Action of the Rays of the Solar Spectrum on Vegetable Colours. 5 
ceedingly striking, by discharging the steam obliquely as in 
fig. 5, in which case the’ ball will take up its position at a 
greater distance from the orifice, but will still be sustained in 
the current, notwithstanding that gravity in this instance acts 
at an angle to the jet. A hollow globe made of thin brass or 
copper and from two to three inches in diameter, answers very 
well for the purpose, where the steam is discharged from an 
aperture not less than !,th of a square inch in area. 
In the well-known experiment of supporting a ball upon the 
summit of a jet of water, the ball merely reposes in the hollow 
formed by the liquid in the act of turning over to fall to the 
ground, which is very different from being sustained in the 
current as it is in the case of the steam. 
Jesmond Dene, Newcastle-upon-Tyne, WM. Gero. ARMSTRONG. 
Noy. 15, 1842. 
II. On the Action of the Rays of the Solar Spectrum on Vege- 
table Colours, and on some new Photographic Processes. By 
Sir Joun F. W. Herscuen, Bart., K.H., F.R.S.* 
[With a Plate.] 
149+. IX my paper on the “‘ Chemical Action of the Solar 
Spectrum on preparations of Silver and other sub- 
stances,” read to the Royal Society in February 1840, and of 
which the present communication is intended as a continua- 
tion or supplement, some experiments on the effect of the 
spectrum on the colouring matter of the Viola tricolor, and 
on the resin of guaiacum are described, which the extreme 
deficiency of sunshine during the summer and autumn of the 
year 1839 prevented me from prosecuting efficiently up to the 
date of that communication. The ensuing year 1840 was 
quite as remarkable for an excess of sunshine as its predeces- 
sor for the reverse. Unfortunately the derangements conse- 
quent on a change of residence prevented my availing myself 
of that most favourable conjuncture, and it was not till the 
autumn of that year that the inquiry could be resumed. From 
that time to the present date it has been prosecuted at inter- 
vals as the weather would allow, though owing to the almost 
unprecedented continuance. of bad weather during the 
whole of the past summer and autumn (1841), it has of 
late been almost wholly suspended ¢. In photographic pro- 
cesses, where silver and other metals are used, the effect of 
* From the Philosophical Transactions, 1842, p. 181; having been re- 
ceived by the Royal Society June 15, and read June 16, 1842. 
+ The paragraphs, for convenience of reference, are numbered in con- 
tinuation of those of the previous paper referred to in the text [an abstract 
of which will be found in Phil. Mag. S. 3, vol. xvi. p. 331.—Enrr.]. 
{ This was written in April 1842, since which a repetition of the season 
of 1840 seems to have commenced. 
