A. B. Quinhi/ on Cmnfc Motioru 321 



koownj has no connexion with a loss of power in the steam- 

 engine. 



With a view to clearness, and fpr the information of the 

 writer of the article in the North American Review,'! shall 

 here give a definition of the power of a steam-engine. The 

 power of a steam-engine is the product of the elastic force of 

 the steam employed and the surface of the piston upon which 

 it acts. 



This definition being admitted, it is easy to perceive that 

 both the writers who have made the estimates, have com- 

 mitted not only '' a very great," but a very egregious, blun- 

 der, since they both have taken, not the elastic force of the 

 steam employed, and the surface of the piston upon which it 

 acts, but the quantity of coal consumed, for the measure of 

 the power of the respective engiiies. 



Besides this blunder, it is further to be noticed, that both 

 the writers in question have founded their inference on the 

 presumption that the engines employed in drawing the matter 

 out of the mines, are always uniformly and sufficiently loaded. 

 But on this subject they have stated no evidence, or have re- 

 ferred to no authority ; and it is more than probable that, iii 

 raising the matter out of the mines, the load applied in the 

 buckets was neither uniform nor sufficient; and consequently 

 "a blunder'' has, on this score^, been committed, as well as 

 in making the quantity of coal consumed to be the measure 

 of the power of the respective engines. 



I shall now notice the words, " As appears from the re- 

 ports on the performance of the engines used at the mines in 

 Cornwall.'' 



On the subject of this assertion, I shall take the liberty to 

 state that there is not in the Messrs. Leans' reports one word 

 that justifies, or even makes admissible, the assertion that, 

 " there is in the steam-engine a loss of power m changing the 

 direction of its action from rectilinear to rotary by the wc- 

 thods in common, practice.'^ 



In Tilloch's Philosophical Magazine we have the whole 

 series of reports on the performance of the engines used at 

 the mines in Cornwall, by Messrs. T. St J. Lean, com- 

 mencing Aug. 1811, and ending Nov. 1818 5 and in these 

 reports the case noticed by the writer of the article Steam 

 Engine, Rees' Cyclopaedia, is not mentioned ; and if it was 

 mentioned it would never lead a scientific writer, who is com- 

 petently acquainted with the steam-engine and with the 



VcL, IX.— No, ^, 4> 



