588 TRANSACTIONS OF THE AMERICAN INSTITUTE, 



and indirect power of the two mediums — steam and atmospheric 

 pressure — a careful investigation, not- only into the administra- 

 tive department, but into that also of construction for either 

 system, will indicate the favorable consideration which is due to 

 that of compressed air. 



Suffice it to say that, by the compression of the atmosphere, 

 we obtain one of the most potent, if not the best, of the known 

 powers for the propulsion of cars on a railway. In effective pro- 

 pelling force, compressed air is, comparing densities, the full 

 equivalent of steam. While it dispenses with much of the 

 machinery and construction incidental to steam as a power on 

 the track, with superadded cost and weight, it involves no com- 

 plications that make it difficult to the comprehension of a child 

 of ordinary capacity and intelligence practically to understand 

 and apply. It is also relatively free from danger — not compara- 

 tivelyj alone, but superlatively safe — and for the service of the 

 rail track, in an economic and in every other point of view, it is 

 not the competitor alone of steam, but its superior. 



On the 26th of November last I submitted to the World, and 

 had published in that journal, a proposition to introduce com- 

 pressed air as a motive power for a railway to be constructed in 

 Broadway, called the overhead railroad, to occupy the space on 

 either side of the street, 16 feet above the sidewalk. The struc- 

 ture to be an ornamental terrace or balcony of iron, projecting 

 from the buildings, covering the entire walk, and even extending 

 two and a half or three feet beyond it into the street, supported 

 on one side by wrought iron columns placed in a line with the 

 present lamp posts. 



The plan of the structure was projected by Mr. John B. Wick- 

 ersham, in 1854, and was much noticed at the time and favor- 

 ably spoken of by the press and by property owners in Broad- 

 way, though Mr. Wickersham proposed to propel his cars by 

 horse power. In my article, I undertook to show that the use of 

 horses in such a position would be inexpedient, if not practically 

 impossible. The plan there proposed is one that is worth con- 

 sidering. 



Mr. Dibben. — As soon as the pressure falls below 60 lbs. you 

 must increase the size of the cylinder or change your gearing, or 

 your speed will be reduced. To carry a car a mile, you would 

 need about 1,000 cubic feet of air at 60 or 80 lbs. pressure to be 

 kept up to that pressure. 



