1036 Transactions of the American Institute. 



may be done instantly. Xor does lie state how long it will take to 

 change the passengers. On the London underground line it takes 

 forty-five seconds to change passengers ;_ and I believe they do it as 

 quickly as practicable. I think fifteen seconds will be required to lift 

 the car 10.5 feet and start it. Here then we have one minute for each 

 half mile, and one minute is left for running ; that is, to get an aver- 

 age speed of fifteen miles an hour, the mean speed while running 

 must be thirty miles an hour. To get a mean speed of thirty miles 

 an hour upon a half mile, there must be a much higher maxiniiun 

 speed. I am not now prepared to Calculate the acceleration 

 due to the cycloidal curve, half a mile long, which is here repre- 

 sented; but on a plane of this length and fall, the utmost speed 

 attainable by gravitation would be less than twenty-six feet per 

 second, if there were no resistance to rolling, and the mean speed 

 would be half, or thirteen feet per second, or less than nine miles an 

 hour. But the resistance to rolling, at fifteen miles an hour, eleven 

 pounds, per ton ; and at thirty miles it is sixteen pounds, on a solid 

 railway in good order. Upon a line with supports, each 250 feet 

 apart, as here proposed, there will be some flexure, whichwill increase 

 the resistance; but take the lowest figures, which give ^\^ as the resist- 

 ance. Now the ratio of the height to the length of the inclines is 

 ajr which leaves but a small margin for accidental resistance, such a& 

 wind, ice, etc. ; in fact, it would be unsafe to depend on so slight a 

 descent to give a speed of fifteen miles an hour if there were runs of 

 ten miles in length. A much greater height than 10.5 feet will be 

 required for such speed as will be economical for passengers — a height 

 so great that it will hardly be practicable above ground. 



The plan of Mr. P. W. Barlow, now being imperfectly applied by 

 his son, P. "VV. Barlow, Jr., in a " subway" under the Thames, would 

 be more feasible in New York, and would give a higher speed tlian 

 any other plan of railroad yet proposed ; in fact, it is the only plan 

 now economically practicable near Broadway ; the lots being so built 

 upon, that there is not enough room left for openings for a line worked 

 by locomotives. This plan, I think, will fail to give much speed 

 under the Thames, because the tunnel is so narrow that the atmos- 

 pheric resistance will be excessive ; but a tunnel as ample as that in 

 London might be made on the following plan : Each station to be 

 located in the middle of a block, on a level with the street nearly. 

 From the station the line could descend as steeply as practicable, say 

 one in eight, for a depth sufficient to give a high speed, say sixty 



