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Difference between the Magnetic and Natural Rotation. 313 



to a current ; as in magnets, according to Ampere's theory, 

 the state is a state of current. When a core of iron is put 

 into a helix, every thing leads us to believe that currents of 

 electricity are produced within it, which rotate or move in a 

 plane perpendicular to the axis of the helix. If a diamag- 

 netic be placed in the same position, it acquires power to make 

 light rotate in the same plane. The state it has received is a 

 state of tension, but it 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 exists in diamagnetics, under 

 such circumstances, a tendency to currents, is consistent with 

 all the phaenomena as yet described, and is further strength- 

 ened by the fact, that, leaving the loadstone or the electric 

 current, which by inductive action is rendering 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 mole- 

 cular condition of a body, required to produce the circular 

 polarization of light, has been artificially given ; and it is there- 

 fore very interesting to consider this known stats and condi- 

 tion 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 chemically speaking, being in the latter instance 

 a liquid with particles free to move, presents different speci- 

 mens, 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 arrange- 

 ment 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 simul- 

 taneously 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 turpentine by the magnetic or electric forces : 

 it exists only in one direction, i. e. in a plane perpendicular 



