of voices,--it was all over, and what had been missed then could not
be recovered. The sense of self-reproach for wasted opportunity is
a common enough feeling at this time, though one may have done his
best, so little it seems to each he has accomplished; but when all the
results had been brought together, we found that the spectroscopes,
cameras, and polariscopes had each done their work, and the journey had
not been taken in vain. In one point only we all differed, and this
was about the direct ocular evidence, for each seemed to have seen a
different corona, and the drawings of it were singularly unlike. Here
are two (Figs. 33 and 34) taken at this eclipse at the same time,
and from neighboring stations, by two most experienced astronomers,
Tacchini and Watson. No one could guess that they represented the same
object, and a similar discrepancy was common.
[Illustration: FIG. 37.--ENLARGEMENT OF PART OF FIG. 38.]
Considering that these were trained experts, whose special task it
was, in this case, to draw the corona, which therefore claimed their
undivided attention, I hardly know a more striking instance of the
fallibility of human testimony. The evidence of several observers,
however, pointed to the fact that the light really was more nearly
confined to the part next the sun than the year before, so that the
corona had probably changed during that interval, and grown smaller,
which was remarkable enough. The evidence of the polariscope, on the
whole, showed it to be partly due to reflected sunlight, while the
spectroscope in the hands of Professor Young confirmed the last year’s
observation, that it was also, and largely, self-luminous. Finally,
the photographs, taken at very distant stations, showed the same dark
rifts in the same place, and thus brought confirmatory evidence that
it was not a local phenomenon in our own atmosphere. A photograph of
it, taken by Mr. Brothers in Sicily, is the subject of the annexed
illustration (Fig. 35), in which the very bright lights which, owing to
“photographic irradiation,” seem to indent the moon, are chiefly due to
the colored flames I have spoken of, which will be described later.
It may be observed that the photographs taken in the next year (1871)
were still more successful, and began to show still more of the
structure, whose curious forms, resembling large petals, had already
been figured by Liais. His drawing (Fig. 36), made in 1857, was
supposed to be rather a fanciful sketch than a trustworthy one; but, as
it will be seen, the photograph goes far to justify it.
Figures 37 and 38 are copies published by Mr. Ranyard of the excellent
photographs obtained in 1871, which are perhaps as good as anything
done since, though even these do not show the outer corona. The first
is an enlargement of a small portion of the detail in the second. It is
scarcely possible for wood-engraving to reproduce the delicate texture
of the original.
[Illustration: FIG. 38.--FAC-SIMILE OF PHOTOGRAPH OF CORONA OF 1871.
(ROYAL ASTRONOMICAL SOCIETY’S MEMOIRS.)]
The years brought round the eclipse of 1878, which was again in United
States territory, the central track (as Fig. 30 has already shown)
running directly over one of the loftiest mountains of the country,
Pike’s Peak, in Colorado. Pike’s Peak, though over fourteen thousand
feet high, is often ascended by pleasure tourists; but it is one thing
to stay there for an hour or two, and another to take up one’s abode
there and get acclimated,--for to do the latter we must first pass
through the horrors (not too strong a word) of mountain-sickness.
This reaches its height usually on the second or third day, and is
something like violent sea-sickness, complicated with the sensations
a mouse may be supposed to have under the bell of an air-pump. After
a week the strong begin to get over it, but none but the very robust
should take its chances, as we did, without preparation; for on the
night before the eclipse the life of one of our little party was
pronounced in danger, and he was carried down in a litter to a cabin at
an altitude of about ten thousand feet, where he recovered so speedily
as to be able to do good service on the following day. The summit
of the “Peak” is covered with great angular bowlders of splintered
granite, among which we laid logs brought up for firewood, and on
these, sacks of damp hay, then stretching a little tent over all and
tying it down with wire to the rocks, we were fain to turn in under
damp blankets, and to lie awake with incessant headache, drawing long,
struggling breaths in the vain attempt to get air, and wondering how
long the tent would last, as the canvas flapped and roared with a noise
like that of a loose sail in a gale at sea, with occasional intervals
of a dead silence, usually followed by a gust that shoved against the
tent with the push of a solid body, and if a sleepers shoulders touched
the canvas, shouldered him over in his bed. The stout canvas held, but
the snow entered with the wind and lay in a deep drift on the pillow,
when I woke after a brief sleep toward morning, and, looking out on the
gray dawn, found that the snow had turned to hail, which was rattling
sharply on the rocks with an accompaniment of thunder, which seemed to
roll from all parts of the horizon. The snow lay thick, and the sheets
of hail were like a wall, shutting out the sight of everything a few
rods off, and this was in July! I thought of my December station in
sunny Andalusia.
