PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 589 



Mr. Butler. — It would be necessary to have a variable cut-ofF; 

 but I do not see how, in running four miles, with a proper supply 

 for the first two miles, even a variable cut-ofF could bring up the 

 speed for the last mile. It would be very much like getting up 

 steam in your boilers, and then putting your fire out. 



Mr. Fisher. — How nearly new is this general idea? 



Mr. Haskins. — It is not new. Carriages have been run ten or 

 fifteen years ago ; but they had no mode of replenishing the 

 power. 



Mr. Stetson was confident from some careful calculations that 

 the advantages of compressed air for a motive power had been 

 generally underrated by mechanics ; and that air could be suffi- 

 ciently compressed to run a car four miles or more. The difiicul- 

 ties could be overcome, by passing the air through a small open- 

 ing, so as to produce only the requisite pressure, or in some other 

 way to be invented. The varying of the cut-off need not com- 

 mence until we get near the end of the journey. 



Mr. Fisher said that compressed air had been experimented 

 with for sixty years. There would be various economies in its 

 use upon railroads, such as the use of inferior fuel, or of water 

 power at the stations, the saving of loss while the locomotive is 

 waiting, and the dispensing with the firemen. For a line through 

 Broadway, five miles in length, the experiment was worthy of 

 trial. He had computed that a carriage could be driven five 

 miles over a common road with a single charge of air. 



The President^ said the time must come when the space over 

 the sidewalk will be devoted to carrying passengers in some of 

 the most important streets and avenues of this city. For this 

 elevated track horses could not be used ; and if any man could 

 devise a substitute, so that horses could be taken from our streets 

 entirely, he would be a public benefactor. 



Subject selected for the next meeting is " The mechanical and 

 chemical properties of cotton, and substitutes therefor," proposed 

 by Mr. Stetson. Adjourned. 



American Institute, Polytechnic Association, ) 

 February 21, 1861. S 



Professor Mason in the chair. 



Mr. Johnson proposed the subject of Soluble Quartz for future 

 consideration. 



