744 Transactions of tee American Institute. 



two years, -would, in my estimation, be folly. The cost of tlic right 

 of eminent domain and the purchase of necessary lands, it is impos- 

 sible to estimate till after the survey and contracts are made; but I 

 think it entirely safe to say that the cost of all recited rights, running 

 stock and complete equipments, will not exceed nine times that of 

 the excavation. If so, it will bring the work at less than $775,000 

 per mile. 



At each intermediate single shaft, after the removal of the excavated 

 material is completed, I propose to erect a stack or chimney to a proi)er 

 height with appliance at the top to secure a constant draft from the 

 tunnel. This, with the constant ingress of fresh air at the stations, 

 and the movements back and forth of the cars, will secure a good, 

 wholesome ventilation, even if we use dummy, or smoke-consuming 

 engines. But, instead of steam engines of any kind in the tunnel, I 

 propose to use pressed air engines. The steam engines at the several 

 stations besides working the elevators, may be employed in com- 

 pressing air, by means of some of the lately improved air presses, one 

 of whiiih was shown us here at a late meeting. The pressed air 

 receiver, or magazine for each car, may consist of eight or ten iron 

 tubes, say six or eight inches diameter, extending beneath the car, its 

 whole length, so connected as to make them a common reservoir. 

 This, with a pressure of say twenty to thirty atmospheres, will contain 

 force enough to propel the car rapidly two miles or more. Further- 

 more, when the valve is closed for stopping the car, the force which 

 has bjon converted into momentum in the car, and its contents is 

 now exerted upon the engine by a reverse action, in pumping and 

 refilling the reservoir, and the resistance of such action helps to serve 

 the purpose of a break in stopping the car. 



In this arrangement there is remarkable economy in the conserva- 

 tion of force. 



The magazines at the several stations should be composed of a 

 large number of pipes or small cylinders, capable of sustaining great 

 pressure, and connected by a common pipe running tlirough the tun- 

 nel from end to end, which will convert them all into one great and 

 general reservoir, to be provided with suitable check-valves, so that 

 in case of sudden and rapid exhaustion on account of accident of 

 any kind, the accumulated pressure may be sa^•ed from general and 

 entire loss. 



The magazine of any car may be replenished to full force from the 

 general reservoir at any station in ten or fifteen seconds, and with 

 great facility. 



