ON THE ECLIPSE EXPEDITION, 1871* 
I UNDERSTAND my duty to-night to be to give an account 
of the observations made, not by all who observed the 
eclipse of last December, but by the members of the party which 
went out under the auspices of the British Association ; and it is 
extremely fortunate that nothing more is required of me—first, 
because most valuable work was done by the other parties, which 
of itself would require more time to state than I have at my dis- 
posal ; and secondly, because the amount of material obtained 
by the members who were sent out from England, and by the 
friends who met them at every point, is so great, that it would 
be impossible in one discourse to give anything like an exhaustive 
account of it. Here are some of the records in this portfolio. 
You will see at once that even for one party I can only make a 
selection, and I am perfectly aware of the extreme responsibility 
which attaches to anyone who may venture to make a selection 
out of such an enormous mass of material as we have collected. 
Before I proceed to discuss the work done by the different 
parties, it will be desirable to give an idea of the arrangements, 
and for this purpose I have prepared several maps which will 
enable you to see what the British Association parties did. 
. In the first instance I may remark that the weather conditions 
4 were somewhat problematical. Another point of great impor- 
tance was that much of the ground was fortunately occupied, and 
it was essential, when placing the parties, to bear these two con- 
siderations in mind—the possibility of bad weather, and then the 
. importance of so arranging matters that if some of the observers 
were clouded out, belonging to our parties, then the story might 
be continued by other observers. 
Here we have a map of India, which gives you a general idea 
of the path of the shadow during the eclipse. The shadow, you 
see, strikes India on the western coast, and it runs down in a 
south-westerly direction, and cuts the northern portion of Ceylon. 
When we arrived in India we found that the Indian observers, 
consisting of those well-known men Tennant, Herschel, Hen- 
nessy, Pogson, and others, had determined, from their know- 
ledge of the climatic conditions of India at that time of the year, 
to occupy the central part of the line, and also a station at a low 
level ; the eminent French physicist M. Janssen taking up his 
___ position at the top of the Nielgherries. We were to station our- 
___ selves either east or west, or both, of these parties. Whether 
east or west would depend upon the monsoon, and the great 
question that was being discussed on our arrival was, Was the 
_ monsoon favourable? 
I have not time to go into the many interesting points touch- 
ing the answer to this question ; but I may say shortly that what 
we heard was, that if the weather was likely to be bad on the 
east side of the hill range, generically called the Ghauts, there 
was a good chance for anyone occupying a position west of those 
hills. What happened was that we did occupy the positions 
marked by blue wafers on the map, namely, Bekul on the west 
» coast, Manantoddy on the western slope of the Ghauts, Poodo- 
cottah in the eastern plain, and in the island of Ceylon, first, 
Jaffna, and secondly, Trincomalee. 
Such were our arrangements. The parties were stationed 
along the line of totality. Very different were the arrangements 
of the Sicilian party of the former year. In Sicily we were com- 
. pelled to throw ourselves across the line of totality in the direc- 
tion which I have indicated on this map of Sicily. 
Now what was the work wehad todo? If you will allow me 
to refer to two or three results of the former Eclipse Expedition, 
I will endeavour to put them before you without taking up too 
much of your time. 
One of the most important among the results obtained in the 
eclipse of 1870 was this: far above the hydrogen which we can 
see every day without an eclipse—far above the prominences, the 
spectrum of hydrogen had without doubt been observed by two 
or three of the American observers, who were more fortunate 
than we were. Among them Prof. Young stated that the spec- 
trum of hydrogen was observed to a distance of 8 minutes from 
the sun ; he then adds, ‘‘ far above any possible hydrogen atmo- 
sphere.” This is point number one. 
Another of the points was this : the unknown substance which 
gives usa line coincident, according to Young, with a line num- 
bered 1474 by Kirchhoff, had been observed by the American 
* A Lecture delivered at the Royal Institution of Great Britain, Monday, 
March 22, 1872, by J. Norman Lockyer, F.R.S. (The chief results ob- 
tained by the expedition have been taken from the ad interim Report pre- 
sented to the British Association Meeting at Brighton. The lecture itself 
dealt mainly with the methods and instruments employed.—J. N. L.) 
