42 ANNUAL OF SCIENTIFIC DISCOVERY. 



nication within the metropolis and other large towns, or wherever tun- 

 nelled lines with steep gradients exist. The chief obstacles encountered 

 in practically working the atmospheric railway, introduced some 15 

 years ago, are considered to have been effectually overcome by the pres- 

 ent modification of the principle. Under the former system the tube was 

 of very small size, and lixed upon the ground ; a longitudinal or contin- 

 uous valve opening at the top, along which a rod, connecting the piston 

 with the carriages passed, and the valve closing behind the rod as it 

 moved onwards. The amount of atmospheric pressure required to be 

 exerted where the area of the tube was so small was enormous, being 

 from seven to ten pounds per square inch ; whereas under the present 

 system the pressure is only two and one half ounces per square inch ; 

 and, moreover, the great leakage and waste of power whichrendered the 

 old atmosphere system so costly in working are here in great measure 

 avoided. It need hardly be added that the worst drawbacks to traveling 

 through tunnels viz : the smoke and sulphureous vapors emitted from 

 the locomotive, and the close, unwholesome atmosphere of the tunnels 

 themselves are in this case got rid of. Every train, in fact, carries its 

 own supply of fresh air along with it, and also expels the foul air before it. 



Improved Pneumatic Despatch. Mr. C. A. Varley, of Liverpool, 

 has invented an improved apparatus for the transmission of parcels on 

 the pneumatic principle. The novelty of the invention consists in the 

 use of compressed air as a motive power for the propulsion of car- 

 riages in one direction, while a vacuum is created for their transmission 

 in the other. In the old plan, the pressure used was limited to that 

 of the atmosphere, 15 pounds to the square inch, but by the new 

 system, any amount of pressure can be obtained by the use of com- 

 pressed air. 



The London Engineer thus describes the application of Mr. Varley's 

 invention by one of the telegraph companies in Liverpool, for the trans- 

 mission of written despatches from one office to another, a distance 

 of about 300 yards. It says : "In the cells beneath the central office 

 of the company in Castle Street, is an engine usually worked at about 

 one horse-power, though much more force can be gained if necessary. 

 This engine works a double air-pump, which removes the air from one 

 chamber and forces it into another. The chambers are called the ' ex- 

 h uist ' and the ' compressed air ' chambers, and are connected by pipes 

 and valves with the apparatus in the room on the first floor. If a mes- 

 sage has to be sent, it is placed in a little round flannel bag made to 

 tit loosely into the tube. A valve is then opened in connection witU 

 the compressed air clnmber; the compressed air, which is kept at 11 

 pounds on the square inch, rushes into the tube, and the bag is urged 

 with immense rapidity to its destination. On its arrival there the sig- 

 nal is given on an electric bell, the valve stopped, and the operator is 

 ready to receive the return message. The signal is given on the elec- 

 tric bell, and the valve and all outer communications at the operator's 

 end closed. A communication is then opened with the exhaust cham- 

 ber, and the air, rushing from the far end to supply the vacuum, brings 

 the little bag along with it. On its arrival a spring is touched, the 

 valve fills, and the air rushes in. The operator is then able to open 

 the case and take out the message. The average speed of these tubes, 

 which are one and one half inches diameter, is about 40 miles per 



