Tainter and Bell—Production of Sound by Inght. 317 
We now simply heat the selenium over a gas stove and ob- 
serve its appearance. When the selenium attains a certain 
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 
This method has not only the advantage of being 
expeditious, but it proves that many of the accepted theories on 
this subject are fallacious. . 
Karly experimenters considered that the selenium must be 
‘cooled from a fused condition with extreme slowness.” Later 
authors agree in believing that the retention of a high tempe- 
rature—short of the fusing point—and slow cooling—are essen- 
tial, and the belief is also prevalent that crystallization takes 
place only during the coolin ess. 
ur new method shows that fusion is unnecessary, that con- 
ductivity and sensitiveness can be produced without long heat- 
ing and slow cooling; and that crystallization takes place 
during the heating process. We had found that on removing 
the source of heat, immediately on the appearance of the cloudi- 
ness above referred to, distinct and separate crystals can 
served under the microcsope, which appear like leaden. snow 
flakes on a ground of ruby red. 
Upon removing the heat when crystallization is further ad- 
vanced, we perceive under the microscope masses of these 
crystals arranged like basaltic columns, standing detached 
from one another—and at a still higher temperature the dis- 
tinct columns are no longer traceable, but the whole mass 
resembles metallic pudding-stone with here and there a sepa- 
rate snow flake, like a fossil on the surface. Selenium crystals 
formed during slow cooling after fusion, present an entirely 
different appearance, showing distinct facets. 
must now endeavor to explain the means by which a beam 
of light can be controlled by the voice of a speaker. 
