﻿1108 



Prof. P. "W. Wood on Polarized 



of the two spectra. Figure 1 shows the arrangement of the 

 apparatus. 



A is a quartz wedge of small angle cut parallel to the axis. 

 With monochromatic polarized light properly oriented, this 

 shows when viewed through an analyser a fringe system, 

 the visibility of which increases with the percentage of 

 polarization. B is a double-image prism of quartz, C the 

 camera with quartz lens, and D the exhausted tube 

 containing the mercury vapour, a cross-section of the 

 illuminated end of which is shown at E. 



Fio-. l. 



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x 



Photographs of the polarization fringes reproduced as 

 negatives on Plate IX. show clearly that they are distinct 

 quite up to the wall of the tube, where the exciting radiation 

 enters, and that they are of equal visibility all along the 

 column of excited vapour. Photographs were also made 

 through the side of the tube, with the exciting radiation 

 passing down its axis, and similar results obtained. The 

 fringes are more distinct when the opposite ^end of the 

 quartz tube and the contained drop of mercury are cooled 

 with a bath of ice and salt. At room temperature there is 

 much secondary resonance radiation between the primary 

 beam and the observation window, and this undoubtedly 

 reduces the visibility of the fringes. I believe, however, 



