172 A. M. Mayer—LHffects of Magnetization 
long, placed at the distance of one foot from the center of the 
coil. This magnetic bar was furnished with scales precisely 
in the manner of an ordinary balance, and the weight required 
to bring it to a horizontal position indicated the intensity of 
the magnetism of the iron bar under examination. 
“ After a few preliminary trials, a great advantage was found 
to result from filling the tube with water. The effect of the 
water was, as De la Rive had already remarked, to prevent the 
sound. It also checked the oscillations of the index, and had 
‘‘ EXPERIMENT I. 
Deflection of Tangent of | Elongation or _Total Magnetic Square of magnet 
Galvanom- deflection. shostening. _ eongstiog._ inynelty inte eaatie- 
me I? 20° 128 ‘ LR 1:0 —0°49 240 
0 0 03 S. 0o-7 —0°42 252 
— 9 30 167 2-9 E. 3-6 —0°93 240 
ie fn 2-4 —0°%4 228 
14: 264 59 E. 8:3 1°42 243 
0 3°8 8. —1-00 222 
33 10 428 10:3 E. 14:8 — 1°87 236 
0 0 76S. 1-26 220 
—47 25 1088 161 E. 23°3 2/92 211 
13:9 S. . —1°35 194 
—58 50 1653 14:8 E. 24-2 ~— 9°31 202 
0 0 133 8. 10-9 —1°35 168 
Dr. Joule now reversed the current in the helix and found 
that a current which deflected the needle 6° 15’ shortened the 
