294 ICE MACHINE. 



before experience had taught remedies. The pneumatic 

 vacuum tubes which propelled the trains on the South 

 Devon Railway, failed to give the power that was 

 expected. Sir William Armstrong's hydraulic cranes, 

 brought into use not many years after the date of Trevi- 

 thick's letter, have been found effective. The writer, not 

 knowing that Trevithick had before recommended hy- 

 draulic cranes for warehouses, accompanied Sir William 

 over his works, then being erected near Newcastle-on- 

 Tyne, and talked with him on the detail of his crane 

 designs. 



Trevithick thought of giving circular motion to the 

 crane chain-barrel by the attachment of a screw- 

 propeller, acted on by the force of a current of water 

 at a pressure of 30 or 40 Ibs. to the inch. Sir William 

 Armstrong's arrangement was quite different ; the merit 

 due to Trevithick was for having pointed out the 

 suitability of water as a means of conveying power 

 through warehouses where fire was inadmissible. 



" ME. GILBERT, "LONDON, 42, ST. MARY AXE, June 29th, 1828. 



" Sir, Fancy and whim still prompt me to trouble you, 

 and perhaps may continue to do until I exhaust your patience. 

 A few days since I was in company where a person said that 

 100,0007. a year was paid for ice, the greatest part of which 

 was brought by ships sent on purpose to the Greenland seas. 

 A thought struck me at the moment that artificial cold might 

 be made very cheap by the power of steam-jengines ; by com- 

 pressing air in a condenser surrounded by water, and an injection 

 to the same, so as to instantly cool down the highly-compressed 

 air to the temperature of the surrounding air, and then admitting 

 it to escape into liquid. This would reduce the temperature to 

 any state of cold required. 



" I remain, Sir, 



" Your very humble servant, 



" RICHARD TREVITHIQK." 



