connected with the Polarization of Light. 441 
shaded from the direct rays by means of a small screen, the 
striated band will appear illuminated throughout the entire are, 
and the reflected light may be observed directly by means of an 
analyser, which causes it to appear alternately more or less bright. 
The polarization thus produced does not seem to depend on 
the nature of the metal of which the plate is formed. Gold, 
platinum, copper, steel, brass, speculum metal, aluminium, tin, 
&c., have been substituted for silver; and all these metals, when 
suitably striated, have presented the same phenomena without 
sensible difference, except with regard to the colour of the light 
polarized by reflexion. 
Metals which themselves possess least colour, give reflexions 
tinged with yellow, which, when most oblique, become bronze ; 
while in the case of metals that have a marked colour of their 
own, the reflexions possess the same tinge, and sometimes,-indeed, 
in a striking degree, as 1s the case with copper and gold. 
I should mention here that the striated bands on silver and 
copper and some other metals are very brilliant when they have 
recently been made, but that they diminish in intensity on 
account of the action of the vapours accidentally present in the 
atmosphere. Gold and platinum are of course exempt from this 
inconvenience. 
Non-metallic substances present similar phenomena, but 
their reflexions are so dull that the observation is often un- 
certain. Polarization parallel to the lines has nevertheless been 
clearly observed with a plate of specular iron and with one of 
obsidian, both of which I owe to the kindness of M. de Senar- 
mont. With some precautions the phenomenon may even be 
observed with a plate of glass. 
Finally, the groups of lines on silver and copper surfaces have 
been moulded with black wax, gum-lac, and even with galvanic 
copper; and the impressions so obtained presented to all appear- 
ance the same phenomena as the surface actually furrowed. 
Among the various experiments that were tried, I may men- 
tion the case of a scratched metal surface which at first gave a 
reflexion distinctly polarized parallel to the lines, but which was 
afterwards covered with varnish. Under these circumstances the 
polarization became hardly sensible—a result which seems most 
naturally explicable on the ground of the change of the direction 
of the rays owing to the refraction of the varnish, which pre- 
vented the incident light from impinging at that angle which is 
required to produce the polarization in question. In fact, when 
glass plates differently cut were fastened to the striated plate by 
means of a varnish of turpentine or Canada balsam, the polar- 
ization was immediately reproduced in the refracting substance 
whenever the direction of the ray was such that the phenomenon 
