C. GENERAL PHYSICS. 151 



THE MATHEMATICAL THEORY OF LIGHT. 



An exhaustive memoir on the interference of light, by- 

 Professor Lommel, is contained in the Proceedings of the 

 Physical Society of Erlangen, in which he brings the phe- 

 nomena of thick and thin plates of glass and of curved surfaces 

 into one point of view. Some of the diagrams given by him re- 

 mind one strongly of those multiplex curves treated of by Pro- 

 fessor Newton in the Connecticut Academy of Sciences for 

 1874. Sitzb. Fhysikal.-Med. Gesells.^Miangen^ 1875, 106. 



MATHEMATICAL THEORY OF LIGHT. 



The connection between the elliptic polarization of light 

 reflected from mirrors, and the refraction and dispersion of 

 light when passing through transparent media, is developed 

 in a very elaborate manner by Ketteler, who deduces a 

 complete theory from the consideration of the expression 

 A+BV 1, which expression Fresnel met with in his inves- 

 tigation of the subject of total reflection. The occurrence of 

 this expression, to which the term " complexe " is given by 

 the French and German mathematicians, is shown by Ket- 

 teler to result from the fact that the \vave of light reflected 

 from any surface may be considered as a complex wave, 

 consisting of a superposition of two partial waves differing 

 from each other by one quarter of a wave-length. The in- 

 terpretation which Fresnel himself seems to have given is 

 submitted to a riofid demonstration. Ketteler states that we 

 are led more and more to the conviction that in all dioptrical 

 phenomena we have to do not so much with a special con- 

 stitution of the optical ether as with the synchronous vibra- 

 tion of the atoms of ether, and those of material bodies; and 

 that, in fact, the ether itself may have the same inertia and 

 density within as without the transparent body. His mem- 

 oir is especially devoted to the development of the idea 

 that there is a vibration of the ponderable atoms correspond- 

 ing to the vibrations of the ether. Verhandl. Naturhist. Ver- 

 eins, BoJin, XXXII., 1 to 224. 



DEEr-SExl SOUNDING BY PHOTOGRAPHY. 



Dr. Neumayer has presented to the Geographical Society 

 of Berlin a remarkable photographic apparatus for determin- 



