44.2 M. H. Fizeau on several Phenomena: 
would have been produced in the air. It is, however, well known 
that instruments constructed of brass, copper, and bronze, which 
are rendered brilliant by polishing, are generally covered with a 
coat of varnish for the purpose of preserving the brightness of 
the metal, and there is therefore no reason for surprise that the 
reflexions from these metals, however bright they may be, pre- 
sent no sensible polarization. When these surfaces have not 
been varnished, and when, moreover, they have been obtained 
by the action of polishing substances not too coarse, the pheno- 
mena are invariably observed. 
No mention has yet been made of the light regularly reflected 
by a striated surface. In this direction the observation is not 
so easy, because the rays reflected by the furrows mingle with 
those reflected from the smooth surface of the mirror. Neyver- 
theless, on observing with a microscope single lines suitably illu- 
minated, a sensible polarization may be detected which varies 
little with the angle of reflexion; but what is strange is that the 
direction of this polarization is opposite to that which is produced 
in the former case, being perpendicular to the lines on the sur- 
face. The same fact may even be observed on regarding a stri- 
ated surface directly by means of an analyser. In this ease, 
to render the phenomenon sensible, it is sufficient to trace 
two bands of lines at right angles on a silver surface, and to 
observe the reflected rays almost normally, the source of light 
being a white surface equally illuminated. The direction of the 
lines being perpendicular in the two bands, and each band po- 
larizing the light perpendicularly to its direction, it results that 
the two bands give opposite polarizations, and that the phe- 
nomenon becomes more sensible by contrast. 
The same effect may be observed, without much difference, 
whether the incident rays are normal or more or less oblique, the 
reflected rays invariably possessing a partial polarization sensibly 
perpendicular to the direction of the lines. 
This phenomenon is rendered very obvious on striating a space 
of some centimetres diameter on a polished plate by means of a 
lathe ; the portion covered with concentric lines, bemg regarded 
with an analyser, presents two dark tufts similar to the tufts dis- 
covered by M. Haidinger. 
This phenomenon may be rendered still more visible by uni- 
formly furrowing the entire surface of two mirrors, placing them 
parallel and opposite to each other, and causing light to be 
reflected repeatedly from one to the other: at each of these 
reflexions an additional portion of light is polarized; so that 
after several reflexions in a direction which may be as near the 
normal as possible, the polarized light greatly exceeds the non- 
polarized in quantity. 
