Mr. Quinby's reply to Mr. Blake. 73 



ery, and as conceived in an improper spirit. In inserting 

 them, we were not impressed with any other idea, than that 

 a practical man was urging a fair criticism respecting an in- 

 novation requiring great caution, and which was therefore a 

 proper subject of examination. We trust that it will be the 

 means of producing additional experiments, and that in the 

 end, the cause of truth — which should be the great object of 

 all our labors, will be promoted. — Editor. 

 July 20, 1827. 



Afttf . XI.—^Reply of Mr. Q.uinby to Mr. Blake's criticism on 

 his demonstration of the Crank Problem. 



To the Editor. 



Sir — In answering the criticism of Mr. Blake, in the recent 

 number of your Journal of Science and Arts, on the demon- 

 stration which I gave of the crank problem, it is only neces-. 

 sary to point out two misrepresentations which he has made 

 in the remarks he has offered. 



At page 341 he says, " But it appears from a part of Mr. 

 Q,ujnby's reasoning, the truth of which is admitted by his 

 opponent, that when CD represents the whole degree of force 

 exerted by the shackle bar on the crank, or, which is the 

 same thing, (the shackle bar being perpendicular,) the whole 

 degree of force exerted by the steam on the piston, then CG 

 represents the mean tendency to rotation in the crank which 

 that force produces." 



In the reasoning, to which Mr. Blake refers, it is demon- 

 strated that when CG, (not CD,) represents the " tendency 

 which P has to produce rotation," CG also represents the 

 " mean tendency which P',=P, has to produce rotation in de- 

 scending in the arc ADB." 



The second misrepresentation, which Mr. Blake has made, 

 is in supposing that the whole force and the mean force are 

 applied at different distances from the centre. In the demon- 

 stration which I gave I reduced the problem to the case of the 

 simple Pully, (or wheel and rack,) and supposed the whole 

 force and the mean force to be applied at the same point G. 



Since I reduced the problem to the case of the simple Pully, 

 (or wheel and rack,) and in that case considered the space 

 through which the power moves, it is plain that the demonstra- 

 tion which I gave is not liable to the objection which Mr. Blake 

 has stated. The demonstration, however, would be equally 



Vol. XIII.— No. 1. 10 



