Intelligence and Miscellaneous Articles. 157 
Mr. Forbes has brought a “Devonian” trilobite (Phacops latifrons 
or Ph, Bufo), in a rolled pebble, from Oruro: it is a widely-spread 
species. Another allied form was found by Mr. Pentland, many 
years back, at Aygatchi. In other respects the “ Devonian” evidence 
is scanty. 
In Mr. Forbes’s fine collection of Silurian fossils none of D’Or- 
bigny’s ten Silurian species occur ; nearly all are such as are met 
with in Lower Devonian and in Upper Silurian rocks—Homalonotus, 
Tentaculites, Orthis, Ctenodonta, Pileopsis (2), Strophomena, Bellero- 
phon. South Africa and the Falkland Isles yield a similar fossil 
fauna. 
The Bilobites in this collection differ, some of them probably ge- 
nerically, from D’Orbigny’s figured species. A little Beyrichia from 
the upper part of the Silurian series in Bolivia appears to be like a 
North American form figured by Emmons as Silurian. 
XXIV. Intelligence and Miscellaneous Articles. 
ON THE POLARIZATION OF LIGHT BY DIFFUSION. BY G. GOVI, 
oe polarization of atmospheric light has long since proved that 
gases, as well as solid and liquid bodies, have the property of 
_ polarizing light; but I am not aware that any direct experiments 
have been made to prove the presence of polarizing power in the 
case of gases. 
I was led to the consideration of this question by the polariscopic 
study of the hght of comets; and the idea occurred to me to inves- 
tigate how a pencil of light would be affected by being transmitted 
through a certain thickness of a gaseous medium in which it was re- 
flected or diffused. 
The experiment was made in the following manner:—A thick 
pencil of the sun’s rays, reflected from a heliostat, was allowed to 
pass into a dark room, through a hole in the window-shutter. ‘This 
light was principally reflected from metal, and showed very feeble 
traces of polarization. A large quantity of smoke was then pro- 
duced by burning incense ; and the pencil immediately expanded and 
formed a large cylinder, which diffused white light in all directions. 
This light, when investigated by a polariscope, was found to be po- 
larized even when the cylinder was viewed at right angles to its 
axis; but the intensity of the polarization was truly extraordinary 
when the direction of the visual ray, on the side of the source of light, 
formed a somewhat small angle with the axis of the cylinder: one 
would have said that the phenomenon was caused by the action of 
a solid or liquid body on the molecules of the ether. Viewing the 
cylinder in this direction, the polarization perceptibly decreased on 
approaching the source of light or removing from it. The light pro- 
ceeding from the column of smoke seen by reflexion upon the 
aperture was only feebly polarized. 
Iixcepting in its intensity, the above phenomenon presents nothing 
extraordinary; but for a physicist the circumstance appears to me 
important, that the light polarized by diffusion does not seem to arise 
from a simple reflexion from gas moiecules, for its plane of polar- 
