316 A. B. Quinby on Crank Motion, 



see that the study of statistics is indispensable to arrive at 

 any degree of perfection, and the knowledge it procures is 

 an essential part of the science of the engineer in tracing 

 canals ; a truth which appears to have gone unheeded until 

 now, but which cannot be too loudly proclaimed since 

 public attention seems specially directed to that important 

 object. 



Paris, 1 7th June, 1 821 . 



Art. XII. — On crank motion; by A. B. Quinby, J^ew- 



York. 



The demonstration of the crank problem, or problem ior 

 deterraining'the mechanical power of the crank, offere'^ by 

 Mr Ward in the 4th vol. of your Journal of Science and 

 Arts, is, in my opinion, unsaiisfactory. 



It is not my wish to enter upon a review of all that Mr. 

 Ward has written on the subject of this important pro- 

 blem ; but I take the liberty to assert, that the principle 

 upon which his solution is founded, has never, to my knowl- 

 edge, been established. 



Mr. Ward says (p. 195), "The pressure of the steam 

 upon the piston being uniform through the stroke; it fol- 

 lows that the impulses (I understand upon the upper end of 

 the shackle-bar) at all times are equal to one another ; and 

 this being the case, it is equally a matter of course that the 

 effects produced at the several points of division of the 

 quadrant, are as the perpendiculars repectively from those 

 points to the line offeree.'' 



From what work on mechanics ; or, at what period, Mr. 

 Ward acquired his notions on the subjects of motion and 

 forces, shall not be my object to enquire : — my only object 

 is to show that the latter of the two inferences drawn in 

 the above quoted sentence is false ; and that to obtsin a 

 satisfactory result, in the case in question, we must attend 

 to matters which Mr. Ward's demonstration does not em- 

 brace. 



That the effects produced at the several points of divi- 

 sion of the quadrant are not as the perpendiculars respect- 

 ively from those points to the line of force, may be proved 

 in the following manner. 



