292 nvDHArur CKAXK 



from a pound of carbon in powder, was fourteen times as 

 much as the Watt engine gave from a pound of coal. 



" ME. GlDDY, " LONDON, No. 42, ST. MARY AXE, June 18th, 1828. 



" Sir, A few days since a Mr. Linthorn called on me 

 and requested me to accompany him to Cable Street, near the 

 Brunswick Theatre, to see a crane worked by the atmosphere, 

 in a double-acting engine attached to it. He has a patent, and 

 has entered into a contract with the St. Katharine's Dock Com- 

 pany to work their cranes, 140 in number, by a steam-engine 

 of sufficient power to command the whole of them, by placing 

 air-pipes around the docks, with a branch to each crane. To 

 each crane is fixed a 10-inch cylinder, 20-inch stroke, double- 

 acting. The atmosphere pressing on the piston like steam, the 

 air is drawn from the pipes by a large air-pump and steam-engine. 



" On being requested to give my opinion on this plan, after 

 seeing one crane worked, I informed them of the disappoint- 

 ment that the ironmaster, Mr. Wilkinson, in Shropshire, several 

 years since experienced, on the resistance of air in passing through 

 long pipes from his blast-engine to his furnaces. He said he 

 was aware of that circumstance, and it had since been further 

 proved in London by one of the gas companies attempting to 

 force gas a considerable distance, and who also failed. 



" He thought that forcing an elastic fluid, and drawing it by 

 a vacuum, were very different things, and that the error was 

 removed by drawing in place of forcing. For my part I am not 

 convinced on this head ; but am still of opinion that the result 

 on trial will be found nearly the same. However, let that be as 

 it may, the expense and complication of the machine, having 

 a double engine, with its gear attached to every separate crane, 

 together with the immense quantity of air thrown into the air- 

 pump from 140 double engines of 10 inches diameter, 20-inch 

 stroke, eighty strokes per minute, and considering the numerous 

 air leaks in such an extent of pipes and machines, must reduce 

 the effect of the pressure of the atmosphere on each piston to a 

 comparatively small power, unless the air-pump and steam- 

 engine are beyond all reasonable bounds. 



"Those objections I made them acquainted with, and said 



