NATURAL SOURCES OF POLARIZED LIGHT. 



BY C. ^^. BROOM ALL. 



Few people realize what a common phenomenon polarized 

 litrht is in nature. Indeed, as regards reflected light, it may 

 be said that unpolarized rays are the exception rather than 

 the rule. In this connection the following simple experiments 

 concerning facts familiar to every student of physics may be 

 of sufficient general interest to mention. 



On the occasion of a recent quite vivid rainbow display, 

 the writer was afforded a particularly good opportunity, with 

 very simple apparatus, to demonstrate the fact that the light 

 from the rainbow is polarized. It was found by experiment- 

 ing with a Xichol prism held in the hand between the eye and 

 the rainbow that all the colors of the spectrum were strongly 

 polarized. When the prism was held in one certain position 

 the rainbow would be plainly visible, while when the Xichol 

 was rotated ninety degrees the colors disappeared. It impressed 

 one as almost magical to see this great band of color com- 

 pletely obliterated by the simple rotation of a transparent 

 body. A piece of mica, which happened to be handy, was 

 then interposed between the Xichol and the rainbow, and it 

 was found that, when the mica was held at the proper angle, it 

 had the power to bring V)ack again into view the rainbow pre- 

 viously made invisible by the prism. If the Xichol was now 

 rotated ninety degrees, all portions of the rainbow became 

 visible again, except the portion shielded by the piece of mica. 

 In other words, the mica, if properly oriented, made the rain- 

 bow invisible to the eye when the Xichol was in such a posi- 

 tion as to allow the colors to be clearly seen, while when the 

 prism was in such a position as to hide the bow the mica 

 brought it plainly into view. It was a very interesting sight 

 U) view the leaden sky through the prism and then restore the 

 beautiful colors of the rainbow b.y the interposition of a piece 

 of^cirdinary mica. As was to be expected, the thickness of the 

 mica wns of considerable ini]~)ortance, as certain portions of it 



