AND STRAIN ON THE ACTION OF PHYSICAL FORCES. 
155 
The Effect of Longitudinal Magnetization on the Electrical Resistance 
of Zinc Foil. 
Experiment LXXII. 
A piece of commercial zinc foil/14 inches in length and '040 millirn. in thickness, was 
wrapped lengthwise round a soft iron bar of circular section, / inch in diameter and 
15 inches in length, which had previously been coated with two layers of brown paper. 
The width of the foil was such that when wound round the bar the edges just over¬ 
lapped. The foil was secured in position by fine yet strong twine, and having been 
covered with two folds of brown paper the whole was placed centrally in the coil A. 
At the two ends the foil was cut so as to allow of these ends being clamped in the 
usual manner in brass blocks, and a strip of foil of similar dimensions served as the 
comparison-piece. The same mode of experimenting and the same precautions were 
taken as with the bismuth bar. Seven Grove’s cells were used for the M.C., and 
these produced a deflection of 15° of the needle of the tangent galvanometer. Several 
trials which accorded very fairly with each other showed a mean increase of resistance 
represented by 3'8 divisions of the scale. The M.C. was reversed, and again several 
trials showed an increase of resistance, the mean value of which was represented by 
3'5 divisions. From the data obtained it was calculated that the increase of resist¬ 
ance amounted to ‘0148 per cent. The iron core having been removed no appreciable 
change in the resistance of the zinc foil could be detected on passing the M.C. 
The Effect of Longitudinal Magnetization on the Electrical Resistance 
of Copper Wire. 
Experiment LXXIII. 
A piece of silk-covered copper wire, 12 feet in length and g^th of an inch in 
diameter, was doubled backwards and forwards so as to form a bundle 1 foot in 
length. The whole was then well coated with shellac varnish, and when dry inserted 
into one of the copper coolers (fig. 19), which was placed in the coil A. A similar 
bundle served as the comparison-piece, and the two bundles were connected up in the 
usual manner with the bridge. One Grove’s cell was used for the E.C., and the 
deflection of the tangent galvanometer produced by the M.C. was 16°. The B.C. was 
kept on for 10 minutes, and whilst still on the following readings were taken :—• 
