642 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



■which the gratifying performance of his engine was thus success- 

 fully accomplished, embodying the description in remarks, which 

 may tend, in his own words, "to a better understanding of the 

 improvements in locomotion," and to which, from their remark- 

 able pertinency, I beg leave to invite your attention. 



" The practicability of the use of compressed air, solely depends 

 on the means of controlling it at high densities, and of regulating 

 and producing a uniform and continuous working pressure. 



" A compressed air locomotive is charged with an amount of 

 power previously prepared for a given distance and not genera- 

 ted as in a steamer while running ; consequently, so great an 

 amount of power being packed up in so small a compass as an 

 ordinary railway carriage, designed for the proper accommoda- 

 tion of the usual number of passengers would aiford, the pressure 

 in the receiver, which must be much greater than high pressure 

 steam, will require skillful control ; and as this packed up power 

 has to be expended according to the friction or resistance of the 

 engine, and the load it has to draw, it will be manifest that a 

 certain and perfect means of fixing, maintaining and adjusting 

 the working pressure on the piston, is of the most material con- 

 sequence in the working of them. 



"In a steamer it is necessary that the evaporating power of 

 the engine should be able to generate sufficient steam, at a pres- 

 sure in the boiler fully equal to the resistance of the engine and 

 its load on the pistons ; and it is the part of a skillful driver so 

 to urge his fire as to continue this condition, according to the 

 duty required of his engine. 



" But, in compressed air engines, this skill and vigilant atten- 

 tion to the generation of the power will not be required, as com- 

 pressed air will be prepared for him at certain stations, where he 

 will replenish his engine with air, as he does now with water, to 

 carry him on to another replenishing station. Taking up from 

 stationary reservoirs, in two or three minutes the amount of 

 power that will carry him over, say 20 or 30 miles, his business 

 will be simply to apply to the piston, by means of the regulator, 

 a pressure that shall overcome the resistance, and to regulate 

 the supply to the driving cylinders, so as to effect the requisite 



" All the steam generated in the boilers does not pass through 

 the cylinders, as all the pressure indicated in the boiler above 

 the pressure that overcomes the resistance of the pistons is lost 



