118 
MRS. SOMERVILLE ON THE ACTION OF RAYS 
The action of the different parts of the spectrum seems very capricious ; for example, 
the most refrangible rays from the green to the end of the lavender darken some 
substances and bleach others. Instances of this bleaching action have been given in 
the juices of Globe amaranthus and Plumbago auriculata, both being bleached to 
whiteness by the rays in question. The red rays occasionally possess this property, 
as in the juice of the Globe amaranthus, those of mean refrangibility more rarely, yet 
an instance has already been given in the case of geranium juice with carbonate of 
soda ; and another occurred when a drop of nitric acid, a little common salt, and sul- 
phate of quinine were mixed with the juice of the dark red dahlia in distilled water. 
White paper repeatedly washed with this liquid acquired a tint of pale lilac, while 
the part under the spectrum was marked by a broad dark crimson image from the 
orange to the end of the violet. After another washing the paper was bleached to a 
very pale yellowish-white under the lavender and violet rays, while at a small interval 
below a second bleaching process began, and changed the interior of the dark image 
to a very pale reddish-yellow down to the beginning of the orange, leaving a dark 
crimson border on each side only, broadest and darkest under the yellow rays, and 
diminishing in width both up and down. Under the orange and red rays the surface 
acquired a pink tinge, and at some distance below, the same pink tinge formed a 
round hazy mark. Although the colours were very tender in this experiment they 
penetrated letter-paper, remaining unchanged many days (fig. 170- 
Singular changes were produced by the spectrum on the juice of the petals of the 
scarlet Zinnia in distilled water, which though not very sensible to the influence of 
light alone, became highly so on the addition of sulphuric acid. White paper washed 
with this liquid acquired a pinkish-grey tint, on which the first effect of the spectrum 
was a very broad dark image under the violet and indigo, with a long narrow appen- 
dage of the same inky tint going down to the end of the red, and also a dark shade 
upwards far beyond the violet. Being again washed with the liquid, the broad image 
under the violet and indigo was bleached white, leaving a dark margin (fig. 18.). 
The dark appendage then gradually became broader, the greatest intensity lying under 
the green and yellow, and a dark disc appeared below the red (fig. 19.). After 
another washing a bleaching action changed all the interior of the dark appendage, 
from the upper edge of the green to the end of the red rays, to a very pale buff co- 
lour : after a while a yellow brown or dark buff image appeared in its interior under 
the orange, yellow and green, leaving a very dark margin ; and now the whole image 
was surrounded by an inky pink-coloured border, much wider than the visible spec- 
trum, extending on a long neck to the dark disc already mentioned, in which the 
uppermost spot was seen, but the whole of the dark border had vanished next day. 
I have not found much variety of colour, although it was occasionally remarkable : 
the juice of the thread-shaped petals of a yellow thistle in distilled w r ater gave a 
bright yellow colour to white paper, on which the spectrum impressed a very long 
narrow image throughout the whole visible rays, varying in colour and intensity. 
