392 A1K-ELEVATOR. 



has been made by iron founders to deliver these castings on the 

 spot at 11. a ton ; at this rate the whole expense of completing 

 this national monument would not exceed 80,000/. 



"By a cylinder of 10 feet diameter, through which the public 

 would ascend to the top, bored and screwed together, in which a 

 hollow floating sheet-iron piston, with a seat round it, accommo- 

 dating 25 persons ; a steam-engine forces air into the cylinder- 

 column from a blast-cylinder of the same diameter and working 

 3 feet a second, would raise the floating piston to the top at the 

 same speed, or live or six minutes ascending the whole height; the 

 descent would require the same time. A door at the bottom of 

 the ascending cylinder opens inwards, which, when shut, could 

 not be opened again, having a pressure of 1500 Ibs. of air tending 

 to keep it shut until the piston descends to the bottom. By 

 closing the valve in the piston it would ascend to the top with 

 the passengers floating on air, the same as a regulating blast- 

 piston, or the upper plank of a smith's bellows. The air appa- 

 ratus from the engine should be of a proper size to admit the 

 floating piston with the passengers to rise and fall gradually, by 

 the partially opening or shutting of the valves in the top of the 

 piston. Supposing no springs or soft substance for the piston 

 to strike on at the bottom of the column-cylinder, descending 

 3 feet a second would give no greater shock than falling from 

 9 inches high, that being the rate of falling bodies, or the same 

 as a person being suddenly stopped when walking at the rate of 

 two miles an hour. The pressure of the air under the piston 

 would be about ^ Ib. on the square inch ; the aperture cannot 

 let the piston move above 3 feet a second, but this speed may 

 be reduced to any rate required by opening or shutting the 

 valves on the floating piston." 



To Trevithick's soaring genius nothing appeared 

 very small, or very large, or very costly ; not even the 

 cast-iron column 1000 feet high covered with gold. The 

 stone monument of London, 210 feet high, is admired 

 by many ; others climb into the cross on St. Paul's 

 Cathedral, 420 feet high; some make a long journey 

 to the great Pyramids, 500 feet high. How much 



