DIAGRAM OF PART OF PARIS PNEUMATIC TUBE SYSTEM. PARIS CIRCUIT SYSTEM.] =The Paris Pneumatic Telegraph.=—We will now glance at the system used in Paris, which has some novel features. In 1865 it was decided to establish a system, and the first experimental line, from Place de la Bourse to the Grand Hôtel, on the Boulevard des Capuciens, was laid in 1866. Instead of using a steam-engine to drive an air-compressor or exhaust-pump, air was compressed in tanks by displacement with water from the city mains. In 1867 this line was extended to Rue de Grennelle St. Germain, with an intermediate station at the Rue Boissy d’Anglais, and another line with stations at Rue Jean Jacques Rousseau, Hôtel du Louvre in the Rue de Rivoli, the Rue des Saints Pères, and terminating in the central station. In 1868 the system was changed to a polygonal or circuit system by removing the station in the Rue de Rivoli to the Place du Théâtre Français and connecting the latter directly with the Bourse. Other changes and extensions were made in 1870 and 1871, until three polygons or circuits were formed, with five or six stations in each circuit, and several outlying stations were connected by independent tubes. In the middle of the year 1875 seventeen stations had been connected and plans were made for twenty-one more. Instead of maintaining an air-current around each circuit by machinery located at one of the stations on the circuit, at least three of the five or six stations comprised in the circuit have means of supplying compressed air or of exhausting it, and each side of the polygon, or section of the circuit between two stations, is operated independently of the rest of the circuit (see Fig. 3). Carriers are sent on from station to station around the circuit, either by compressed air from the last station from which they were sent or by means of exhaustion at the next station towards which they are moving. The carriers are made up in trains of from six to ten, with a piston behind them that fits the tube closely and forces them ahead. Each carrier is addressed by means of a label for its destined station. Trains are despatched around the circuits at stated times, usually at fifteen-minute intervals. As they arrive at the various stations, carriers are taken out and others put in, and the trains sent on their way. The carriers consist of iron cylinders, closed at one end, with a leather case that slides over them and closes the open end. They weigh, when filled with thirty-five messages, twelve and one-half ounces, and they will travel about twelve hundred miles before the leather cover is so worn that it must be thrown away. The pistons are made of a wooden cone, covered with iron, and having a “cup-leather” upon the rear end that fits the tube closely. The sending and receiving apparatus consists of sections of tube closed at one end, having a door on the side, through which carriers are inserted or despatched. A peculiar form of fork is used