PROFESSOR THOMSON ON THE ELECTRO-DYNAMIC QUALITIES OF METALS. 743 
166. Still, as the preceding experiment (Exp. 3) had appeared (§ 159) to show that 
the absolute conductivity is diminished in all directions by magnetization, it seemed 
possible that the effect now observed might be caused by inequalities in the distri- 
bution of magnetism in the plate. Thus if from the character of the distribution of 
the magnetizing force, or because of non-uniformity in the plate, the parts between 
C and B and between A and E were less intensely magnetized, and those between 
C and A and between B and D more intensely magnetized, than the average, the 
observed effect could be accounted for without any difference in the electric conduc- 
tivity of the substance in the different directions. To test this conceivable explana- 
tion, pieces of soft iron (cubes and little square bars nearly double cubes) were laid 
over the square plate, being kept insulated from electric communication with it by 
paper, so that while the conducting mass remained unchanged, the distribution of 
the magnetization of its substance might be altered. Before the magnetic force was 
applied, a great effect on the neutral point of the multiplying branch was observed, 
taking place gradually during several minutes, and obviously due, in a great measure, 
to variation of the distribution of temperature in the conducting square. (See below, 
§ 177, for an illustration of this effect.). When a new neutral point was found, the 
magnet was made, reversed, unmade, &c., and always with the same effects as 
before. Different arrangements of the little masses of soft iron produced different 
absolute effeets on the neutral point, causing it to shift sometimes as much as fifteen 
inches on the multiplying branch, but the effects of magnetism were invariably found 
to be consistent with the first-mentioned result. As the distribution of the magnet- 
ism in the square plate must have varied very much under these different circum- 
stances, and in all probability must have been in some of the cases more intense in 
the quarters towards AE and CB than in those towards AC and DB, the conclusion 
could scarcely be avoided, that the conductivity of the magnetized substance was 
greater across than along the lines of magnetization. For the purpose of further 
testing and illustrating this conclusion I planned the following experiment, to com- 
pare directly the resistances of two equal and similar squares of sheet iron, equally 
and similarly magnetized, arranged in the same circuit to conduct electricity across 
the lines of magnetization of one and along those of the other. 
167. Exp. 5. To compare the conductivities of magnetized iron along and across 
the lines of magnetization. — A piece of sheet copper, BCHK (fig. 48), 3 inches long, 
2 broad and ^ inch thick, was bent round the line FH into the form shown in fig. 49. 
Fig. 48. Fig. 49. Fig. 50. 
A square of thin sheet iron, 2 inches wide (weighing 103 grains), was soldered by 
one side to the edge CH of the copper in the position shown in fig. 50. The pro- 
