C. GENERAL PHYSICS. 157 



solvents, are stated by Charles Horner to exhibit this phe- 

 nomenon when dissolved in castor-oil ; and other substances 

 which he dissolved in alcohol show this property with aug- 

 mented intensity when treated with castor-oil. To obtain 

 clear solutions, the materials are first boiled, then filtered, 

 evaporated to dryness, and again dissolved in oil under the 

 influence of heat. The fluorescence disappears when hot, 

 but returns on cooling. A number of facts are given by him 

 showing the increased intensity of the fluorescence of these 

 solutions, and suggesting the importance of taking advantage 

 of this property in studying the phenomena; in fact, it seems 

 that fluorescence is a property of solutions rather than of 

 simple substances. 7 A, XLVIIL, 165. 



THEORIES OF MAGNETISM AND LIGHT. 



Boltzmann has experimentally confirmed the theory that 

 Iio"ht and electricity are only different forms of motion of one 

 and the same medium, by showing that from it there should 

 result a certain relation between the refractive power of a 

 substance and its dielectric properties, a relation confirmed 

 by observation. A further confirmation of the same theory 

 has also been lately published by Boltzmann, based on investi- 

 gations into the behavior of non-conducting bodies under the 

 influence of electric forces. He says that, according to Max- 

 well's theory, the constant of dielectricity for non-isotropic 

 crystallized bodies must depend upon the direction in which 

 the electric forces act upon it, varying in a manner such as 

 can be predicated from the optical properties of the body. 

 The only double refracting crystals that are appropriate to 

 the investigation are those of sulphur. Two spheres cut 

 from crystals of sulphur, whose optical axes had been pre- 

 viously determined, were experimented with by allowing the 

 electricity to act in various directions in reference to the op- 

 tical axes. In this manner the magnetic axes, as they may 

 be called, were determined, and were shown to agree with 

 the optical axes; and the same results being arrived at from 

 both spheres, be concludes that these observations not only 

 confirm Maxwell's theory as to the nature of electricity, but 

 also definitively decide that the vibrations of ether forming 

 liojht are perpendicular to the plane of polarization. 19 C, 



vm., 105. 



