4 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XIX.) 
tion being - to an equal degree in extent as before. The direction was always the same 
for the same line of magnetic force (2149.). 
2156. When the diamagnetic was placed in the numerous other positions, which can 
easily be conceived, about the magnetic poles, results were obtained more or less 
marked in extent, and very definite in character, but of which the phenomena just 
described may be considered as the chief example : they will be referred to, as far as 
is necessary, hereafter. 
2157. The same phenomena were produced in the silicated borate of lead (2151.) 
by the action of a good ordinary steel horse-shoe magnet, no electric current being 
now used. The results were feeble, but still sufficient to show t lie perfect identity of 
action between electro-magnets and common magnets in this their power over light. 
2158. Two magnetic poles were employed end-ways, i. e. the cores of the electro- 
magnets were hollow iron cylinders, and the ray of polarized light passed along their 
axes and through the diamagnetic placed between them : the effect was the same. 
2159. One magnetic pole only was used, that being one end of a powerful cylinder 
electro-magnet. When the heavy glass was beyond the magnet, being close to it 
but between the magnet and the polarizing reflector, the rotation was in one direc 
tion, dependent on the nature of the pole ; when the diamagnetic was on the near side, 
being close to it but between it and the eye, the rotation for the same pole was in 
the contrary direction to what it was before ; and when the magnetic pole was 
changed, both these directions were changed with it. When the heavy glass was 
placed in a corresponding position to the pole, but above or below it, so that the 
magnetic curves were no longer passing through the glass parallel to the ray of 
polarized light, but rather perpendicular to it, then no effect was produced. These 
particularities may be understood by reference to fig. 1, where a and b represent the 
first positions of the diamagnetic, and c and d the latter posi- 
tions, the course of the ray being marked by the dotted line. If 
also the glass were placed directly at the end of the magnet, 
then no effect was produced on a ray passing in the direction 
here described, though it is evident, from what has been already 
said (2155.), that a ray passing parallel to the magnetic lines 
through the glass so placed, would have been affected by it. 
2160. Magnetic lines, then, in passing through silicated borate of lead, and a great 
number of other substances (2173.), cause these bodies to act upon a polarized ray 
of light when the lines are parallel to the ray, or in proportion as they are parallel to 
it : if they are perpendicular to the ray, they have no action upon it. They give the 
diamagnetic the power of rotating the ray ; and the law of this action on light is, that 
if a magnetic line of force be going from a north pole, or coming from a south pole, 
along the path of a polarized ray coming to the observer, it will rotate that ray to 
the right-hand ; or, that if such a line of force be coming from a north pole, or going 
from a south pole, it will rotate such a ray to the left-hand. 