[Illustration: FIG. 39.--“SPECTRES.”]
Hail, rain, sleet, snow, fog, and every form of bad weather continued
for a week on the summit, while it was almost always clear below.
It was often a remarkable sight to go to the edge and look down. The
expanse of “the plains,” which stretched eastward to a horizon line
over a hundred miles distant, would be in bright sunshine beneath,
while the hail was all around and above us; and the light coming _up_
instead of down gave singular effects when the clouds parted below, the
plains seeming at such times to be opalescent with luminous yellow and
green, as though the lower world were translucent, and the sun were
beneath it and shining up through. Fig. 39 is a picture of three of us
on the mountain-top, who saw a rarer spectacle; for directly opposite
the setting sun, and on the mist over the gulf beyond us, was a bright
ring, in whose centre were three phantom images of our three selves,
which moved as we moved, and then faded as the sun sank. It was “the
spectre of the Brocken.” These ghostly presentments were tolerably
defined, as in the sketch, but did not seem to be gigantic, as some
have described them. We rather thought them close at hand; but before
we could determine, the vision faded.
The clouds, to our good fortune, rolled away on the 29th; and a
number of pleasure-seekers, who came up to view the eclipse and the
unwonted bright sunshine, made a scene which it was hard to identify
with the usual one. This time my business was to draw the corona; and
the extreme altitude and the clearness of the air, with perhaps some
greater extension than usual in the object itself, enabled it to be
followed to an unprecedented distance. During totality the sun was
surrounded by a narrow ring--hardly more than a line--of vivid light,
presenting no structure to the naked eye (but a remarkable one in
the telescope); and this faded with great suddenness into a circular
nebulous luminosity between two and three diameters of the sun wide,
but without such marked plumes, or filaments, as I had seen in 1869.
The most extraordinary thing, however, was a beam of light, inclined
at an angle of about forty-five degrees, about as wide as the sun,
and extending to the distance of nearly six of its diameters on one
side and over twelve on the other; on one side alone, that is, to the
amazing distance of over ten million miles from its body. Substantially
the same observation was made, as it appeared later, by Professor
Newcomb, at a lower level. The direction, when more carefully measured,
it was interesting to note, coincided closely with that of the Zodiacal
light, and a faint central rib added to its resemblance to that body.
It is noteworthy, in illustration of what has already been said as
to the conflict of ocular testimony, that though I, with the great
majority of observers below, saw only this beam, two witnesses whose
evidence is unimpeachable, Professors Young and Abbe, saw a pale beam
at right angles to it; and that one observer did not see the beam in
question at all. Fig. 40 is a sketch made from my own, but necessarily
on a scale which can show only its general features.
With the telescope, the whole of the bright inner light close to the
sun was found to be made up of filaments, more definite even than those
described in a previous chapter as seen in sun-spots, and bristling in
all directions from the edge; not concealing each other, as we might
expect such things to do, upon a sphere, but fringing the sun’s edge in
definite outline, as though it were really but a disk.
[Illustration: FIG. 40.--OUTER CORONA OF 1878. (U. S. NAVAL
OBSERVATORY.)]
