PRODUCED BY ALTERNATING ELECTRIC CURRENTS. 
289 
sin 2a + 3 (sin 2y + sin 2 y) + sin 2a — 2 y — sin 2a — 2y 
— 3 sin 2 y — 2y — 9 sin 2a — 2y — 2y\ 
Fig. 23. 
For the other shed, we interchange y and y. 
For the couples to be equal and opposite when y — tt — y, we must have a = 0 
or \tt. When y = the a, b couple is positive for both values of a, and when 
y = -g-77, it is negative. 
We now take as an example 
y = tt/ 6, y = tt/3, 
and the a , b couple is negative from 0° to about 98° 23', positive thence to 171° 37' 
and negative to 180°. The a, b' couple is negative from 0° to 112° 34', positive 
thence to 157° 26' and negative to 180°. 
In fig. 26, a = 45°; in fig. 27, a = 105°. 
Fig. 26. Fig. 27. 
2 P 
MDCCCXCII.—A. 
