=The Berlin Pneumatic Telegraph.=—In 1863 the Prussian government applied to the firm of Siemens and Halske, of Berlin, for a proposition to establish a system of pneumatic tubes in that city for the transmission of telegraph messages. A proposition was accordingly submitted, and the work was completed in 1865. This first line consisted of two parallel wrought-iron tubes, two and one-half inches in diameter, one tube being used exclusively to send in one direction, and the other in the opposite direction. They extended from the telegraph station to the Exchange, requiring a total length of five thousand six hundred and seventy feet of tube. The two tubes were looped together at the Exchange, and a continuous current of air was made to circulate in them by a double-acting steam air-pump, located at the telegraph station. Air was compressed into one end of the tube and exhausted from the other. With nine inches of mercury pressure and vacuum the passage was made in ninety-five seconds to the Exchange, and seventy-five seconds from the Exchange. It was similar to the line established in London by the same firm some years later, which we have already described, except that there was no intermediate station. After the line had been in use for a year and a half, the Prussian government had it extended, first, from the telegraph station to the Potsdam gate, with an intermediate station at the Brandenburg gate. After these preliminary experiments, further extensions were made until a net-work of tubes extended over the city of Berlin, including no less than thirty-eight stations and over twenty-eight miles of tubes; but in laying down this net-work a departure was made from the Siemens system. Air was no longer kept constantly circulating, but power was stored up in large tanks, some being exhausted and others filled with compressed air, which was used when required to send messages, usually at intervals of five or fifteen minutes. The exhausted tanks were permanently connected with the closed tubes, which were opened when required for use. The tanks containing compressed air were connected to the tubes when messages were sent. The internal diameter of the tubes was 2.559 inches. They were laid in circuits, including several stations in a circuit, and the carriers travelled only in one direction around the circuit. Some outlying stations were connected by a single tube with central pumping-stations, these single tubes being worked in both directions. Years of experience have shown the disadvantages of this circuit-system, and it has gradually been changed to the radial system, such as is used in London, until now nearly all the stations are grouped around the central pumping-stations, to which they are connected directly by radiating tubes. The Siemens apparatus has been replaced by simpler and less expensive valves and receiving-boxes, the latest form of which was designed and patented by Mr. Josef Wildemann. [Illustration: FIG. 3.