Examination of Mr. Quinby's Crank Motion. 125 
than W) at the distance Cv, through a space equal to that 
gone over by P in its descent, then the effective power of P 
applied at D is greater than that of an equal power acting at 
G ;—it is shown by Mr. Quinby, that the mean power of the 
crank is equal to the coustant force P acting at G,—thereforé 
less than P acting constantly at D,—therefore there would 
be a loss of power if the shackle bar were supposed to remain 
ical. 
Having, it is hoped, shown the fallacy of the attempt to 
prove that no power is lost in crank motion, it will be prop- 
er to say a few words upon the actual loss of power ; but first 
let me remark upon the manner in which Mr. Ward’s propo- 
sition, relative to the crank, is treated by Mr. Quinby. 
Mr. Ward’s idea is, that ‘‘ the effects produced at the sev- 
eral points of division of the quadrant, are as the perpendicu- 
ars respectively from these points to the lines of force.” Mr, 
Quinby denies this, and undertakes to prove the proposition 
to be incorrect; the error in his proof can easily be made evi- 
dent, by following the course of his demonstration. 
The circle ADBE (fig. 2) represents that in which the 
end of the shackle bar moves; aS and dt are two positions of 
the shackle bar, corresponding respectively to the points @ 
of the circle, ADBE, 
chanics, it is obvious that the value of P, estimated in the di- 
shackle bar when in the position Sa, is equal ope ts 5 
and the value of P in the direction ¢d, or the tension of the 
shackle bar, when in the position ¢d, is equal to Cae 
and (by mechanics) the tendency which P has to produce ro- 
