The London system of pneumatic dispatch differs from those of Continental cities just men tioned chiefly in being a radial system instead of a circuit system. The tubes radiate from a central power station to substations located at points. In 1897 the system comprised 42 stations and 31 miles of tubes. The first London tube was installed by Siemens Bros., in 1870. but the present lines have been greatly improved over the original construction. Other British cities which have systems of pneumatic dispatch are Liverpool, \IaWrhester• Birmingham, Glas gow, IliItin, and Newcastle. .Nlention should be the atmospheric railway built in Lon don in 1863, from Euston to a station in Ever shalt Street, 1800 feet. and extended in 1872 from Euston to the General Post-office, 14•°_04 feet. The original tunnel was a single tunnel flat on the bottom and 1)-shaped in section feet high and feet wide. The carriers were cradle-like boxes fitting the tunnel and they were moved at a speed of 17 miles per hour. The second line built was a double tunnel line each 4 feet high and feel wide. These atmospheric railways were used to carry the mails for a lime, but were found to be slow and expensive and were aban doned.
1893 the 'United States Yost•ot]ice Department in stalled pneumatic dispatch between its main post-office and its substation at the Bourse, Phila delphia. This line is 2974 feet long, with tubes eight inches in diameter, and the carriers travel at a speed of about •'5 miles per hour. Thi, sys tem has since been extended to reach the ter minal stations of the Pennsylvania and the Phila delphia and Reading railways. In 1897-98 there were installed 6.83 miles of pneumatic dispatch connecting the general post-office in New York City with the Brooklyn post-office, the Grand Central Station, and intermediate substations. As the result of the experience with these lines. Congress, by an act dated June 2, 1900, ordered a committee of experts to be appointed to investi gate and report upon the cost, construction, and utility of such systems for these and other large cities. This committee investigated these ques tions for eleven large cities and submitted a voluminous report in 1901.
The Batehil•ller system, which was first installed at New York and Philadelphia, on the lines in use in 1901, employed compressed air at a pres sure of from five to ten pounds. The compressed air may be furnished by any improved type of air compressor or high-pressure blower and forces the carriage through a cast-iron pipe which is bored true and smooth and carefully jointed. The tubes, which are six and eight inches in di ameter, are laid in a double line to facilitate Perhaps the first attempt at pneumatic dis patch in America was made by A. E. Beach. who invented and exhibited a full-size working model of an atmospheric railway in 1867. Some years later Mr. Beach began the construction of an atmospheric railway tunnel under Broadway, New York City, and had completed a short dis tance of tunnel when the work was abandoned.
In his working model Mr. Beach used a tube six feet in diameter through which a ear seating ten persons was propelled by air pressure generated by a fan. This is the only attempt actually made in America at atmospheric railway con struction. The use of pneumatic dispatch has, however, became quite extended. Perhaps the most extensive use is of small pneumatic tubes in stores for dispatching each to and from a cen trally located cashier's desk. Seamless brass tithing is generally used and the power is sup plied by rotary blowers. The Western 'Union Telegraph Company has pneumatic dispatch sys tems in use in New York and Chicago. and simi lar private systems are in use elsewhere. In traffic in opposite directions. The carriers are symmetrical in form, of the shape shown in the illustration, and of a diameter about one inch less than that of the tube. A door in the end of each carrier gives access to the interior. They are from 16 to 30 inches in length and weigh from 7 to 10 pounds. Near each end are placed packing rings of cotton fabric secured to the main hody by metal collars so as to insure a close fit in the tube. These packing rings are liffiricatediby vaseline. which makes easy running possible. The sending and receiving apparatus, which is located at each end and also at inter mediate stations on the line, is shown in the il lustration. In the sending apparatus two sec tions of the tube are supported in a swinging frame so that either can be brought into line with the main tube, through which there is a constant current of air. After a carrier has been placed in an iron trough it passes into an open tube section and is then swung into position so that it is in line with the main tube and the carrier is swept along by the pressure. The car Tier: usually have a headway of from five to fifteen seconds each, and may be dispatched auto matically. There are various forms of receivers, the use of which depends upon various conditions of atmospheric pressure. The action of the re ceiving apparatus is automatic, and as soon as a carrier arrives in the receiving chamber the Tatter is tilted and the carrier is discharged and the receiving chamber returned to its normal horizontal position. Automatic apparatus is also employed at the intermediate stations and the carriers designed for a particular station are turned aside from the main line tube. The use of pneumatic apparatus is constantly increas ing and there are cities in the United States in which it is being installed for the transmission of small packages.
to discharge a quantity of high explosive. The most successful pneumatic gun, the invention of Capt. E. L. Zalinski, U.S.A., is designed to dis charge projectiles loaded with a high explosive, such as dynamite, the shock of the discharge be ing kept low by the use of air. Pneumatic guns have not been taken up by governments, because it is felt that the problem of projecting a mass containing high explosives is not thoroughly solved by such means. See Ala GUN; ORD NANCE.