PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 377 



gas generated by the burning' fuel. Several substitutes had been pro- 

 posed — such as springs, compressed air, iiot water for making steam to be 

 used on sliort routes. 



It was stated that the great(.'st power yet obtained from a spring would 

 not raise its own weigiit higher than sixty feet. 



The Chairman desired to direct attention to the question now before the 

 meeting. Tiie average pressure derived fVoni a partial exhaustion of the 

 air in the tiiiuiel is said to be two and a half ounces per sijuare inch ; the 

 exact size of the tunnol is not given in the articles read, but supposing it 

 to be ten feet iiigli and ten widi', the area of the car and the surrounding 

 ring, which is virtually a piston, would be one hundred square feet. A 

 pressure of two ounces and a half on the inch would Do about twenty-two 

 pounds per s(juare foot, or two thousand two hundred pounds fur the total 

 pressure on tiio piston. To obtain this pressure the whole cohuiiu of air in 

 the tiinnel is partially raritied by means of a fan, which is not as economi- 

 cal as an air-pump having a reciprocating piston. The length of the tun- 

 nel is 1,800 foet, and the bulU of air within it is equal to 180,000 cubic 

 feet; just in proportion to amount of air pumped out is the pressure on the 

 car. The removal of half the air in the tunnel before the car is started 

 would give it a pressure of seven and a half pounds per square inch ; this 

 wujuld be about fifty times more than is said to be required for moving a 

 single car. The pumping must be continued during the passage of the car, 

 because it is constantly pressing the remaining air into a smaller space. 

 If we take into consideration tlie friction of the air pump and of the whole 

 column of air moving in the tunnel, as well as the friction and leakage of 

 the car piston, it would appear that the proposed plan is far more expen- 

 sive than the ordinary method of railway locoiuotion. The mode of pack- 

 ing the piston, by means of bristles, is doubtless quite effective where the 

 pressure per square inch is so small. 



Dr. D. D. Parmelee said the ball of the air-gun used in shooting galleries 

 is ptacked by a (ibrous appendage against which the air acts. 



Dr. W. Rowell alluded to an article in the London Mechanics' Magazine, 

 which states that the plan of locomotion now under discussion was pro- 

 posed fifty-four 3'ears ago. 



Mr. J. B. Hoot said he had made some calculations from the data given 

 and found that the power required is far greater than by the ordinary loco- 

 motive. The friction becomes a very serious objection when the tunnel is 

 several miles in length. Indeed, it may be safely averred that more than 

 five times the usual power would be used in this new method of propulsion, 



Mr. Fisher estimated the weight of the air to be removed in a tunnel one 

 mile long, at 44,000 pounds, the whole of which must pass through the fan 

 or pvjmj) before tlie car reaches its destination. 



The Chairman added that where the power of stationary steam engines 

 had beerr applied, in the most economical way, to moving cars, the practice 

 was finally abandoned. Formerly the Albany and Schenectady Kailway 

 had an inclined plane at each end, one leading to the valley of the Hudson 

 Kiver, and the other to the valley of the Mohawk. Cars were drawn up by 

 means of a stationary engine at the top of eacii plane. After years of trial^ 



