

Fuly 27, 1871) 
in no other way, and he held also that the polarisation experi- 
ments seemed to show the same thing. The Astronomer Royal 
was content to find the reflection, which so many now insist must 
be at the sun, taking place somewhere between the earth and 
moon. 
M. Madler’s verdict is in the same direction, and though he 
does not perhaps express so decided an opinion, he maintains 
that the atmosphere plays a principal part in the phenomenon ; 
and after detailing experiments to show this, he remarks of the 
solar and atmospheric portions, ‘‘ Both cover each other and 
unite in one phenomenon, so that the corona is a mixed phe- 
nomenon.” 
I shall shortly show you that the spectroscope, leaving the 
telescope out of consideration, has taught us that this is true ; 
tliough I shall not be able to show you that it is the whole truth ; 
we are not yet ina position to do that. Madler concludes his 
observations by remarking :—‘‘ We cannot share the doubts of 
those who are afraid to surround the sun with too many envelopes ; 
neither do we find anything unnatural in the statement that the 
sun has as many atmospheres as Saturn has rings ; but we gladly 
admit that we cannot yet say anything positive. We have here 
a large field of probabilities, and the decision may yet be 
distant.” 
We can speak with more certainty now ! 
IV.—SPECTROSCOPIC OBSERVATIONS 
a.— Spectrum of the Corena first observed by Tennant, Pogson, 
and Rayet 
We now come to the consideration of those observations in 
which we are aided bya most powerful and our most recent ally, 
the spectroscope, first used on the eclipsed sun, as you know, in 
the eclipse of 1868. You all know that in that year the question 
of the nature of red flames was for ever settled by M. Janssen, 
Major Tennant, Captain Herschel, and others, who observed 
that eclipse in the most admirable manner ; but we have nothing 
to do with the red flames now, we have to do with something 
outside them. 
Now, most of you are under the impression, and it was mine 
until the day before yesterday, that the only thing we learnt about 
the corona in the eclipse of 1868, was that its spectrum was a con- 
tinuous one ; and I need not tell anyone in this theatre that the as- 
sertion that it was continuous was one that was extremely embarrass- 
ing, and implied that we had something non-gaseous outside the red 
flames, which seemed very improbable to those who know anything 
about the subject. Butsome of you will no doubt remember that, 
besides Major Tennant, who made this observation, we had a 
French observer, M. Rayet, who gave us a diagram of the 
spectrum of one of the prominences, and Mr. Pogson, who has 
now been for some time in India, and is a well-known observer, 
who gaye us, nominaily as the spectrum of a prominence, a 
spectrum with some curious variaticns from M. Rayet’s diagram. 
T exhibit a copy of M. Rayet’s diagram of the spectrum of a 
prominence, as he called it. Atthe bottom is what he con- 
sidered as the spectrum of the lower portion of the prominence ; 
while in the higher portion, where we get fewer lines, as he con- 
sidered, is the spectrum of the higher portion of the prominence. 
The spectrum of the lower portion contains the lines B, D, E, 
and F, and some other lines, in all nine, while the spectrum of 
the upper part of the prominence, as he thought it, only con- 
tains three lines. It was at first difficult to account for these 
observations. In the first place, one could not understand 
the line B being given, because I soon found that the line 
B was not seen as a bright line in the chromosphere spectrum ; it 
was clearly the line C that was intended. Hence doubt was 
thrown on the other lines ; it seemed as if M. Rayet was wrong 
about his elongated lines D, I%, and F, and probably meant C 
near D and F, And so it was explained—I am ashamed to say 
by myself—that there was no particular meaning in these elon- 
gated lines, except that the spectrum of the prominence some 
distance away from the sun was simpler than it was nearer the 
sun, as happens in all prominences, as we may now determine 
any day we choose to look at the sun by means of the spectro- 
scope. j 
Now let us hear Mr. Pogson. He gave a diagram showing five 
lines in the spectrum of what he thought a prominence, and he 
writes :—‘‘ A faint light was seen (in the spectroscope), scarcely 
coloured, and certainly free from either dark or bright lines. 
While wondering at the dreary blank before me, and feeling 
intensely disappointed, some bright lines came gradually into 
view, reached a pretty considerable maximum brilliancy, and 

