very 
short distances by the electric telegraph. Suppose one 
telegraphic wire be suspended between two stations half a 
mile apart, and another be suspended between two stations 
three hundred miles apart ; let thirty messages be received 
all at once for transmission over each of these two wires, 
it is plain that some of these messages will have to wait 
half an hour before their turn comes to be signalled over 
the wire. The public will not complain of a delay of half 
an hour in the delivery of a message in a town three hun- 
dred miles off, but they would make a great outcry if a 
message took half an hour to go half a mile by the electric 
telegraph. Therefore, it is the simplest and most expeditious 
plan for the central telegraph station in a great city to 
blow the messages bodily through tubes, to branch stations 
not far off ; the plan saves time and saves labour. Com- 
plaints published in the newspapers about delays in tele- 
graphic messages, refer for the most part to telegrams 
sent from one part of London to another, and the delays 
are often caused by the pressure of a sudden influx of 
work upon particular wires. WILLIAM H. HARRISON 


NOTES 
WE learn that the volume containing the various observations 
of the recent total eclipse will be edited by the Astronomer 
Royal, 
Ir is stated that Mr. Abel, Prof. Ramsay, and Mr. Huggins, 
have been invited to lecture this year to the members of the 
British Association at the forthcoming meeting at Edinburgh. 
THE meeting of the Royal Colonial Institute on Monday is 
likely to have a practical result. The paper read was by Mr. 
Hyde Clark on the ‘‘ Appointment of a Reporter on Trade 
Products for the Colonial Office.” After an interesting -dis- 
cussion the President, Lord Bury, M.P., on the part of the 
Council, proposed that a Committee should be named to apply 
to the Secretary of State for the Colonies for such a department, 
and for the provision of a Colonial Museum on the same ta is 
as the department provided at the India Office for India. 
Ar the last anniversary meeting of the Chemical Society it 
numbered 551 ordinary members and 36 foreign members. 
Six of the former have withdrawn from the Society,—on the 
other hand forty-two new members have been elected into the 
Society. It has lost five ordinary members by death, viz., Mr. 
George Jolley, Dr. W. A. Miller, Dr. Aug. Matthiessen, Dr. 
J. S. Muspratt, and Mr. W. W. Rouch; and the deaths must 
also be recorded of two foreign members, viz., Prof. Gustav 
Magnus and Prof, Weltzien. The election of the president, the 
officers, and the other members of Council for the ensuing year 
