356 Rejoinder of Mr. Quinby on Crank Motion. 



Art. XII. — Rejoinder of Mr. Quinby to the writer of the 

 examination of his Principle of Crank Motion. 



TO THE EDITOR. 



Sir — The allusion, which the writer of the article entitled, 

 '" Examination of Mr. Quinby 's Principle of Crank Motion," 

 has made in the last number of this Journal, to a private 

 communication from yourself to me, makes it necessary for 

 me to state to the public, all the facts relative to the commu- 

 nication alluded to. By referring to my reply it will be seen 

 that it is dated March 28. The private letter I received from 

 you, in which you communicated the errata you had receiv- 

 ed from the writer of the ' examination,' is dated April 28 ; 

 and was received by me two days after that date. The fol- 

 lowing is a copy of that part of your letter, which relates to 

 the errata you communicated. 



" I requested a mathematical friend to look over your late 

 communication, in reply to the writer who criticises you, and 

 to compare it with a list of errata which had been forwarded 

 to me, by the author alluded to above." In reply, my friend 

 has handed to me the following remarks : — 



" Among the errors pointed out by , the only one no- 

 ticed by Mr. Quinby, is that which occurs at page 126, line 14 

 from the top, where, (as would seem from the printed demon- 

 stration,) Cc and Ce, two unequal lines, are found to be the 

 same. This was an error of the author, for it is printed pre- 

 cisely as it stood in the MS. Yet it is not altogether candid 

 in Mr. Quinby to avail himself of it, for it is evident that the 

 writer intended to have the terms taken alternately, though 

 he forgot to repeat them in that order. Thus, as printed, it 

 stands as follows: — 



am : aS :: Cc : CS 

 dn : aS :: Ce : Ct 

 where the writer infers, that the third terms are the same ; 

 he evidently should have said the second, namely, aS. But 

 his conclusion is correct, and is precisely the same as though 

 he had taken the terms alternately, in which case aS would 

 become the third term in each couplet, viz. am : Cc :: aS : CS 

 and dn : Ce :: aS : Ct : the whole error consists in acciden- 

 tally saying third for second — a mistake evidently accidental, 

 and one which it is unfair for a disputant to avail himself of, 

 as every reader will perceive." 



