318 A. B. (^uinby on Crank Motion. 



Review, he did believe that the crank occasions a loss oi 

 three-fourths of the whole power employed ! ! 



" There is," says this writer, " in the steam-engine, a loss 

 of power in changing the direction of its action from rectili- 

 near to rotary, by the mtehodsin common practice,^'' &.C.; which 

 on an average amounts to about three-fourths of the whole 

 power, as appears from the reports on the performance, of the 

 engines used at the mines in Cornwall." 



Now it is certainly not difficult, for any person who can 

 comprehend plain language, to understand what is ex- 

 pressed in the above quoted sentence. " There is, in the 

 steam-engine, a loss of power, m changing the direction of its * 

 action from rectilinear to rotary, by the methods in common 

 practice.''^ Can any words convey a clearer or more definite 

 meaning than these here used : — for does not every individual, 

 who has the least knowledge on the subject of the construc- 

 tion of the steam-engine, know that "the method in common 

 practice," for changing the direction of the power from rec- 

 tilinear to rotary, is the crank F And yet the writer of the 

 article in question boldly asks, " Can any one pretend, for 

 one moment, that there is any thing in this paragraph which 

 warrants Mr. Quinby's assertion that the loss of power is sup- 

 posed to result from the crank V 



But there is something more conclusive to be said on this 

 subject. In Rees' Cyclopaedia, article steaVn-engine, we have 

 the following words : " Before quitting the subject of double 

 engines,* [double cylinder engines,] employed to give a rota- 

 tive motion to machinery by a crank, we must notice the re- 

 markable difference, shown by Messrs. Leans' reports, be- 

 tween the performance of the small engines employed in 

 drawing the matter out of the mines, and those used in 

 pumping water." 



•" We should think the loss of power from friction, in draw- 

 ing up buckets by a rope, could not be greater than the fric-' 

 tion of pump buckets, and of the water moving in the pipes; 

 therefore, all the difference must be attributed to the applica- 

 tion of the rotative motion, [by the cranky and to the small- 

 ness of the engines; these are usually 14, 16, and 24 inches 



* Those who are familiar with the construction of different kinds of 

 engines, will perceive, by reading- the article steam-engine, in Rees' 

 Cyclopaedia, that the engine here meant is Woolf's double cylinder en- 

 gine, and not the double engine invented by Watt. 



