128 FRAGMENTS OF SCIENCE 



sively diffused the smoke of incense, and tobacco -smoke. 

 His first brief communication stated the fact of polariza- 

 tion by such smoke; but in his second communication he 

 announced the discovery of a neutral point in the beam, 

 at the opposite sides of which the light was polarized in 

 planes at right angles to each other. 



But unlike my observations on the laboratory air, and 

 unlike the action of the sky, the direction of maximum 

 polarization in M. Grovi's experiment enclosed a very 

 small angle with the axis of the illuminating beam. The 

 question was left in this condition, and I am not aware 

 that M. Govi or any other investigator has pursued it 

 further. 



I had noticed, as before stated, that as the clouds 

 formed in the experimental tube became denser, the po- 

 larization of the light discharged at right angles to the 

 beam became weaker, the direction of maximum polariza- 

 tion becoming oblique to the beam. Experiments on the 

 fumes of chloride of ammonium gave me also reason to 

 suspect that the position of the neutral point was not 

 constant, but that it varied with the density of the illumi- 

 nated fumes. 



The examination of these questions led to the follow- 

 ing new and remarkable results: The laboratory being 

 well filled with the fumes of incense, and sufficient time 

 being allowed for their uniform diffusion, the electric 

 beam was sent through the smoke. From the track of 

 the beam polarized light was discharged; but the direc- 

 tion of maximum polarization, instead of being perpen- 

 dicular, now enclosed an angle of only 12 or 13 with the 

 axis of the beam. 



A neutral point, with complementary effects at oppo- 



