C. GENERAL PHYSICS. 137 



riod, can have its vibrations completely extinguished by at- 

 taching to it an elastic thread of a proper length and sus- 

 ceptible of transverse' vibrations, in a plane parallel to that 

 of the vibrations of the body. 6 Z?, 1873, 671. 



THE ELLIPTIC POLAPJZATION OF LIGHT. 



Wiedemann has investigated the elliptic polarization of 

 light, and its relations to the superficial colors of bodies. 

 His observations show that the semi-metallic bodies behave, 

 in reference to the rate of retardation in their transparent 

 parts, similarly to the transparent bodies themselves ; but in 

 their opaque parts they behave similarly to the metals. 

 Again, the more that light of a given wave-length is absorb- 

 ed by any body, by so much the greater is also the ellipticity 

 of the vibrations when reflected from the body. And, again, 

 the colors that are best reflected show, in general, the strong- 

 est elliptic polarization. The principal angle of incidence is 

 subjected to the greatest variations for light whose wave- 

 lengths correspond nearly to the absorption bands. Inau- 

 gural Dissertation, Berlin, ]873. 



PLATEAU'S GLYCERIC LIQUID. 



Professor Brush refers to the following mixture, as being 

 easier to prepare than the so-called Plateau's glyceric liquid, 

 as well adapted to the production of the beautiful soap- 

 bubbles, and other thin films, whose remarkable properties 

 Professor Plateau has so successfully studied during the past 

 twenty years. One gramme of dry Marseilles soap is dissolved 

 in one hundred grammes of warm water. This is filtered, 

 and to every hundred cubic centimeters of the solution forty 

 Grammes of white sugar are added. Bubbles made with this 

 liquid will last several hours. For illustrating the colors of 

 thin films, a copper ring fifteen centimeters in diameter, of 

 wire the fifth of an inch thick, is used, which is mounted 

 vertically on a stand, and can be covered with a bell-glass. 

 A portion of the liquid being poured into a plate, the ring is 

 laid flat on its surface, and on removal a film of the liquid 

 will adhere to it. Covering the ring with gutta-percha var- 

 nish facilitates this adherence. The ring is then mounted 

 vertically on its stand, and on viewing it at an angle of 45 

 beautiful bands of color are observed successively changing, 



