Srlrntijir Intel J 'J,/,-,,'-- . 



abundant as with 



6. Oscillation of the plane of polarization by the discharge of 

 a battery. — Biciiat and IJi.onoot have studied the effect of a 

 Leyden jar discharge in producing a rotation of the plane of po- 

 larization in a transparent medium. The body is placed between 

 the polarizer :md analyzer, arranged Cor extinction in a bobbin, 

 which is wound round with a long tine wire. A discharge takes 

 place when the difference of potentials is sufficient ; at this instant 

 a bright reappearance of light is seen by the eye situated in trout 

 of the analyzer, showing a rotation of the plane of polarization. 

 A miiTor, rotating on a vertical axis, was now placed before the 

 optica] apparatus: the polarizer was provided with a vertical slit 

 whose image was observed in the rotating mirror by a telescope, 

 the arrangement being such as to cause the appearance of the spark 

 at the right instant. In general, a series of broad luminous bands 

 was observed corresponding to the oscillatory currents of the dis- 

 charge. Further, it was observed that the rotation of the ana- 

 lyzer through a small angle' in one direction caused the even bands 

 to grow weaker and the odd ones to increase, and ric< versa for a 

 rotation in the opposite direction. From this it is concluded that 

 the plane of polarization undergoes successive rotations alternately 

 iu opposite directions, or in other words, it oscillates about its 

 normal position, each oscillatory discharge corresponding to an 



The authors also arranged the apparatus so that there could be 

 seen at once in the rotating mirror, the hands furnished by the 

 light of tin- spark, and those due to the oscillation of the plane of 



is corresponded exactly, so that the two phenomena 

 ered to be simultaneous; no difference in time as : 

 second could be observed. — C. II., June 12, 1882. 



II. Geology and Natural History. 



On the rr/atice n,j, s ,i„d classification of the Pos 