NATURE 
249 


again faded away. Five of these lines were visible, but two 
decidedly superior to the rest... . . The readings of the two 
brightest were secured. It struck me as strange that these 
brightest lines should appear at a part of the spectrum not cor- 
responding to any very conspicuous dark lines in the solar 
Spectrumsn ersten [These lines are a little less refrangible than 
E.] The third line seen in order of brilliancy must have been 
either coincident with, or very near the place of the sodium line 
D, but it was much fainter than the two measured, while the 
fourth and fifth lines were extremely faint.” {They were very 
faint and DOUBLED, and near F. I have seen F give way to a 
double line ia our hydrogen experiments, though I am not 
prepared to say this is an explanation of Mr. Pogson’s ob- 
servations. | 
The fact that we have here the first observations of the spect- 
rum of the sun’s corona is one beyond all doubt ; and why M. 
Rayet and Mr. Pogson thought they were observing prominences 
when they were observing above them, is explained by a remark 
made by Captain Tupman, of the Royal Marine Artillery, who 
acted as jackal to Prof. Harkness, and picked out the brighter 
spots of the corona for his observation. Prof. Harkness observ- 
ing the prominence bright lines, said to Captain Tupman, ‘‘ You 
have turned the telescope on to a prominence; I want the 
corona.” ‘*No,” said Captain Tupman, ‘‘I am giving you 
the corona as well as I can.” It was certainly the corona in 
both cases. Here you see, dimly and darkly, the first outcome 
of the spectroscope on the nature of the corona; a record as 
fairly written as anything at the sun can write it; and I am 
more anxious to lay stress on these observations, since they have 
lain fallow for two years, and show the importance of observa- 
tions, not only in extending our knowledge, but in explaining 
prior observations ; and it is an additional reason for never re- 
jecting an observation. What was, however, dim and dark in 
1868, shone out brightly in 1869, thanks to the skill of the 
American observers of the eclipse of that year. 
6.—Laboratory Experiments bearing on these Observations 
But before I proceed to refer to the admirable observations 
made in America during this eclipse, I wish to introduce you to 
some work which was commenced in 1868, and has been done 
quite independently of eclipses. In a lecture which I delivered 
here about two years ago, I described to you some of the facts 
observed by the spectroscope in the bright-line region which had 
been spectroscopically determined to exist all round the sun, and 
which, as in it all the various coloured effects are seen in total 
eclipses, I had named the Chromosphere. It was clear that by 
the new method of observing this without any eclipse, by partially 
killing, so to speak, the atmospheric light, we got a percentage 
only of the phenomenon, as the atmospheric light could only be 
killed by an amount of dispersion which enfeebled and shortened 
the chromospheric lines ; so that although we could say that an 
envelope of some 5,000 or 6,000 miles in height existed round the 
sun, we could not fix this asa maximum limit. Further, when 
we examined the spectrum of this envelope we got long lines and 
short lines; and I told how the short lines indicated a low 
stratum, and how a long line indicated a higher one. To explain 
this, I will show you an observation made long before the new 
method was thought of. Even before that time we had abun- 
dant evidence of such strata, if we could not determine their 
nature: we had distinct evidence either of one thing shinning 
out, and then another, or that various substances were situated 
at different levels, under different conditions; on the first hypo- 
thesis, at the extreme outside of the chromosphere the last thing 
would thin out, and then there would be an end of all things as 
respects the sun. 
I will show you a drawing made by Prof. Schmidt of the 
eclipse of 1851. I do not wish to call your attention to the 
strange shape of the large prominence, but to the fact, that as 
the moon passed over this region we get a thin red band, first 
along the edge of the dark moon, and after the moon had passed 
over still further, we see this red layer, sespended as it were in the 
chromosphere, with a white layer below it. This is the explana- 
tion of the long and short lines visible in the spectrum of the 
chromosphere ; in the red layer we have hydrogen almost alone ; 
below, its red light was conquered by other light with bright 
lines in all parts of the spectrum, and we get white light. 
Lord Lindsay tells me he has a distinct indication, written Ly 
the sun himself, that in one particular part of the chromosphere, as 
recorded photographically in Spain, there were three such layers. 
And over and over again we find recorded white light close to 
the sun, then red alone, or red mixed with ye!low, then violet, 