Those who were at leisure to watch the coming shadow of the moon
described its curved outline as distinctly visible on the plains. “A
rounded ball of darkness with an orange-yellow border,” one called
it. Those, again, who looked down on the bright clouds below say the
shadow was preceded by a yellow fringe, casting a bright light over
the clouds and passing into orange, pink, rose-red, and dark-red, in
about twenty seconds. This beautiful effect was noticed by nearly all
the amateur observers present, who had their attention at liberty, and
was generally unseen by the professional ones, who were shut up in dark
tents with photometers, or engaged otherwise than in admiring the glory
of the spectacle as a spectacle merely. This strange light, forming a
band of color about the shadow as seen from above, must have really
covered ten miles or more in width, and have occupied a considerable
fraction of a minute in passing over the heads of those below, to whom
it probably constituted that lurid light on their landscape I have
spoken of as so peculiar and “unnatural.” It seems to be due to the
colored flames round the sun, which shine out when its brighter light
is extinguished. I should add that on the summit of Pike’s Peak the
corona did not entirely disappear at the instant the sun broke forth
again, but that its outlying portions first went and then its brighter
and inner ones, till our eager gaze, trying to follow it as long as
possible, only after the lapse of some minutes saw the last of the
wonderful thing disappear and “fade into the light of common day.”
[Illustration: FIG. 41.--SPECTROMETER SLIT AND SOLAR IMAGE. (FROM “THE
SUN,” BY YOUNG.)]
There have been other eclipses since; but, in spite of all, our
knowledge of the corona remains very incomplete, and if the most
learned in such matters were asked what it was, he could probably
answer truthfully, “I don’t know.”
[Illustration: FIG. 42.--SLIT AND PROMINENCES.
(“THE SUN,” BY YOUNG.)]
This will not be wondered at when it is considered that as total
eclipses come, about every other year, and continue, one with another,
hardly three minutes, an astronomer who should devote thirty years
exclusively to the subject, never missing an eclipse in whatever
quarter of the globe it occurred, would in that time have secured,
in all, something like three-quarters of an hour for observation.
Accordingly, what we know best about the corona is how it looks, what
it _is_ being still largely conjecture; and it is for this reason that
I have thought the space devoted to it would be best used by giving the
unscientific reader some idea of the visible phenomena as they present
themselves to an eyewitness. Treatises like Lockyer’s “Solar Physics,”
Proctor’s “The Sun,” Secchi’s “Le Soleil,” and Young’s “The Sun” (the
latter is most recent), will give the reader who desires to learn more
of the little that is known, the fuller information which this is not
the place for; but it may be said very briefly that it is certain that
the corona is at times of enormous extent (the whole length of the
longer beam seen on Pike’s Peak must have been over fourteen million
miles), that it almost certainly changes in its shape and dimensions
from year to year (possibly much oftener, but this we cannot yet
know), and that it shines partly by its own and partly by reflected
light. When we come to ask whether it is a gas or not, the evidence
is conflicting. The appearance of the green coronal line, and other
testimony we have not alluded to, would make it seem almost certain
that there must be a gas here of extreme tenuity, reaching the height
of some hundred thousand miles, at the least; while yet the fact that
such light bodies as comets have been known to pass through it, close
to the sun, without suffering any visible retardation, such as would
come even from a gas far lighter than hydrogen, appears to throw doubt
on evidence otherwise strong. It is possible to conceive of the corona,
and especially of the outer portion, as very largely made up of minute
particles such as form the scattered dust of meteoric trains, and this
seems to be the most probable constitution of its outlying parts. It
is even possible to conceive that it is in some degree a subjective
phenomenon, caused, as Professor Hastings has suggested, by diffraction
upon the edge of the moon,--the moon, that is, not merely serving as a
screen to the sun to reveal the corona, but partly _making_ the corona
by diffracting the light, somewhat as we see that the edge of any very
distant object screening the sun is gilded by its beams. This effect
may be seen when the sun rises or sets unusually clear, for objects on
the horizon partly hiding it are then fringed for a moment with a line
of light,--an appearance which has not escaped Shakspeare, where he
says,--
“But when from under this terrestrial ball
He fires the tall tops of the eastern pines.”
