NEW CHEMICAL REACTIONS. 



91 



neutral point to the observer's eye measured in the first 

 instance 66 degrees. 



The windows of the laboratory were now opened for 

 some minutes, a portion of the incense-smoke being per- 

 mitted to escape. On again darkening the room and turn- 

 ing on the light, the line of vision to the neutral point was 

 found to enclose, with the axis of the beam, an angle of 63 

 degrees. 



The windows were again opened for a few minutes, more 

 of the smoke being permitted to escape. Measured as be- 

 fore, the angle referred to was found to be 54 degrees. 



This process was repeated three additional times; the 

 neutral point was found to recede lower and lower down 

 the beam, the angle between a line drawn from the eye to 

 the neutral point and the axis of the beam falling succes- 

 sively from 54 degrees to 49 degreees, 43 degrees and 33 

 degrees. 



The distances, roughly measured, of the neutral point from 

 the lamp, corresponding to the foregoing series of observa- 

 tions, were these: 



1st observation 



2d 



3d 



4th 



5th 



6th 



2 feet 2 inches. 



6 



10 

 2 

 7 

 6 



At the end of this series of experiments the direction of 

 maximum polarization had again become normal to the 

 beam. 



The laboratory was next filled with the fumes of gun- 

 powder. In five successive experiments, corresponding to 

 five different densities of the gnnpowder-srnoke, the angles 

 enclosed between the line of vision to the neutral point and 

 the axis of the beam, were 63 degrees, 50 degrees, 47 de- 

 grees, 42 degrees, and 38 degrees respectively. 



After the clouds of gunpowder had cleared away, the 

 laboratory was filled with the fumes of common resin, ren- 

 dered so dense as to be very irritating to the lungs. The 

 direction of maximum polarization enclosed, in this case, 

 an angle of 12 degrees, or thereabouts, with the axis of the 

 beam. Looked at, as in the former instances, from a 



