May 13, 1886] 
INA PORE 
43 
being observed by Prof. Newcomb and myself—we were practi- 
cally close together at a height of 7000 feet—other observers 
were viewing the eclipse from Pike’s Peak, some few hundred 
miles away, at a height of 13,000 feet. You can imagine the 
purity of the air at that height ; there was not too much of it— 
so little in fact that some observers had to go down. ‘These saw 
the corona very well indeed ; and one or two observers, without 
taking the precaution of putting up a screen, saw an extension 
almost comparable with that recorded by Prof. Newcomb. 
That, then, we must take to be the undoubted result arrived 
at during the eclipse of 1878, which happened at the last sun- 
spot minimum. We have a tremendous equatorial extension ; 
that is the great feature, and it is proved by photographs. 
The drawing made in 1867 gives us the same result. We 
again get the equatorial extension east and west, and the wonder- 
ful outcurving right and left from the sun’s poles. 
Hence, then, we must associate a corona of that kind, 7.e. 
having a considerable equatorial extension, with that quiet con- 
dition of things at the sun, during which metallic prominences, 
ordinary prominences, faculz, and spots show a minimum of 
activity. 
You will remember that we saw from the sunspot curve that 
from minimum to maximum it mounts rapidly, reminding one of 
a steep cliff. We have in fact only three years from minimum 
to maximum, while we have eight years from maximum to 
minimum. 
The Approach to Maximum 
We have then next to consider the solar condition between 
minimum and maximum. We must suppose ourselves to be 
half-way up the steep part of the curve that connects the maxi- 
mum with the minimum. In this case we find a greater activity 
in all directions. The hydrogen—or the quiet—prominences are 
more numerous. ‘The facule are brighter. If we now examine 
the chromosphere we find hydrogen and D? are not the only con- 
stituents—we get those other short lines added of which Prof. 
Tacchini has given us such a valuable list, among them chiefly 
being those three lines of magnesium which are designated 
6, 6°, 64. That is the chemical difference between the chromo- 
sphere of the sun at this time, and the first period at which we 
considered it. The spots also are more numerous, and what 
spots there are we have in a lower latitude ; instead of making 
their appearance in latitude 35°, they will be nearer latitude 25° 
—they will have come down ro” from the solar poles towaids 
the equator. These more numerous spots will also be constantly 
accompanied by metallic prominences, and the number of lines 
visible as bright lines in these prominences we shall find in- 
creasing as the observations are made month after month. 
Ifow about the outer atmosphere of the sun? Well, remark- 
able changes begin to take place in it too. In considering the 
minimum corona I said nothing about its spectrum, for the reason 
that I wished that wonderful bilateral and symmetrical and simple 
form to rivet the attention. But now it is right that I should say 
that one of the chief changes between this coronaas the maximum 
is approached and the minimum one is not only the change of. 
form to which I shall have to draw attention, but a change in 
the spectrum. At the minimum sunspot period the corona gives 
exactly, or very nearly exactly, the same spectrum as the lime- 
light or a jet of gas—we get very nearly a continuous spectrum. 
The chief difference between the spectrum of the corona, then, 
and the spectrum of the gas jet, is that in this continuous corona 
spectrum certain dark lines will be seen, but no very obvious bright 
lines are there. We therefore have to come to the conclusion 
that at the minimum the corona is not chiefly gaseous in its spec- 
trum, but that it consists of solid particles to a very large extent ; 
and that these solid particles are not only competent to reflect 
light, but that they actually do reflect light coming from the 
lower portions of the sun; and in that way we account for the 
presence of the Fraunhofer lines. 
But when we come to the second period we are now discuss- 
ing, these change to a very large extent ; the spectrum is no 
longer continuous ; bright lines begin to make their appear- 
ance, and with this coming-in of bright lines comes in a greater 
brilliancy. 
And then as to the form. The diagram is copied from a 
drawing taken in the year 1858, at exactly the right period to 
illustrate any change which may have taken p'ace on the ap- 
proach to maximum. Unfortunately it is not a photograph. 
Those who lectur2 in this theatre twenty or a hundred years after 
me wil! be under many better conditions than we are, because | 
they will have a more complete series of photographs to refer 
to ; but in the absence of photographs we must do the best we 
can. Strange though the drawing is, it brings together so many 
features seen in other eclipses, that there is very little doubt 
that it is near the truth. However that may be, it must be 
acknowledged that between the last drawing you saw and this 
Fic. 20.—Corona of 1878. 
there is a most enormous difference. The remarkable point 
about it is that we have no special feature in the equatorial 
zone : we get a streamer here with very strange outlines, and 
we get another there, but the point of this drawing is that we 
get in middle latitudes, north and south, four wonderful Iuminous 
cones, and the amount of light and structure in the corona has 
increased to such an extent, that that exquisite, that beautiful 
tracery and double curves—curves east and curves west—we saw 
at both poles at the minimum, are now hidden in a strong 
radiance. So much then for the second act, so to speak, inthis 
solar drama. 
The Maximum 
We next deil with the maximum period when all the solar 
forces are working full time, and when we get both in prominences 
and in spots, and indeed in every outcome of action that we can 
refer to, indications of the most gigantic energies at work, and 
the most wonderful changes produced ; energies and changes dis- 
played from one pole of the sun to the other. When we come 
to this period of enormous action, we shall find that, although it 
becomes more general in one sense, it is really more limited in 
another. 
The ordinary prominences, instead of clinging to the equator 
as they have done previously, are now found to be most frequent 
at the solar poles ; the faculee are brighter and more spread over 
the solar surface than they have ever been before. The chromo- 
sphere is richer in lines. 
The spots occupy broad zones, the mean latitude being in 
about 18° N. and S. No spots near the poles, no spots 
near the equator, but spots indicating enormous activity and of 
enormous area, surrounded by gigantic faculee, will be seen 
following each other in these zones. We shall find every one 
of these indicators of solar activity accompanied by enormous 
prominences. It is at this time we get the greatest velocities 
of upthrow in the prominences, and the grea%est indications of 
tremendous downward velocity in the vapours which form the 
spots. Itis at this time we get the spots riddled by bridges of 
intense brilliancy, full of veiled tints, red, yellow, blue, and 
violet, and all those other more delicate and beautiful phe- 
nomena described by M. Trouvelot and others, to which I 
have drawn attention. 
How about the outer atmosphere of the sun? What has 
happened to that? Here, fortunateiy, we have the photographic 
records of two years—of two maximum years—to study. In these 
records there is no doubt that we have a thing which is abso- 
lutely and truly solar, forthe reason that the photograph has un- 
doubtedly, I think, sifted out what may be considered as due to 
non-solar causes. I say this distinctly, because I was fortunate 
enough to see both of these eclipses, one in India, and one in 
Egypt, and certainly there were things which I saw with the 
