116 
MRS. SOMERVILLE ON THE ACTION OF RAYS 
disc of the same colour as the border appeared below the red, which vanished the 
following' day. 
When the juice was extracted in alcohol instead of water, the action of the spec- 
trum was somewhat different ; the image extended from the lowest edge of the yellow 
to the end of the violet with three points of maximum intensity, the greatest in the 
yellow, the next in the green, and the last in the indigo. The red rays had no effect, 
but the spots, or rather their place was indicated. With water containing a little 
borax, there were only two points of greatest intensity, the first on the yellow, the 
other under the indigo and violet. Notwithstanding these differences the principal 
action was still in the rays of mean refrangibility, especially the yellow. 
I have found no vegetable juice so sensible to light as that of the maroon-coloured 
or dark red dahlia in distilled water. It gave a lavender hue to white paper, while 
the part under a condensed spectrum became rapidly dark, from the edge of the 
orange to the end of the lavender rays, but with variable colour and intensity. A 
dark reddish oval was formed under the orange, yellow and green rays, with a narrow 
line of a still deeper colour in the centre of the yellow, while spots of less intensity and 
of a bluer tint appeared under the blue and violet rays, with some indication of 
another above ; but these three points of inferior intensity were not always very di- 
stinct. At a little distance below the extreme red rays, two dark spots were formed 
in the centre of a hazy disc of reddish purple. A hot iron behind the paper occa- 
sioned no change in the figure, though it accelerated the action and increased its 
sharpness. In this and various other instances I found that repeated washing with 
diluted juice answered better than when it had a deeper colour (fig. 14.). 
The addition of a little sulphuric acid to this juice accelerated the action of the 
rays of mean refrangibility, increased the intensity and breadth of the image, and 
changed the tint of the liquid to bright scarlet, which imparted its hue to white paper. 
Exposed wet to the spectrum a dark red figure by degrees appeared, extending from 
the upper edge of the orange to the end of the violet, in the midst of which a kind 
of oval of great intensity of colour was formed under the yellow and green rays, 
leaving a broad red border around. The red rays seemed to have little or no effect, 
though at some distance below them there were two dark spots on a dark haze. 
When the experiment was repeated with a hot iron behind the paper, the central 
image became almost black, and extended from the lowest edge of the yellow to 
almost the middle of the blue rays, while the dark crimson border passed under the 
orange at one end of the spectrum, ending at the indigo at the other, beyond which 
a pale crimson shade reached certainly to the end of the violet, and probably further, 
but it was so gradually shaded off that it was not possible to define its termination. 
There was a nebulous disc of pale crimson at some distance below the last visible 
red. This image, as well as that in the preceding experiment, were so deeply im- 
pressed that they penetrated the paper (fig. 15.). 
