DIFFERENCE BETWEEN THE MAGNETIC AND THE NATURAL ROTATION. 17 
has not passed on into currents, though the acting force and every other circumstance 
and condition are the same as those which do produce currents in iron, nickel, cobalt, 
and such other matters as are fitted to receive them. Hence the idea that there ex- 
ists in diamagnetics, under such circumstances, a tendency to currents, is consistent 
with all the phenomena as yet described, and is further strengthened by the fact, 
that, leaving the loadstone or the electric current, which by inductive action is render- 
ing a piece of iron, nickel, or cobalt magnetic, perfectly unchanged, a mere change of 
temperature will take from these bodies their extra power, and make them pass into 
the common class of diamagnetics. 
2230. The present is, I believe, the first time that the molecular condition of a body, 
required to produce the circular polarization of light, has been artificially given ; and 
it is therefore very interesting to consider this known state and condition of the 
body, comparing it with the relatively unknown state of those which possess the 
power naturally: especially as some of the latter rotate to the right-hand and others 
to the left ; and, as in the cases of quartz and oil of turpentine, the same body chemi- 
cally speaking, being in the latter instance a liquid with particles free to move, pre- 
sents different specimens, some rotating one way and some the other. 
2231. At first one would be inclined to conclude that the natural state and the 
state conferred by magnetic and electric forces must be the same, since the effect is 
the same ; but on further consideration it seems very difficult to come to such a 
conclusion. Oil of turpentine will rotate a ray of light, the power depending upon 
its particles and not upon the arrangement of the mass. Whichever way a ray of 
polarized light passes through this fluid, it is rotated in the same manner; and rays 
passing in every possible direction through it simultaneously are all rotated with equal 
force and according to one common law of direction ; i. e. either all right-handed or 
else all to the left. Not so with the rotation superinduced on the same oil of turpen- 
tine by the magnetic or electric forces : it exists only in one direction, i. e. in a plane 
perpendicular to the magnetic line ; and being limited to this plane, it can be changed 
in direction by a reversal of the direction of the inducing force. The direction of 
the rotation produced by the natural state is connected invariably with the direction 
of the ray of light ; but the power to produce it appears to be possessed in every 
direction and at all times by the particles of the fluid : the direction of the rotation 
produced by the induced condition is connected invariably with the direction of the 
magnetic line or the electric current, and the condition is possessed by the particles 
of matter, but strictly limited by the line or the current, changing and disappearing 
with it. 
2232. Let m, in fig. 3, represent a glass cell filled with oil of turpentine, possessing 
naturally the power of producing right-hand rotation, and a b a polarized ray of 
light. If the ray proceed from a to b, and the eye be placed at b , the rotation will 
mdcccxlvi. n 
