A.B. (^uinhy 011 Crank Motion. 317 



f is a small block of brass, which has grooves in its sides, 

 and which slides freely along between the two bars BB'. — 

 Through this block the brass pin Pp is let fall, which carries 

 on its lower end a pen or pencil. The thread th (which 

 passes through a hole at h) iscarried over the pulley m, and 

 down under the pulley n, and then along between the jiarallel 

 bars BJ3', and fastened to the block /. 



To those who have a knowledge of the properties of the 

 curve in question, it is plain, that if the extremity B' of the 

 parallel bars be pushed from us, the pin Pp will describe 

 (upon the table) the spiral of Archimedes. 



The curve. Fig. 7, Plate IV. is a spiral of Archimedes, as 

 described by this instrument. 



Ifwill be perceived that both branches of the curve are 

 here given ; and that the instrument, in its present state, de- 

 scribes the two branches successively; and likewise that the 

 two branches described are, necessarily, the two opposite 

 branches. By a small modification, the instrument would 

 describe'the two branches simultaneously. 

 Respectfully, your ob't servant, 



A. B. QUINBY. 

 .New- York, Nov. 4, 1824. 



Art. XVI. — On Crank Motion, in reply to the remarks of 

 the author of a Review in the North American. 



TO THE EDITOR. 

 Sir, ' • 



I NOTICE in the last number of your Journal of Science and 

 Arts a reply from the writer of the article in the North 

 American Review to the Note I added to my solution of the 

 Crank Problem. 



In answering this reply, I shall ende-avoOr to be perspicu- 

 ous; and as 1 have now "hunted up some information on 

 the subject,'' I hope to be ab'e to convince the ingenious 

 writer of that article, not that he noiv believes that the crank 

 occasions a loss of threefourths of the whole power, but 

 merely that when he wrote the article in the North American 



