18 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XIX.) 
be right-handed, or according to the direction expressed by the 
arrow heads on the circle c ; if the ray proceed from b to a, and 
the eye be placed at a, the rotation will still be right-handed to 
the observer , i. e. according to the direction indicated on the 
circle d. Let now an electric current pass round the oil of 
turpentine in the direction indicated on the circle c, or magnetic 
poles be placed so as to produce the same effect (2155.) ; the 
particles will acquire a further rotative force (which no motion 
amongst themselves will disturb), and a ray coming from a to 
b will be seen by an eye placed at b to rotate to the right-hand 
more than before, or in the direction on the circle c ; but pass a ray from b to a, 
and observe with the eye at a , and the phenomenon is no longer the same as before ; 
for instead of the new rotation being according to the direction indicated on the circle 
d, it will be in the contrary direction, or to the observer’s left-hand (2199.). In fact 
the induced rotation will be added to the natural rotation as respects a ray passing 
from a to b, but it will be subtracted from the natural rotation as regards the ray 
passing from b to a. Hence the particles of this fluid which rotate by virtue of their 
natural force, and those which rotate by virtue of the induced force, cannot be in 
the same condition. 
2233. As respects the power of the oil of turpentine to rotate a ray in whatever 
direction it is passing through the liquid, it may well be, that though all the particles 
possess the power of rotating the light, only those whose planes of rotation are more 
or less perpendicular to the ray affect it ; and that it is the resultant or sum of 
forces in any one direction which is active in producing rotation. But even then a 
striking difference remains, because the resultant in the same plane is not absolute 
in direction, but relative to the course of the ray, being in the one case as the circle 
c, and in the other as the circle d , fig. 3 ; whereas the resultant of the magnetic or 
electric induction is absolute, and not changing with the course of the ray, being 
always either as expressed by c or else as indicated by d. 
2234. All these difference^, however, will doubtless disappear or come into 
harmony as these investigations are extended ; and their very existence opens so 
many paths, by which we may pursue our inquiries, more and more deeply, into the 
powers and constitution of matter. 
2235. Bodies having rotating power of themselves, do not seem by that to have a 
greater or a less tendency to assume a further degree of the same force under the 
influence of magnetic or electric power. 
2236. Were it not for these and other differences, we might see an analogy be- 
tween these bodies, which possess at all times the rotating power, as a specimen of 
quartz which rotates only in one plane, and those to which the power is given by 
the induction of other forces, as a prism of heavy glass in a helix, on the one hand ; 
and, on the other, a natural magnet and a helix through which the current is passing. 
Fig. 3. 
