Intelligence and Miscellaneous Articles. 317 



that if two equivalent groups be transmitted through any optical 

 train, and be afterwards analysed, they will present exactly the same 

 appearance ; so that equivalent groups may be regarded as optically 

 identical. 



It readily follows from the above theorem, that any group of 

 polarized streams is equivalent to a stream of common light com- 

 bined with a stream of elliptically-polarized light from a different 

 source. If J, J' be the intensities of these streams, a' the azimuth 

 of the plane of maximum polarization of the latter, tan /3' the ratio 

 of the axes of the characteristic ellipse, 



J=A- V(A°~ + B 2 + 0) ; J'= a/(A2 + B* + C=) ; 



sin 2/3'=-^ — 7 — ; tan2&'=2.. 



' a/(A* + B 2 + C 2 ) c 



The author has applied these formula? to a few examples, and has 

 likewise shown, from the general principles established in the paper, 

 that the changes which are continually taking place in the epoch and 

 intensity of the vibrations of polarized light may be of any nature. 

 In the case of common light, the author contends that there is no 

 occasion to suppose the transition from a series of vibrations of one 

 kind to a series of another kind to be abrupt, but that it may be of 

 any nature. 



XLV. Intelligence and Miscellaneous Articles. 



ON GAS-BATTERIES, AND ON THE PREPARATION OF HYDRIODIC 

 AND HYDROBROMIC ACIDS BY THE GALVANIC METHOD. BY 

 M. OSANN. 

 ri^HE pluenomena exhibited by a circuit composed of gaseous ele- 

 -*- ments appear at first sight to be explicable in the following manner. 

 One of the tubes contains hydrogen, the other oxygen, both of which 

 are over dilute sulphuric acid, but in such a manner that the ends of 

 the two strips of platinum existing in the tubes dip into the liquid. 

 Now as oxygen is somewhat soluble in dilute sulphuric acid, the 

 strip of platinum in the hydrogen element comes into contact with 

 hydrogen and the oxygen dissolved in the acid, and as platinum 

 possesses the property of causing the two gases to combine, the 

 simplest view seems to be that this combination occurs in the present 

 case, and that the electric current is produced by this chemical action. 

 But the following well-founded objection may be urged against this 

 view. When oxygen and hydrogen combine, whether this arise from 

 the inflammation of burning bodies, from the electric spark, or from 

 finely divided platinum, considerable heat is produced ; but in the 

 present case this is absent, for elevation of temperature is never per- 

 ceived. The action of the platinum must therefore be of a different 

 kind here. It might lie said, that in this case the platinum trans- 

 formed the hydrogen into the same state as that in which it exists 

 in the hydrogen-acids, which are decomposed in the well-known 

 way by oxides, without simultaneous elevation of temperature from 



