448 ANNUAL EECORD OF SCIENCE AND INDUSTRY. 



The memoir is accompanied by extensive tables to facilitate 

 the solution of the problems arising in pneumatic transmis- 

 sion. Minutes of the Proceedings of the Institution of Civil 

 Engineers^ London^ 1876, 53. 



PXEUMATIC TUBES IN PAKIS. 



In a memoir by C. Bontemps on the movement of air in 

 pneumatic tubes, a very complete account is given of the 

 system of pneumatic transmission as at present existing in 

 Paris. He states that when an obstruction exists any where 

 in the underground tubes, its location is determined by firing 

 a pistol into the tube ; the resulting wave of compressed air, 

 traversing the tube at the rate of a thousand feet a second, 

 strikes the obstruction, and is then reflected back to its ori- 

 gin, where it strikes against a delicate diaphragm, and its 

 arrival is recorded electrically upon a very sensitive chrono- 

 graph, on which also the instant of firing the pistol had been 

 previously recorded. The wave of sound on reaching the 

 diaphragm is recorded, and thence reflected back, and a sec- 

 ond time strikes the obstacle, and returns to the diaphragm. 

 This operation is several times repeated, so that several suc- 

 cessive measurements can be made of the time required by 

 the sound-wave to traverse to and fro within the pneumatic 

 tube. 31iniites of the Proceedings of the Institution of Civil 

 Engineers^ London^ 1876, 105. 



PRIXCIPLES OF THE COXSTRUCTIOX OF ^VVIIEELS. 



In an essay on the construction of wheels and axle-trees. 

 Captain Kemmis, of the Royal Artillery, states that the most 

 severe test to which spokes are subject is from the lateral 

 thrust brought to bear upon the nave when one wheel be- 

 comes lower than the other by dipping into a rut. In order, 

 therefore, to place them in a better position to resist this 

 thrust the wheel is dished, or formed into a kind of dome, 

 and just as the dome or arch is strong from its form to resist 

 pressure upon the crown, tending to crush it in, so is the 

 wheel made strong by the dish to resist the lateral thrust 

 tending to throw the nave outward. In fact, not only do 

 the spokes, sustained by the tire, give mutual support to 

 each other, but the lateral thrust upon each becomes partly 

 converted into a compressing strain which the wood has bet- 



