Page:The American Cyclopædia (1879) Volume XIII.djvu/647

 PNEUMATIC DESPATCH PNEUMATIC RAILWAY 627 minute. By means of an improvement in- vented by Messrs. Siemens and Halske, while a current of air circulates through any number of stations, a carriage may be introduced or stopped at any intermediate station. In Paris a system of pneumatic transmission was de- cided upon in 1865, and an experimental line was laid between the place de la Bourse and the Grand Hotel (boulevard des Capucines) in 1866. It was found by experiments that the water of the town could be used to produce, by being forced into reservoirs, or allowed to run from them, alternate compression and ex- pansion of air in connecting reservoirs, the action being changed at will by a system of cocks ; and this was the mode adopted for the propulsion of packages through the tubes. Since then a complete and comprehensive system has been carried out from time to time, the motive power in many of the recent extensions, however, being steam. In 1874 the station in the place du Havre was con- nected with the one at the Grand Hotel, and the water at this station was employed to produce pressure and vacuum for working in both directions. There are now (1875) 45 stations in the city, and the number of des- patches of all kinds transmitted is about 25,000 a month, or an average of 830 a day, of which the Bourse station sends over 2,500. A pneu- matic despatch system is now (July, 1875) in operation in the Western Union telegraph building at the corner of Broadway and Dey street, New York. The moving of the pack- ages is done by exhausting, accomplished by a Root's rotary blower. Packages are sent from all parts of the building to the oper- ating room in the seventh story, but most of them from the receiving room on the ground floor. In the centre of the operating room stands a chest about 5 ft. high, 18 in. wide, and about 12 ft. long. The upper part of it, about 6 in. deep, forms one chamber, connect- ing by openings, which may be closed or shut at pleasure, with a dozen or more chambers beneath. A large exhaust .pipe about 8 in. in diameter descends from the middle of the up- per chamber to the exhausting engine in the basement. From each receiving desk in the room below a tube about H in. in diameter descends to the floor, and then bending in a gradual curve is carried to the centre of the building, where it ascends vertically with its two dozen fellows to the chest in the operating room. Each compartment in the chest receives two tubes. A cylindrical box about 6 in. long and li in. in diameter, made of stout leather and open at one end, with a flange at one or both ends, as may be preferred, so as nearly to fit the tube, is used as the carrier for the light paper parcel, which is rolled up and held to its place inside the box by its elasticity. The weight of the whole load is but a few ounces, and consequently it needs a propelling force of less than half a pound to the square inch to force it up the tube with considerable ve- locity. At the orifice in the chamber of the exhausting chest is a bent spring, which ar- rests the box at its exit, so that it falls with little force in the chamber, at the same time that a lever is moved which closes a galvanic circuit, by which means an alarm is rung to call a messenger. PNEUMATIC RAILWAY. Since the plan of Medhurst mentioned in the preceding article, it has been sought to connect a passenger carriage with a pneumatic tube so as to afford a practical method of transit, and many patents have been taken out. The plan of Clegg and Samuda, patented in England in 1838, was one of the first invented, and is still as good as any since proposed. It was adopted on the atmospheric railways of Kingstown in Ireland, Croydon in England, and St. Germain in France. Along the upper side of the pneumatic tube there was a slit running throughout its entire length. Over this slit was placed a strip of flexible leather fastened hinge-like on one side. Be- neath the continuous leather strip there were short pieces of iron plating placed end to end, which just fitted into the slit, and on the upper side were plates of iron, somewhat wider than the slit. A knee-shaped piece of iron con- nected with the passenger carriage passed be- neath this continuous valve, and was attached to a cylinder several feet long, which acted as a piston, fitting the inside of the pneumatic tube by means of an India-rubber flange. The piston and pipe were lubricated with tallow. It was difficult to keep the apparatus in or- der, and notwithstanding that a speed of over 30 m. an hour was attained, the enterprise in this form has been abandoned. But it has been proposed in another form, which is essen- tially the same as that of the postal pneumatic despatch. In the summer of 1864 Mr. Ram- mell, 0. E., constructed a brickwork tunnel on the crystal palace grounds at Sydenham, Eng- land. The tunnel was about 10 ft. high by 9 ft. wide, and capable of admitting the largest carriage on the Great Western railway. Rails were laid upon the bottom of the tunnel, which was about 600 yards long. The route was laid with severe gradients and curves, to afford a practical test. A carriage capable of holding 30 passengers was provided with a flange of bristles at each end, by which it was made to fit the brickwork of the inside of the tunnel with such accuracy as to allow of the accumu- lation of sufficient pneumatic force to propel it. A small stationary steam engine worked a fan in the form of a hollow disk 22 ft. in diam- eter, so arranged as either to condense or rare- fy the air in the tunnel. It is thought that much of the objection against the old system of Clegg and Samuda has been overcome by Rammell's adoption of the pneumatic despatch system. In the old system the pressure re- quired within the pneumatic tube was from 8 to 10 Ibs. to the square inch, while when the tube receives the whole car a pressure of 2 or 3 oz. is all that is required to carry it over a