76 
THE TELE GRA PH. 
and telegraphic departments. This mode of despatch has been 
called by the Germans “ the tubular post.” 
We have already seen that the utility of the electric tele¬ 
graph is, for short distances, relatively less than for great dis¬ 
tances ; for the absolute speed of the electric transmission is 
almost independent of the distance. For short distances, trans¬ 
mission by compressed air has, therefore, obvious advantages 
over electric transmission ; because it allows many telegrams 
to be sent simultaneously, whilst with electric apparatus, the 
sending of telegrams, that is to say, the signs and words, can 
take place only in succession. 
The number of offices in the tubular post system at Berlin, 
which was at first fifteen, now reaches twenty-three. These 
offices supply the most important parts of Berlin, and are con¬ 
nected with the central telegraph station and with each other 
by pneumatic tubes, the total length of which is twenty-four 
miles. The air, compressed and rarefied, is supplied by six sets 
of apparatus, in each of which two steam-engines work the 
several air-pumps. The velocity of transmission is about 1,086 
yards per minute. 
The cost of laying down the whole system at Berlin was 
2,736,700 marks, including the purchase of land. 
By means of the pneumatic tubes, letters and post-cards can 
be delivered one hour after having been posted, within the 
limits of the interior district. The tubular post is used also 
for distributing the telegrams arriving at Berlin, and those 
sent from the central office. It is also used for the despatch of 
packets and letters to the railway stations when the hour of 
departure of the trains is too near to allow of the ordinary modes 
of transport being used. Similarly the tubular post is used for 
communications arriving at Berlin. 
The mean number of despatches in 1877 and 1878 was at the 
rate of 1,500,000 per annum. 
The utility of the tubular post is so well recognised in Ger¬ 
many that the government is desirous not only of extending 
the system in Berlin, but of providing other towns with this 
advantageous mode of communication. 
The Compressed Air Telegraph. —The pressure of air 
also supplies a means of making signals at short distances by 
means of very slight compressions through narrow tubes. We 
