Michael Faraday, his Life and Works, 167 
the right, and others to the left of the observer. The discov- 
ery of Faraday was that the influence of magnetism or of elec- 
tric currents develop this same property in nearly all transpar- 
ent substances, but with this difference, that the direction of 
rotation of the plane of polarization depends only upon the 
position of the magnetic poles, or the direction of the currents 
with relation to the transparent substance, The law is that 
if the north pole of the electromagnet is placed on the same 
side as the observer who receives the ray into his eye, and con- 
sequently the south pole on the side by which the polarized 
ray enters into the substance, the rotation of the plane of po- 
larization takes place, to the observer, from left to right. 
takes place from right to left if the direction of the current, 
and consequently that of the magnetization, be changed. The 
action of the magnet may be replaced by that of a coil in the 
axis of which the transparent substance is placed. In this 
case, again, the rotation of the plane of polarization is v 
bserv 
s 
through the wire of the coil ; and the direction of the rotation 
is always the same as that of the current. 
Thus, whilst in substances naturally endowed with circular 
polarization the rotation of the plane of polarization always 
takes place, according to the nature of the substance, either to 
the right or left of the observer, in Faraday’s experiment the 
direction of this rotation only depends upon the direction of 
electric currents or the relative position of the magnetic poles, 
since it is completely independent of the position of the ob- 
server. These two kinds of action are therefore not identical, 
1s allowed to escape, and doubles, triples, or “scx as the 
ray is reflected once, twice, or three times. But when, instead 
of the magnetic, we have to do with the natural — po- 
: & . oat . re- 
