438 M. H. Fizeau on several Phenomena 
acid and peroxide of lead, fails to yield the characteristic tint if 
nickel be present in large quantity, and the manganese only in 
minute traces: the nickel salt destroys, or at all events modifies 
the colour produced by the formation of permanganic acid. If 
cobalt is present, however, or a solution of a salt of that metal 
is subsequently added, the colour of the nickel is nullified, and 
that of the manganese becomes sensible. 
When red fire, composed of nitrate of strontia, chlorate of 
potash, &c., 1s mixed with green fire containing nitrate of baryta 
and ignited, the red and green rays become invisible, and a white, 
or, rather, a bluish-white flame is produced: the crimson of the 
strontian flame has a dash of blue in its composition, and the 
red being removed by the green, is clearly shown. If a rose-red 
fire be prepared by mixing thirty-four parts of carbonate of lime, 
fifty-two of chlorate of potassa, and fourteen of sulphur, or still 
better, perhaps, twenty-three of dry chloride of calcium, sixty- 
one of chlorate of potassa, and sixteen of sulphur, and then 
ignited with the ordinary green fire, pure white light is produced. 
LXVI. Researches on several Phenomena connected with the Po- 
larization of Light. By M.H. Fizpavu*. 
| i has long been observed that when a ray of light is received 
on a mirror whose surface, instead of being perfectly smooth, 
is scratched with a fine point, it is no longer simply reflected. 
Part indeed follows the ordinary course, but a considerable por- 
tion is dispersed in various directions, some of which deviate 
greatly from that of the regularly reflected ray. We may men- 
tion as an example of this species of phenomenon, the singular 
reflexions produced by surfaces of metal, such as brass and steel, 
&c., which have been artificially prepared by beg rubbed con- 
tinually in one direction with emery, the hard angular particles 
of which produce fine parallel scratches on the surface of the 
metal. The amount of light dispersed by surfaces so prepared, 
in directions other than that of the regularly reflected ray, is cal- 
culated to excite some surprise; and it is generally agreed to 
attribute this effect partly to the variously inclined surfaces of 
the minute furrows with which the mirror is covered, partly to 
the diffraction caused by them in conjunction, acting as an irre- 
gular grating, and producing at the same time, and mingled 
with each other, the phenomena observed by Fraunhofer with 
simple gratings of various structure. 
In studying the light dispersed in this manner with respect to 
* Translated from the Comptes Rendus for February 18, 1861, by F. 
Guthrie. . 
