es es 
Fuly 17, 1873] 
the close of their studies with certificates testifying to 
their diligence and their acquirements. 
All this instruction is absolutely gratuitous. M. Fremy 
wishes to remain faithful to the old motto of the museurn, 
“Tout est gratuit dans l’établissement,” though this ex- 
cessive liberality is perhaps open to criticism. 
Behind the magnificent chemical rooms we found the 
modest laboratory of M. Decaisne. Descending a few 
steps we reach a garden set apart to experiments in 
culture, having on the left a glazed gallery: this is the 
laboratory of vegetable anatomy and physiology. M. 
Decaisne superintends and advises the anatomists during 
his daily visits ; M. Dehérain, who is well known for his 
researches in agricultural chemistry and vegetable phy- 
siology, directs the work of the laboratory represented in 
our illustration. It is a long apartment, perfectly lighted, 
into which stream the rays of the sun, that plays so 
important a part in all the phenomena of vegetable life ; 
on the right, ventilators carry off all the strong-smelling 
gases which the chemist is obliged to employ ; long tables, 
furnished with earthenware vessels, extend along the 
middle of the apartments as well as underneath the 
windows. Everything is scrupulously tidy. 
This laboratory of agricultural chemistry will no doubt 
yield to agricultural chemistry important results. The 
man of science will have here the means of preparing at 
pleasure true artificial soils ; he will see plants of various 
-kinds grow under his eyes; he will nourish them with 
organic and mineral substances whose composition is 
known to him. He will follow step by step the various 
phases of vegetable life ; he will study the yet mysterious 
laws of vegetable life. Indeed it is difficult to state all 
the powerful resources that are in the hands of the experi- 
menter, : 
AERIAL SPECTRES 
1 iy an article on the above subject in Za Nature, No. 4, 
M. G. Tissandier gives the following account of what 
he saw from a balloon on February 16, last. 
At mid-day we quitted the earth wrapped in a thick 
mantle of fog ; after traversing the mass of the clouds, 
we were suddenly dazzled by torrents of light which shot 
NATURE 
227 
have, in addition, “the light that never was on sea or 
land,’ 
When our balloon had passed about 50 metres beyond 
the plain of clouds, its shadow was projected with re- 
markable precision, and a magnificent circular rainbow 
appeared round the shadow of the car. Fig. 2 gives a 
very exact idea of the phenomenon. The shadow of the 
car formed the centre cf rainbow-colcured concentric 
circles, in which were distinctly seen the seven colours of 
the spectrum, violet, indigo, blue, green, yellow, orange, 
and red. The violet was inside, and the red on the out- 
side, these two colours being at the sane time those 
which wer>scen -v.th the greatest distinctn si. We were, 
Fic. 1.—Shadow of a balloon surrounded by three aureoles, 
from a tropical sun, a stream of fire, in the midst of an 
azuresky, Neither the mer de glace nor the snowy fields of 
the Alps, give an idea of the plateau of mist which 
stretched under the car like a glassy circle, in which 
valleys of silver appeared in the midst of flakes of gold. 
Neither the sea at sunset nor the ocean waves when 
lighted up by the orb of day at noon, approach in 
splendour this array of circular cumulus, but which 
G. 2,—Optical phenomenon observed from a ba loon. 
at the tine the observation was made, at a height of 
1,350 metres above the level of the sea. 
The balloon, the gas in which expanded under th2 heat 
of the sun, continued to rise rapidly in the air, its shadow 
visibly diminishing ; soon, at a height of 1,700 metres, the 
rainbow-circle enveloped it entire’y, and disappeared fiom 
around the car. AA little later, at about 1°35™, we 
approached the bed of clouds, and the shadow was girt 
this time by three silver-coloured aurioles, elliptical and 
concentric, as shown in Fig. 1, 
Nothing can give an idea of the purity of these 
shadows, which are cut out in an opaline mist, or of the 
delicacy of tone of the rainbow which surrounds them, 
The complete silence which reigns in the atrial rezions, 
where this play of light is seen, the absolute calm which 
