Intelligence and Miscellaneous Articles. 79 



OX THE OSCILLATIONS OF THE PLANE OF POLARIZATION PRO- 

 DUCED BY THE DISCHARGE OF A BATTERY : SIMULTANEITY OF 

 THE ELECTRICAL AND OPTICAL PHENOMENA. BY D. BICHAT 

 AND R. BLONDLOT. 



We proposed to ourselves to study the rotation of the plane of 

 polarization in a transparent body under the action of the current 

 from the discharge of a Leyden jar. The experiment was arranged 

 as follows. 



Between a polarizer and an analyzer at extinction the transpa- 

 rent body is placed in a bobbin with a long and fine wire which is 

 connected with the armatures of a battery. An exciter interca- 

 lated in the circuit permits the discharge to be produced when the 

 difference of potential is sufficient. At the instant of each dis- 

 charge the eye, placed in front of the analyzer, perceives a vivid 

 reappearance of light, which shows that the plane of polarization 

 has been deflected. 



This fact having been proved, we sought to analyze it. For that 

 purpose we placed before the optical apparatus a mirror rotating 

 about a vertical axis. The polarizer was furnished with a slit, like- 

 wise vertical, the image of which was observed in the mirror by 

 means of a telescope. By a suitable arrangement we compelled 

 the spark to burst forth at the moment when the mirror, in its con- 

 tinuous rotation, occupied such a position that the image of the 

 slit was visible in the telescope. We thus saw in the rotating 

 mirror the reappearance of light clue to each discharge. 



What we observed was this : — In general, in the field of the 

 telescope a series of broad luminous bands are seen, separated by 

 narrower dark bands. The appearance reminds one absolutely of 

 that which is observed when the light of the spark is examined. 

 It is known that in that case the successive luminous bands corre- 

 spond to currents alternately in opposite directions : the discharge 

 is oscillatory. We have ascertained that it is the same with the 

 plane of polarization. In fact, if the analyzer be rotated a small 

 angle in a certain direction, the images of the even order are seen 

 to be weakened, and at the same time the images of the odd order 

 to increase in brightness. If the rotation take place in the oppo- 

 site direction, the images of the odd order are weakened, and those 

 of the even order become brighter. 



The plane of polarization, then, undergoes successive rotations 

 alternately in opposite directions ; it oscillates about its normal 

 position. To each oscillatory discharge corresponds an oscillatory 

 movement of the plane of polarization. 



This being admitted, is there simultaneity between the electric 

 and optic phenomena? or does the movement of the plane of po- 

 larization manifest itself in an appreciable time after the electric 

 action '? We have solved this question in the following manner : — 

 To the apparatus employed for the preceding experiments we added 

 an arrangement permitting to be seen at the same time, in the 

 rotating mirror, the bands furnished by the light of the spark and 

 those due to the oscillation of the plane of polarization. For this 



