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XL VI . On a New Rotative Steam-Engine. By John Taylor, 

 Esq., F.H.S., Treas. G.S., <$•<?. 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 

 IT is very well known to those who have observed the duty 

 ■*■ of steam-engines employed in the mines of Cornwall, that 

 an enormous difference has existed between those which raise 

 water by a reciprocating motion, and those which for other 

 purposes have that motion converted into a rotative one by 

 the intervention of a crank. The cause of this difference has 

 often been speculated upon, but has not, I believe, been well 

 explained : it is important in an ceconomical point of view, as 

 while in the pumping engines 60 millions pounds are com- 

 monly raised one foot by each bushel of coal consumed, the 

 rotative engines for stamping ores have seldom raised more 

 than 20 millions; and those for winding up the ores from un- 

 derground are found to be even far below this in effect. 



Now, it should be observed that the pumping-engines are 

 at present universally, I believe, single engines, that is to say, 

 receiving the steam from the boiler on one side of the piston 

 only, the principle of working double, as it is called, which was 

 introduced by Mr. Watt, having been for some time discarded; 

 and in these single engines the method of working high pres- 

 sure steam expansively, which we owe to Mr. Woolf, has long 

 been used with the greatest advantage. 



The rotative engines in Cornwall, like all others which are 

 used for manufacturing purposes, are double engines, and re- 

 ceive the steam alternately above and below the piston ; and 

 though attempts have been made to work them expansively, 

 these attempts have not been very successful. 



The object of my present address to you is to notice an 

 engine which has lately been constructed for a mine in which 

 I am interested, which is a rotative one for stamping tin ores, 

 and which when I visited the mine a few days since was cal- 

 culated to be performing a duty of about 60 millions, or nearly 

 equal to the average of the better class of reciprocating en- 

 gines, and nearly three times as much as the best rotative en- 

 gines have hitherto done. 



I wish to call the attention of persons concerned in the use 

 of steam-engines to this fact, because if it should be found 

 that this rate of duty can be maintained, a very great im- 

 provement may take place in all such as are most generally 

 employed. 



Third Series. Vol. 7. No. 41. Nov. 1835. 3 B 



