PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION, 587 



stationary steam power into a small tubular reservoir. This 

 reservoir will be laid along the track, between the rails, for the 

 transmission of the compressed fluid to the supplying stations. 



As an available motive power for the propulsion of cars on 

 railways, compressed air will be found to possess important 

 advantages over steam, of which, in positive effective force, it 

 is the exact equivalent, reckoning pound for pound. In the use 

 of compressed air, we derive all the effective force steam is capa- 

 ble of imparting at the same density ; while, with the one, we 

 may use with impunity a far greater pressure than would be safe 

 with the other. The reservoir and receiver for compressed air 

 may be charged up to two or even to five hundred pounds, if the 

 connecting apparatus be made capable of enduring the test, 

 without the risk of danger from explosion ; while, with steam, 

 we cannot safely use a greater pressure than fifty to seventy-five 

 pounds. Compressed air, at any density that would ever be re- 

 quisite for the propulsion of cars, is known to be free from the 

 hazards, by explosion, which so often result from the use of steam. 

 Hence the relative safety of the two agents, and the manifest 

 advantage to be derived from the use of a medium power, which, 

 at equal densities, is fully equal to that which in common use 

 and by common consent has obtained the character of being the 

 best. 



The application of compressed atmospheric air as a motive 

 power is based upon well-settled principles of mechanical science, 

 and needs no argument to establish its practical value. The 

 method proposed of employing the power, after making due 

 allowance for the loss by waste and that due to the process of 

 compression by friction, would reduce the cost of propulsion 

 greatly below that of the direct agency of steam; where the ex- 

 cessive waste of caloric by exposure to the atmosphere — to 

 which stationary steam engines for the compression of air are 

 not subjected in like degree — the increased cost of construction 

 rendered necessary to provide for the immense weight of loco- 

 motives, with tenders and material, involving a grievous daily 

 tax in the form of interest ; and the serious item which the wear 

 and tear of the road becomes under the grinding, crushing 

 gravity of the steam locomotive, are so many among a host 

 which might be adduced of formidable counterpoises ever at war 

 with the economical administration of a railway. 



On the score of economy, in the comparison between the direct 



