190 
SIR J. F. W. HERSCHEL ON THE ACTION OF THE RAYS 
ticed in Chryseis californica , the earliest flowers of which exhibited in the photo- 
graph of their spectrum a well-insulated round spot, eaten away by red rays almost 
at its extremity, which spot I never was able to reproduce with later flowers from 
the same root. Those gathered at the end of its flowering also left a residual yellow 
of extreme obstinacy*, which was by no means the case with the earlier flowers. 
174. It would be waste of time to enumerate all the vegetable tints which I have 
subjected to experiment, comprising most of the ordinary hardy garden and wild 
flowers of the country. To the rarer and more splendid species which adorn the 
stoves and greenhouses of florists, I have had little access, a circumstance I much 
regret, and which leads me to take this opportunity of mentioning, that specimens of 
paper stained with the juices of highly-coloured, or otherwise remarkable flowers or 
leaves, either by alcoholic extraction, or by simple expression (if accompanied with 
the botanical name of the plant used), will be highly acceptable, from whatever 
quarter received. I shall here set down only those which afforded some ground for 
special remark, so far as I have yet pushed the inquiry. 
Colours of particular Flowers. 
17 5. Corchorus Japonica. — The flowers of this common and hardy but highly or- 
namental plant, are of a fine yellow, somewhat inclining to orange, and this is also 
the colour the expressed juice imparts to paper. As the flower begins to fade the 
petals whiten, an indication of their photographic sensibility, which is amply verified on 
exposure of the stained paper to sunshine. I have hitherto met with no vegetable 
colour so sensitive. If the flowers be gathered in the height of their season, paper so 
coloured (which is of a very even and beautiful yellow) begins to discolour in ten or 
twelve minutes in clear sunshine, and in half an hour is completely whitened. The 
colour seems to resist the first impression of the light, as if by some remains of vi- 
tality, which being overcome, the tint gives way at once, and the discoloration when 
commenced goes on rapidly. It does not even cease in the dark when once begun. 
Hence it happens that photographic impressions taken on such paper, which when 
fresh are very sharp and beautiful, fade by keeping, visibly from day to day, however 
carefully preserved from light. Specimens of such photographs (copies of engravings) 
are submitted with this paper for inspection. They require from half an hour to an 
hour to complete, according to the sunshine. Hydriodate of potash cautiously ap- 
plied, retards considerably, but does not ultimately prevent, this spontaneous dis- 
charge. 
176. Exposed to the spectrum, in about fifteen or twenty minutes the colour is 
totally destroyed and the paper whitened in the whole region of the green, blue and 
violet rays, to which therefore the most energetic action is confined, agreeably to the 
law of complementary tints (Art. 170.). If the action of the spectrum be prolonged, 
* Probably, therefore, useful in dyeing. The species is that most commonly cultivated in gardens, with 
bright yellow petals having orange-coloured bases. 
