SOLAR RESEARCHES BY JANSSEN—PLUVINEL. 245 
aeronautical meetings, and in giving bountiful hospitality, at Meu- 
don, to the International Congress of Aerostation. 
In the year after the eclipse of 1870 there came another, visible this 
time in India and Java. Janssen was careful not to lose this new 
opportunity for the examination of the solar envelopes. <A careful 
study of the meteorological aspects of the various places where the 
eclipse might be visible made him adopt a station in India, in the 
Neelgheries; the outcome showed the justice of his choice, for it 
would have been scarcely possible to observe an eclipse under more 
favorable conditions. This time Janssen confined his attention prin- 
cipally to the corona. He noted in the spectrum of this, not only 
the green ray, whose presence was already known, but also dark 
lines, indicating that a part of the light of the corona is reflected 
sunlight, and tending to prove that the coronal envelope is not 
exclusively gaseous but composed partly of liquid or solid particles. 
In 1875 we again find Janssen observing an eclipse, this time near 
the island of Malacca, on the return voyage from a trip to Japan. 
Then, in 1883, with no fear for the fatigue of a difficult voyage, 
he went to the island of Carolina, in the middle of the Pacific Ocean, 
in order to observe a total solar eclipse remarkable for the duration 
of totality. Thanks to the silver-bromide gelatine dry plates, which 
had then just been invented, he was able to photograph the phe- 
nomena of this eclipse under very varied conditions, and brought 
back data of the greatest interest on the extent of the solar corona. 
Before terminating this work Janssen wished to observe for a 
last time these beautiful phenomena, which for him had always had 
such a fascination. So, in 1905, despite his advanced age, he went 
to Spain to have the pleasure of seeing an eclipse, more as a curious 
human being than as an astronomer. 
We have now seen what Janssen accomplished in the investiga- 
tion of the gaseous surroundings of the sun by the application of 
the spectroscope to the study of solar eclipses. We will now pass 
in review his work upon the absorption of our own atmosphere 
for the radiation from the sun. 
The first of these spectroscopic studies relates to the black bands 
which appear in the sun’s spectrum as the sun nears the horizon. 
These had already been noted by Sir David Brewster, but the latter 
recognized neither the real structure of these bands nor the cause 
of their appearance. By observations made in Rome from 1862 to, 
1863 Janssen found that these bands were resolvable into lines, and 
proved that their origin must be attributed to the selective absorp- 
tion produced upon the solar rays by the gases of our own atmos- 
phere. Later it was found that the oxygen in the air produced the 
bands A, a, and B, which appear in the solar spectrum. But the 
oxygen of our atmosphere might not be the only oxygen giving 
