638 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



From these considerations, it may readily be seen that the 

 cylinders and piston need not be so large as in the steam system ; 

 for as steam attenuates in the passage from the boiler, and under 

 the moving piston, and although it has not time in a locomotive 

 to lose much heat and condense, it has but a limited expansion 

 when discharged from the boiler — certainly very inferior to the 

 expansion of compressed air, which will always be augmented 

 by the increased temperature of the cylinder from the friction of 

 the piston above the natural temperature of the reservoir. 

 Smaller cylinders will therefore be necessary to economize 

 power; and as the pressures on the piston can be increased or 

 decreased to the maximum or minimum resistance occasionally 

 demanded on inclines, or the various loads to be drawn, the ex- 

 penditure of power and the duty of a line may thus be readily 

 equalized. 



I have thus dwelt at some length upon the single objection 

 advanced here ; because, if that objection be of any weight, we 

 need not proceed another step ; it would be fatal to any attempt 

 to introduce compressed air as a motive power on railways. And 

 I have shown, by reference to the authority of enlightened engi- 

 neers, that, as to the cylinder, smaller cylinders than for steam 

 are demanded for the economical use of the power ; • and that the 

 power itself is eminently adapted to its being worked expansively. 

 And I have given the reasons — if not all that might be adduced, 

 as many as time will allow me even to refer to — on which these 

 conclusions are founded. 



There is therefore no practical difficulty to be overcome, 

 growing out of the rapid expenditure of the power of compressed 

 air, which requires a larger cylinder than for steam ; and none 

 whatever on the score of expansion, because the power, as we 

 have seen, is peculiarly adapted to that method of working, and 

 therefore every advantage of the principle of expansion may be 

 embraced in it. 



But a suggestion was also made here at the same time, to the 

 eflfect that, with a full charged receiver, if compressed in what- 

 ever density of the capacity of 65 cubic feet, which I had stated 

 to be the contents of that proposed, an ordinary car could not 

 be propelled a single mile by reason of this supposed rapid expen- 

 diture of the medium. It will be a sufficient answer to that sug- 

 gestion to advert at once to the result of practical experiments 

 made by both of the distinguished individuals already mentioned. 



