Intelligence and Miscellaneous Articles. 361 



vanishing increments when mapped out on the scale of the 

 molecular pressures of liquids and solids. It is from this 

 point of view that I am about to make further experiments on 

 the thermodynamics of fluid matter. 



Physical Laboratory, U.S. Geological Survey, 

 Washington, D.C., U.S.A. 



XL. Intelligence and Miscellaneous Articles. 



THE MAGNETO-OPTICAL GENERATION OF ELECTRICITY/. 

 BY SAMUEL SHELDON, PH.D. 



T\7HILE experimenting upon the effects of alternating currents 

 ^ of electricity upon the plane of: polarized light, results were 

 obtained which made it feasible to try a series of experiments, in 

 which the Faraday arrangements were reversed. Although the 

 series is incomplete, yet the little that has been accomplished 

 seems worthy of publication. 



It is well known * that if a beam of plane-polarized light be 

 passed through a tube containing bisulphide of carbon, and if the 

 tube and beam lie in the direction of the lines of force of an 

 electromagnet about to be excited, the plane of the emergent beam 

 will be rotated upon exciting the magnet. The direction of 

 rotation will be the same as that of the exciting current, and the 

 amount of rotation will depend upon the strength of the current. 

 If the current be reversed, the plane will be rotated in an opposite 

 direction and by exactly the same amount. Thus the rapidly 

 alternating current would produce a rapid swinging to and fro of 

 the plane of light. 



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

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

 of the plane under exactly the same conditions produce an inverse 

 difference of potential between the terminals of the coil ? A con- 

 tinuous rotation should produce a continuous current of electricity, 

 and an oscillating of the plane an alternating current. The ex- 

 periments 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 millim. and its diameter 23 millim. Upon this was wound 

 the coil from double silk-covered copper wire of 0-85 millim. dia- 

 meter. When wound, the length of the coil was 150 millim. 

 and its diameter 45 millim. 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, 



* Faraday, Exp. Ees. 2146, vol. iii. p. 1. 



