120 
MRS. SOMERVILLE ON THE ACTION OF RAYS. 
paler surface, and in the centre of which a very dark oblong - spot appeared ; thus from 
the exterior lilac ground on each side of the image to the central spot, there were 
five changes of intensity and tint, reckoning the central spot, but not the lilac ground ; 
and though several of these were mere lines, the whole figure was considerably larger 
than the visible spectrum (fig. 21.). Another remarkable instance occurred, both of 
these bands and of the breadth of the image, when paper coated with white nitrate of 
silver was washed with the milky juice of the fig-tree in alcohol, exposed wet to the 
spectrum. The first effect was a fine clear brown image, beginning with a curve at 
the orange, and extending far beyond the violet rays, within which an olive-green 
centre began to appear under the green rays, which by degrees extended to the end 
of the violet. The brown edges bordering the olive-green were strongly marked, 
and seemed to spread beyond the sides of the visible spectrum throughout the violet, 
indigo, blue and green, but were united by a very black round spot under the yellow, 
and this spot was inclosed on the under side by a brick-red cusp stretching up on 
each side beyond the orange rays, at the lower end of which was a circular spot of 
very pale yellowish-white ; the whole figure was surrounded by a broad reddish border, 
and after long exposure the centre of the green assumed a dark greyish hue, so that 
there were various tints, estimating laterally from the ground to the centre of the 
figure (fig. 22.). 
Juice of the dark purple flower of a kind of mint in alcohol afforded another in- 
stance of several bands. The liquid gave the paper a brownish tint, on which the 
spectrum impressed a long dark line about the breadth of a common pin, cut off by 
the orange rays, but reaching to the end of the violet. On being again washed with 
the juice, the dark brown line gradually increased in width, taking a curved termina- 
tion in the yellow', where it was broadest and tapering upwards ; the interior after- 
wards assumed a pale hue, leaving a dark margin ; the whole at last was surrounded 
by a pale border bounded by a very dark line, which were barely visible next day. 
Two insulated dark spots were distinctly marked below the image. 
These out of many instances are sufficient to show the peculiar appearance alluded 
to, which it is difficult to account for, unless that at each successive washing the heat 
of the spectrum, by drying the parts immediately around it more rapidly than the 
rest of the surface, may thus produce the various borders, and extend the figure be- 
yond its visible edges; however, some of the other phenomena could not be so ex- 
plained, and possibly may have been connected with the action of the atmospheres of 
the sun or earth, as you have remarked, or to a difference in the action of the rays at 
the edges of the sun’s disc from those in its centre. I fear I may have made some 
mistakes, especially in the estimation of the action of the different coloured rays, the 
limits of which it was extremely difficult to determine in so small a spectrum as that 
with which I worked. 
