Sheldon — Magneto-optical Generation of Electricity. 197 



Sow if a difference of potential, under these conditions, pro- 

 duces such a rotation of the plane, why should not a rapid rota- 

 tion of the plane under exactly the same conditions produce an 

 inverse difference of potential between the terminals of the coil ? 

 A continuous rotation should produce a continuous current of 

 electricity and an oscillating of the plane an alternating cur- 

 rent. The experiments which have been performed verify the 

 latter supposition. 



The coil employed was wound upon a thin brass tube as a 

 core. This was closed at each end by plates of glass and was 

 provided with holes for filling with carbon bisulphide. Its 

 length was 175 mm and its diameter 23 mm . Upon this was 

 wound the coil from double silk-covered copper wire of 

 0'85 mm diameter. When wound the length of the coil was 

 150 mm and its diameter 45 mm . The resistance was 7*21 ohms. 



A quantitative measurement of the Faraday effect was first 

 made and in the following manner : A beam of light from 

 an incandescent lamp, after passing through a large nicol, 

 was made to traverse the bisulphide of carbon in the coil. 

 Upon emerging the beam was brought to extinction by the 

 proper adjustment of an analyzing nicol. A measured current 

 of electricity was now passed around the coil. This necessi- 

 tated a readjustment and rotation of the analyzing nicol to re- 

 produce extinction of the beam. Within the limits tried this 

 rotation was proportional to the current strength. As a mean 

 of many measurements it was found that a current of 1 ampere 

 required a rotation of 78 minutes of the analyzer. Accord- 

 ingly 278 amperes would be required to rotate the plane 

 through 360°, providing the proportionality between current 

 strength and rotation remained unaltered. 



Sow, if we consider a plane polarized ray of light to be 

 made up of two opposite circularly polarized rays, then a parti- 

 cle of ether in the bisulphide of carbon describes a simple har- 

 monic oscillation in a plane. This motion in a straight line 

 is the resultant of the two oppositely directed, equiperiodic, 

 circular rotations of equal amplitude. If now a magnetic held 

 be created, the particle undergoes an instantaneous circular 

 electric displacement which results in the retardation of one 

 and the acceleration of the other component rotation. The 

 line of oscillation suffers rotation as a result, and assumes a 

 new position. The displacement must be instantaneous, for, 

 were it continuous, the line of oscillation would continue to 

 rotate and the analyzer could not be made to produce extinc- 

 tion. If now, instead of allowing the magnetic field to pro- 

 duce this circular displacement, we superimpose, by mechani- 

 cal means, a third rotation upon the two existing components, 



Am. Jour. Sci. — Third Series, Vol. XL, No. 237. — Sept., 1890. 

 13 



