More success has attended the introduction of a system for transmitting small rolls of paper through tubes of a few inches diameter, by pneumatic pressure: Mr. Siemens introduced it at Berlin; it was next tried with success at Paris; Mr. Latimer Clark con structed similar apparatus iu London; and the plan is now in regular use in the tele graph department of the new buildings connected with the general post-office in St. Martin's-le-Grand, while it is also used in some of the chief provincial cities and towns. In 1875 the number of tubes in London was 24. with an aggregate length of nearly 18 ni.; there were 4 tubes in Liverpool; 3 in Dublin ; 5 in Manchester; 3 in Birmingham; and 1 in Glasgow. Small tubes, two or three inches in diameter, are arranged for the reception of telegraph forms or papers, made up into a roll, and put into a felt cylinder. The purpose is to economize time and expense in conducting the government postal tele graph business by blowing along the telegraph forms at a rate of 30 in. an hour, instead of sending them by street conveyance. Two parallel tubes have been laid down beneath the pavements of the streets from the general post-office to various parts of London, and also in some of our large provincial cities and towns; additions being made to the length of tube according as the system becomes practically developed. One tube in each pair may be called the down miae, the other the np ; the two are placed in connection at each end. and one steam-engine works them both. Time felt cylinder very nearly fills up the tube. lint still moves easily along it: this movement is brought about either by the for mation of a partial vacuum in front of the cylinder, or by compressing the air behind it; and the steam-power is so applied as to produce either or both of these two results, according as convenience may suggest. An ingenious plan is adopted for accommodat•
Mg one or more intermediate ollices. just as local stations are accommodated between the two termini of a-railway. The cylinder or carrier travels from end to end of the tube, unless a block or check action is purposely put in force at an intermediate station; and the mode of effecting this is one of the most beautiful of Mr. Siemens's inventions relating to the subject. Two pieces of pipe, the ?Tearer and the transmitter, are made exactly alike, and are so pivoted together that either may be adjusted into a cavity cut in the tube, and made temporarily to form part of it. The carrier, we will suppose, is intended to stop at the intermediate stations, to admit of the removal of some telegram papers and the introduction of others. A click is heard; the carrier strikes against an obstruction iu the receiver; the cavity is opened; the exchange of papers is made; the carrier is re-introdueed, but into the transmitter instead of the receiver; the cavity is closed again, and the carrier resumes its jouruey, All this is the work of a few seconds merely. If the intermediate station has nothing to send and nothing to receive, the transmitter alone is used, and the carrier travels on without stopping. The up-tube and the down-tube have each its apparatus of receiver and transmitter. The felt cylinder and its contents being very light, a slight rarefaction of the air in front of it, or conden sation of the air behind it, is sufficient to produce a speed equal to twenty or thirty m. an hour. Practically, there is a current of air maintained, circulating through the two tubes and their terminal connections; wherever a carrier is placed in this current it is blown along, and there maybe two or more carriers traveling at the same time. .