114 
MRS. SOMERVILLE ON THE ACTION OF RAYS 
quently the extensive pale figure was obliterated, leaving only the interior dark image 
with its halo and the spots with their disc permanent. 
The juice of beet-root in a strong solution of common salt imparted a pink colour 
to the paper, and the most refrangible rays acquired a powerful bleaching energy. 
The pink ground was whitened under the lavender, indigo and blue ; a deep crimson 
spot was formed under the yellow, with a rose-coloured halo elongated to the bleached 
part on one side, and to the end of the orange on the other, while a hazy rose-coloured 
disc was visible at a distance below the red (fig. 6.). The crystallization of the salt 
on this figure was in proportion to the intensity of colour; most on the crimson spot 
and its halo and on the coloured disc, but scarcely any on the bleached portion. 
A solution of hyposulphate* of potash in the beet-juice had nearly the same effect 
as the salt, only that the dark spot with its halo was more extended, and the latter 
formed a long neck beyond the red, ending in a deep rose-coloured disc. The ap- 
pearance was precisely similar when muriate of ammonia or iodide of potassium was 
used, I therefore inferred that the alkali imparted the bleaching property to the most 
refrangible rays. 
Paper washed with the juice of beet-root in distilled water assumed a fine rose- 
colour, on which a figure was bleached by the spectrum, wide and rounded in the 
yellow, but tapering upwards: after another wash, a dark crimson image was formed 
in its centre reaching to the blue, with a still darker spot under the yellow. The red 
rays had no effect, below which at the usual distance two indistinct spots appeared. 
A drop of sulphuric acid in the juice changed the tint of the paper to a purple colour, 
on which, after various alternations of bleaching and darkening, the spectrum im- 
pressed a dark figure, broad and rounded on the yellow, and tapering to the blue, 
beyond which there was scarcely any action (fig. 8.). The whole was surrounded by 
a broad pale border, stretching in a neck far beyond the red, with an indefinite dark 
line in its centre. 
In these experiments almost the only part of the visible spectrum that darkened 
the surface was that of mean refrangibility, but even when the whole had that effect, 
the maximum was generally produced by the rays in question, the insulated spots, or 
some indication of them, appearing at the same time. This was the case with the 
juice of AmarantJms caudat.a, which stained white paper rose-colour, and the spectrum 
impressed a deeper rose-coloured image from the lowest edge of the red to the end 
of the blue, with a dark crimson oval figure under the yellow and green, while two 
insulated crimson spots appeared in a rose-coloured halo below. 
White paper washed with the juice of rose-coloured verbena in distilled water 
assumed a lemon-colour (fig. 9.), while the spectrum impressed a pale rose-coloured 
image from the lowest edge of the red to the end of the indigo rays, in the centre of 
* Sic in MS. but probably meaning hyposulphite, a salt in common use in photographic research, which the 
hyposulphate is not. The two salts have totally different properties. The mistake is a very common one. — 
(J. F. W. H.) 
