JUNE. 
131 
could in our experimental hothouse submit 
vegetation to a continued light. * 
A building such as I propose would allow 
of light being- passed through coloured 
glasses or coloured solutions, and so prove 
the effect of the different visible or invisible 
rays which enter into the composition of sun¬ 
light. 'For the sake of exactness nothing is 
superior to the decomposition of the lumin¬ 
ous rays by a prism, and the fixing the rays 
by means of a heliostat. Nevertheless, a 
judicious selection of colouring- matters, and a 
logical method of performing our experi¬ 
ments, will lead to good results. I will give 
as proof, that the recent most careful experi¬ 
ments concerning the action of various rays 
upon the production of oxygen by leaves, and 
upon the production of the green colouring 
matter, have only confirmed the discoveries 
made in 1836, without either prism or helio¬ 
stat, by Professor Daubeny, f from which it 
appears that the most luminous rays have the 
most power, next to them the hottest rays, 
and lastly those called chemical. 
Dr. Gardner in 1843, Mr. Draper imme¬ 
diately after, and Dr. C. M. Guillemin in 
1857,1 corroborated by means of the prism 
and the heliostat the discovery of Dr. Dau- 
beny, which negatived the opinions preva¬ 
lent since the time of Senebier and Tessier, 
and which were the result of erroneous ex¬ 
periments. It was difficult to believe that 
the most refrangible rays—violet for in¬ 
stance, which acts the most on metallic 
bodies—as in photometrical operations, should 
be precisely those which have least effect in 
decomposing the carbonic acid gas in plants, 
and have the least effect over the green 
matter in leaves. Notwithstanding the con¬ 
firmation of all the experiments made by Dr. 
Daubeny, when repeated by numerous phy¬ 
sicists and by more accurate methods, the old 
opinions, appearing more probable, still in¬ 
fluenced many minds ,§ till Mr. Julius Sachs, 
* The apparatus which, produces the most per¬ 
sistent and vivid light is the magneto-electric ma¬ 
chine, based on the development of induction by 
magnetism,as discovered by the illustrious Faraday. 
The galvanic pile is replaced by a steam-engine of 
low power, which sets in motion a wheel furnished 
with magnets (“Bibl. Univ. de Geneve, Archives 
Scientif., 1881, v. 10, p. 160.”). The working of this 
machine is inexpensive; but unfortunately, the 
magnets are very costly. This system has already 
been applied to two lighthouses—that at the South 
Foreland, and to that of the “ Societe 1’Alliance,” at 
Havre — in consequence of the experiments of MM. 
E. Becquerel and Tresca. 
f Daubeny, “ Philos. Trans.,” 1836,part 1. 
' t Dr. Gardner, “ Edinb. |Phil. Mag.,” 1844, extract 
in French in “La Biblioth. Univ. de Geneve,” 
February, 1844; Draper, “Edinb. Phil. Mag.,"Sep¬ 
tember, 1844, extract ib., 1844, vol. 54; Guillemin. 
(C. M.), “Ann. Sc. Nat.,” 1857, ser. 4, vol. 7,p. 154. 
J As a proof of the persistence of the old opinion, 
I will quote a phrase of Professor Tyndall’s in hia 
most clear and interesting treatise “ On Radiation,” 
(London, 1865), p. 6:—“In consequence of their 
chemical energy, these ultra-violet rays are of the 
utmost importance to the organic world.” I do not 
know whether the author had in view the influence 
in a series of very important experiments 
again affirmed tbe truth.* It is really the 
yellow and orange rays that have the most 
power, and the blue and violet rays the least, 
in the phenomena of vegetable chemistry; 
contrary to that which occurs in mineral 
chemistry, at least in the case of chloride of 
silver. The least refrangible rays, such as 
orange and yellow, have also the twofold and 
contrary property, such as pertains also to 
white light, and which produces the green 
colouring matter of leaves or bleaches them, 
according to its intensity. It is these, also, 
which change the colouring matter of flowers 
when it has been dissolved in water or alco- 
hol.f Those rays called chemical, such as 
violet, and the invisible rays beyond violet, 
according to recent experiments, confirmatory 
of those of ancient authors—those of Sebastian 
Poggioli, in 1817, and of C. M. Guillemin—• 
have but one single well-ascertained effect, 
that of favouring the bending of the stem 
towards the quarter from which they come 
more decidedly than do other rays ; yet that 
is an effect perhaps more negative than posi¬ 
tive, if the flexure proceeds, as many still be¬ 
lieve, from what is going on on the side least 
exposed to the light. J 
The effect upon vegetation of the non- 
visible calorific rays at the other extremity 
of the spectrum have been but little studied. 
According to the experiments we have on this 
subject, they would appear to have but little 
power over any of the functions; but it would 
be worth while to investigate further the 
calorific regions of the spectrum by employing 
Dr. Tyndall’s process—that is, by means of 
iodine dissolved in bisulphide of carbon, which 
permits no trace of visible light to pass. 
How interesting- it would be to make all 
these laboratory experiments on a large scale! 
Instead of looking into small cases, or into a 
small apparatus held in the hand, and in 
which the plants cannot be well seen, the 
observer would himself be inside the appa¬ 
ratus, and could arrange the plants as de¬ 
sired. He might observe several species at 
the same time, plants of all habits, climbing 
plants, sensitive plants, those with coloured 
of the chemical rays over the animal kingdom; but 
according to certain passages of Mr. Sachs, I doubt 
if they have more power over animals than they have 
over plants; but Professor Tyndall did not concern 
himself with these questions, he was content to. ex¬ 
plain admirably the physical nature of the various 
rays. 
* The researches of Mr. Sachs first appeared in the 
“Botanische Zeitung ; ” they are collected and con¬ 
densed in the remarkable volume called “ Handbuch 
der Physiologischen Botanik,” vol. 4, Leipsig, 1855, 
p. 1 to 46. 
+ Sir John Herschell, “ Edinb. Philos. Journ.,” 
January, 1843. 
t The rather confused and questionable explana¬ 
tions, founded on the notions of Dutrochet, of the 
existence of a deoxidising power on the brightest 
side, clash with the fact that the blue, indigo, and 
violet rays, the least powerful for deoxidising tissues, 
are the most powerful in causing them to bend. 
