LENZ ON ELECTRO-MAGNETISM. 627 
in terms of the diameter of the cylindrical armature, and the thickness 
of the wire and its silky envelope. We have however the semi-dia- 
meter of a convolution, if half the thickness of the iron cylinders is = g, 
for the first series = g + 6 —t B 
second a +3 (6 + B) 
: 5 
—— third ——=4¢+ 5 +8) 
whence we have the length of a convolution or 
efor the first series = (29 +(b+ 6)) 7 
e — second = (29+ 3+ B)) 
c — third = (29 +5(6+ B)) 7 
c ath — = (29+ (@n—1)(+6))* 
If we substitute the first value of ¢ in the equation for m, we obtain 
ab? f 
Pian (29+ (b+ B)) + (b+ B)m’ 
The electromotive power is for two seriesof convolutions with regard 
to the above law, No. 2, 
Se phi A ae 
oral 
but the resistance is equal to that of the two series of convolutions, 
; am with the piece m, therefore 
6+ 5 p2qtb+B)r+ paz 29 +3(6+6))x +m 
— b2 
a Eg ae Oe) i EE.) 
B(b + 6) 
consequently the power of the current for two series, or 
2 al je ees 
Po~anr(4g+46+6))+m(O+ B) 
b? (6 + B) 
2 a 62 
~ an(gt4O+ uF) + m(b + B) 
Vou. lL—Parr IV. 20) 
