404 THE CANADIAN NATURALIST. [Vol. ix. 



We simply heat the selenium over a gas stove and observe its 

 appearance. When the selenium attains a certain temperature, 

 the beautiful reflectins; surface becomes dimmed. A cloudiness 

 gradually extends over it, somewhat like the film of moisture pro- 

 duced by breathing upon a mirror. This appearance gradually 

 increases, and the whole surfl\ce is soon seen to be in the metallic, 

 granular or crystalline condition. The cell may then be taken off 

 the stove and cooled in any suitable way. When the heating 

 process is carried too far, the crystalline selenium is seen to melt. 

 Our best results have been obtained by heating the selenium until 

 it crystallizes, and continuing the heating until signs of melting 

 appear, when the gas is immediately put out. The portions that 

 had melted instantly re-crystallize, and the selenium is found 

 upon cooling to be a conductor, and to be sensitive to light. The 

 whole operation occupies only a few minutes. This method has 

 not only the advantage of being expeditious, but it proves that 

 many of the accepted theories on this subject are falhicious. Our 

 new method shows that fusion is unnecessary, that conductivity 

 and sensitiveness can be produced without long heatinz and slow 

 cooling; and that crystallization takes place during the heating 

 process. We have found that on removing the source of heat 

 immediately on the appearance of the cloudiness, distinct and 

 separate crystals can be observed under the microscope, which 

 appear like leaden snow-flakes on a ground of ruby red. Upon 

 removing the heat when crystallization's further advanced, we 

 perceive under the microscope masses of these crystals arranged 

 like basaltic columns standing detached from one another, and at 

 a still higher point of heating the distinct columns are no longer 

 traceable, but the whole mass resembles metallic pudding-stone, 

 with here and there a separate snow-flake, like a fossil, on the 

 surface. Selenium crystals formed during slow cooling after 

 fusion present an entirely different appearance, showing distinct 

 facets. 



We have devised about fifty forms of apparatus for varying a 

 beam of light in the manner required, but only a few typical vari- 

 eties need be shown. The source of light may be controlled or 

 a steady beam may be modified at any point in its path. The 

 beam may be controlled in many ways. For instance, it may be 

 polarized, and then affected by electrical or magnetic influences in 

 the manner discovered by Faraday and Dr. Ker. The beam of 

 polarized light, instead of being passed through a liquid may be 