“ 
NATURE 
57 
observers to a height of 20 minutes above the limb of the dark 
moon, 
Now, it was a very obvious consideration that if we got a 
spectrum of hydrogen 8 minutes from the dark moon, when we 
thought we knew that the hydrogen at the sun did not really ex- 
tend more than 10 seconds beyond the dark moon, there was 
something at work which had the effect of making it appear very 
much more extensive than it really was ; and it was fair to assume 
that if this happened in the case of the hydrogen, it might 
also happen in the case of the unknown stuff which gives us the 
line 1474. 
In support of this view we had one of the few observations 
which were made in Sicily, in the shape of a drawing of the 
corona, as seen by Prof. Watson, who observed at Carlentini. 
He saw the corona magnificently ; and being furnished with a 
powerful telescope, he made a most elaborate drawing of it, a 
rough copy of which I will throw on the screen. You will see 
at once that we had in this drawing something which seemed to 
militate against the idea that the 1474 stuff at the sun did exist 
to a height of 20 minutes. According to Prof. Watson the 
boundary of the real corona was clearly defined, its height being 
far under that stated. 
Next, we had another observation of most important bearing 
on our knowledge of the base of the corona. TI refer to the an- 
nouncement of the observation by Prof. Young of a stratum in 
which all the Fraunhofer lines were reversed. It was asserted that 
there was undoubtedly a region some 2 seconds high all round 
the sun, which reversed for us all the lines which are visible in 
the solar spectrum. We had, in fact, in a region close to the 
photosphere the atmosphere of the sun demanded by Kirchhoff 
at some distance above the photosphere. 
Last, not least, we had the photographic evidence. There 
was in Sicily a photographic station in Syracuse, and the Ame- 
ricans had another in Spain. I now show on the screen a 
drawing—it is not the photograph itself—but a drawing of a 
photograph made by the party in Sicily ; what we have on this 
photograph is a bright region round the dark moon, which is, 
undoubtedly, solar, but stretching out right away from this, 
here and there are large masses of faint light, with dark spaces 
between them, which have been called rifts. Now the question 
is, Is this outer portion solar ? ’ 
Having thus brought rapidly before you some of the questions 
which we had principally to bear in mind, and, if possible, 
settle (though that is too much to hope for in any one Eclipse 
Expedition) in the work we had to do in India, I will next 
bring to your notice some new methods of inquiry which had 
been proposed, with the object of extending former observa- 
tions. 
I may here remark that the Royal Astronomical Society, in 
the first instance, invited me to take charge of an expedition to 
India merely to conduct spectroscopic observations ; but 
although this request did me infinite honour, I declined it, be- 
cause the spectroscope alone, as it had been used before, was, 
in my opinion, not competent to deal with all the questions then 
under discussion. I have told you that some of the most emi- 
nent American observers had come to the conclusion that the 
spectrum of hydrogen observed in the last eclipse round the 
sun, to a height of 8 minutes, was a spectrum of hydrogen 
‘*far above any possible hydrogen” at the sun. Hence it was 
in some way reflected. Now with our ordinary spectroscopic 
methods it was extremely difficult, and one might say impos- 
sible, to determine whether the light which the spectroscope 
analysed was really reflected or not ; and that was the whole 
question. 
It became necessary, therefore, in order to give any approach 
to hopefulness, to proceed in a somewhat different way in the ~ 
1871 expedition ; and, in order to guard against failure, to sup- 
plement such new observations by photographs ; and fortunately 
we were not long in coming to a conclusion that this might be 
done with some considerable chance of success. 
T have here a train of prisms. I will for one moment take 
one prism out of the train, and we will consider what will hap- 
pen if we illuminate the slit of the lantern with a monochroma- 
tic light, and observe it through the prism. If we render sodium 
vapour incandescent, we know we get a bright yellow image of 
the slit, due to the vapour of the metallic sodium only giving us 
yellow light. But why is it that we get aline? Because we 
always employ a line for the slit, But suppose we vary the in- 
quiry? If, instead of a straight line we have a crooked line for 
the slit, then we ought to see a crooked line through the prism. 
eos 
