at 2. ney on Crank Motion. 31 
mt 
fisa small ock of brass, which has grooves in its sides 
and w 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 A) ,is carried over the pulley m, and 
down under the pulley », and then along between the a a 
bars BB’, and fastened to the block f. 
To those who have a knowledge of the properties 
curve in question, it is plain, that if, the extremity B’ o 
parallel bars be pushed from ee the pin. Pp will describe 
(upon the table) the spiral of Arcl limed es. 
he curve, Fig. 7, Plate IV. is a spiral of ‘Archimedes, as 
described by-this D andinenk 
It will 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 simultaneous 
Respectfully, your ob’t servant, 
eueas 
Ae Bo QUINBY. 
New-York, Nov. 4, 1824, te 
Arr. XVL.- — On Crank Motion, in reply to the remarks of 
the author of a Review in the North American. 
* TO THE EDITOR. ass = 
Sir, Y 
I norice in the Jast number of oie Jone of Seience and 
Arts a reply from the writer of the article in the Nort 
American Review to the Note I added to my solution of nau 
Crank Problem. 
In answering this reply, I shall endeavour to sae perspicu- 
ous; and as | have now “hunted u ssome information on 
the subject,” I hope to be able to convince the ingenious 
writer of that article, not that he now believes that the crank 
occasions a loss of three-fourths of the whole power, but 
‘merely that when he wrote the article in the Nofth American 
