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XXXIV. On the Photographic Transparency of various Bodies, and on the Photographic 
Effects of Metallic and other Spectra obtained by means of the Electric Spark. 
By W. A. Millee, M.B., LL.B., Treas. & V.P.B.S., Professor of Chemistry in 
King's College, London. 
Eeceived June 19, — Read June 19, 1862. 
1. At the Meeting of the British Association held in Manchester last autumn, I exhi- 
bited some photographs of spectra from the electric spark obtained between wires of 
different metals by means of an induction-coil. Upon this occasion a hollow prism filled 
with bisulphide of carbon was employed, because, owing to its great dispersive power, 
it furnished spectra in which the lines under examination were more widely separated 
and exhibited with greater distinctness than by any other medium in ordinary use. 
Plate XXXIX. fig. 30 exhibits a copy of the photograph of the solar spectrum obtained 
by means of a hollow glass prism filled with bisulphide of carbon, contrasted with the 
spectrum obtained through the same prism simultaneously from the spark between 
copper terminals of the secondary coil in the induction apparatus. In this, and in all 
the subsequent figures, the less refrangible end of the spectrum is upon the left-hand 
side of the Plate. 
The great prolongation of the more refrangible portion of the spectrum beyond the 
part risible to the unaided eye, led me to believe that the bisulphide was a material 
which exerted but little absorbent action upon the chemical rays. Subsequent experi- 
ments have, however, convinced me that this opinion was erroneous, and have rendered 
it necessary to modify considerably the conclusions deduced from those experiments. 
2. At the time that that paper was written, I believed that the photographic effects 
produced by the electric spectra of all the metals furnished results in a great degree 
similar to each other, if not actually identical. This, it will be seen from subsequent 
statements, is correct so far as the fact of the similarity in this portion of the spectra is 
concerned, but is erroneous as regards the general conclusion deduced from it. During 
the past winter I have renewed these experiments, substituting a quartz-train for glass 
and bisulphide of carbon, and have chiefly used a fine quartz prism, kindly lent to me by 
my friend Mr. Gassiot. The refracting-angle of this prism is about 60°; its faces are 
about 2 inches long and I|- inch broad, and are so cut as to furnish a singly refracted 
beam for the medium rays, by transmitting it along the axis of the crystal. It is well 
known, from the experiments of Prof Stokes* and M.E.Becqueeel, that quartz is remark- 
able for its transparency to both fluorescent and phosphorogenic rays of high refrangibility. 
* Phil. Traus. 1852, p. 540. 
6 B 
MDCCCLXII. 
