1IYPUAULIC CRANE. 293 



tli.it, before they went to sucli an expense, it would be a safer 

 plan to first make further inquiry, so that their first experiment 

 might be on a sure plan, for the other dock companies were 

 looking for the results of this experiment. 



" At the time I was informed of this plan, a thought struck 

 me that it might be accomplished by another mode preferable 

 to this: by a steam-engine to force water in pipes round the 

 dock, to say 30 or 40 Ibs. to the inch, more or less, and to have 

 a worm-shaft, working in a worm-wheel, the same as a common 

 roasting-jack, and apply to the worm-shaft a spouting arm like 

 Barker's mill; the worm-shaft standing perpendicular would 

 work the worm-wheel fixed in the chain-barrel shaft of the crane. 



" This would make a very simple and cheap machine, and 

 produce a circular motion at once, instead of a piston alternating 

 motion to drive a rotary motion. My report had some weight 

 with them ; inquiry is to be made into the plan proposed by 

 me, so as to remunerate me, provided my plan is considered 

 good. Mr. Linthorn wishes an investigation before scientific 

 and able judges, and requested me to name some one. I must 

 again make free in asking the favour of your advice (which you 

 have so ably given me for thirty years) on this plan. Mr. Lin- 

 thorn intends to request Dr. Wollaston to accompany you, any 

 day convenient to you. In the meantime, should, you see him, 

 it might not be amiss to mention it to him ; and should you be 

 able to attend for an hour or two to this business, I would thank 

 you to drop me a note, saying when it may be convenient. 

 There is a memorandum of an agreement between Mr. Linthorn 

 and me ; but the plan 1 suggest is only at present made public 

 to him and yourself. 



" Your most obedient servant, 



" RICHARD TREVITIIIOK." 



The reduction of friction by the use of an. air- vacuum 

 engine for working cranes, as designed by Mr. Linthorn, 

 in lieu of an air-pressure engine, was doubted by Trevi- 

 thick. 



The Mont Cenis pneumatic-pressure machines which 

 ^ writer saw at work lost much power by friction 

 VOL. n. x 



