Solar rays bleach dead vegetable matter with rapidity, while in living
parts of plants their action is frequently to strengthen the colour.
Their power is perhaps best seen on the sides of peaches, apples, &c.,
which, exposed to a midsummer’s sun, become highly coloured. In the
open winter of 1850, Mr. Adie, of Liverpool, found in a wallflower
plant proof of a like effect: in the dark months there was a slow
succession of one or two flowers, of uniform pale yellow hue; in March
streaks of a darker colour appeared on the flowers, and continued to
slowly increase till in April they were variegated brown and yellow,
of rich strong colours. On the supposition that these changes are
referable to magnetic properties, may hereafter be explained Mrs.
Somerville’s experiments on steel needles exposed to the sun’s rays
under envelopes of silk of various colours; the magnetisation of steel
needles has failed in the coloured rays of the spectrum, but Mr. Adie
considers that under dyed silk the effect will hinge on the chemical
change wrought in the silk and its dye by the solar rays.