A. A. Quinby on Crank Motion. 319 



in diameter; but their performance, with respect to coal, is 

 only 3, 3f,.4, and 5 miUions. The best engine they have, 

 draws only from 9| to 1 1 million pounds, one foot high, with 

 each bushel of coal, which is only one-third of the perform- 

 ance. of the best large engine employed in pumping.'' 



"One of Woolf's double [cylinder] engines, at Wheal 

 Fortune mine, in May 1816, drew only three million pounds, 

 one foot high, with each bushel; but another, at Wheal Var 

 mine, drew six millions" 



Now it is deemed proper here to notice, first, that in the 

 case just quoted, the author (the writer of the article Steam 

 Engine, Rees'*Cyclopgedia) attributes all the difference be- 

 tween the performance of the two engines employed, to two 

 causes, viz. the application of the rotative motion by the 

 crank, and to the smallness of the engines; and, secondly, 

 that the writer of the article in the North American Review 

 offers this very case as the basis on which he founds his asser- 

 tion, that " There is, iq the steam-engine, a loss of power in 

 changing the direction of its action, from rectilinear to rotary, 

 by the methods in common practice.''^* 



With respect to the first of these opinions, it is to be re- 

 marked, that however respectable the writer of the article 

 Steam Engine, Rees' Cyclopaedia, may be, as a man of 

 science, his knowledge was inadequate to the subject on 

 which he wrote : — for, certainly, no individual, who is com- 

 petently acquainted with the steam-engine, and with the appli- 

 caition of the rotative motion by the crank, would ever con- 

 clude that " therefore, all the difference must be attributed to 

 the application of the rotative motion by the crank, and to 

 the smallness of the engines,! since there are other causes to 



* It will be noticed by the reader, that the. writer of the article in 

 tlie North American Review, lays aside the smallness of the engines, and 

 attributes all the diiference to the single cause of changing the direction 

 of the power, from rectilinear to rotary,' 6y the methods in common prac- 

 tice. 



f In the article Steam Engine, Rees' Cyclopaedia, the author states, 

 that " There is, in the Philosophical Journal, a description of a con- 

 trivance by My. Samuel Clegg, for producing a rotative motion from a 

 reciprocating one, which not only simplifies the machine very much, but 

 exceeds the power of the common crank one-third." 



From this we learn what part of the supposed loss of power in the 

 steam-engine this writer would attribute to the application of the rota- 

 tive motion by tlie crank ; for, since he believed that Mr. Clegg's con- 

 trivance exceeds the power of the common crank one-third, it is plain 