Still, in admitting the possibility of some such contributory effect on
the part of the moon, we must not, of course, be understood as meaning
that the corona as a whole does not have a real existence, quite
independent of the changes which the presence of the moon may bring;
and in leaving the wonderful thing we must remember that it is, after
all, a reality, and not a phantasm.
[Illustration: FIG. 43.--TACCHINI’S CHROMOSPHERIC CLOUDS. (“MEMORIE
DEGLI SPETTROSCOPISTI ITALIANI.”)]
[Illustration: FIG. 44.--TACCHINI’S CHROMOSPHERIC CLOUDS. (“MEMORIE
DEGLI SPETTROSCOPISTI ITALIANI.”)]
I have already described how, at the eclipse of 1870, I (with others)
saw within the corona what seemed like rose and scarlet-colored
mountains rising from the sun’s edge, an appearance which had first
been particularly studied in the eclipse of 1868, two years before, and
which, it might be added, Messrs. Lockyer and Janssen had succeeded in
observing without an eclipse by the spectroscope. Besides the corona,
it may be said, then, that the sun is surrounded by a thin envelope,
rising here and there into prominences of a rose and scarlet color,
invisible in the telescope, except at a total eclipse, but always
visible through the spectroscope. It is within and quite distinct
from the corona, and is usually called the “chromosphere,” being a
sort of sphere of colored fire surrounding the sun, but which we can
usually see only on the edge. “The appearance,” says Young, “is as if
countless jets of heated gas were issuing through vents and spiracles
over the whole surface, thus clothing it with flame, which heaves and
tosses like the blaze of a conflagration.” Out of this, then, somewhat
like greater waves or larger swellings of the colored fires, rise the
prominences, whose place, close to the sun’s edge, has been indicated
in many of the drawings and photographs just given of the corona, on
whose background they are seen during eclipses; but as they can be
studied at our leisure with the spectroscope, we have reserved a more
particular description of them till now. They are at all times directly
before us, as well as the corona; but while both are yet invisible from
the overpowering brightness of the sunlight reflected from the earth’s
atmosphere in front of them, these red flames are so far brighter than
the coronal background, that if we could only weaken this “glare” a
little, they at least might become visible, even if the corona were
not. The difficulty is evidently to find some contrivance which will
weaken the “glare” without enfeebling the prominences too; and this the
spectroscope does by diffusing the white sunlight, while it lets the
color pass nearly unimpaired. For the full understanding of its action
the reader must be referred to such works as those on the sun already
mentioned; but a general idea of it may be gathered, if we reflect
that white light is composed of every possible variety of colors, and
that the spectroscope, which consists essentially of a prism behind a
very narrow slit through which the light enters, lets any single color
pass freely, without weakening it or altering it in anything but its
direction, but gives a different direction to each, and hence sorts out
the tints, distributing them side by side, every one in its own place,
upon the long colored band called the spectrum. If this distribution
has spread the colors along a space a thousand times as wide as the
original beam, the average light must be just so much weaker than the
white light was, because this originally consisted of a thousand (let
us say a thousand, but it is really an infinite number) mingled tints
of blue, green, yellow, orange, and red, which have now been thus
distributed. If, however, we look through the prism at a rose-leaf, and
it has no blue, green, yellow, or orange in it, and nothing but pure
red, as each single color passes unchanged, this red will, according
to what has been said, be as bright after it has passed as before. All
depends, then, on the fact that these prominences do consist mainly
of light of one color, like the rose-leaf, so that this monochromatic
light will be seen through the spectroscope just as it is, while the
luminous veil of glaring white before it will seem to be brushed away.
If a large telescope be directed toward the sun, the glass at the
farther end will, if we remove the eye-piece, form a little picture
of the sun, as a picture is formed in a camera-obscura; and now, if
we also fasten the spectroscope to this eye-end, where the observer’s
head would be were he looking through, the edge of the solar image may
be made to fall just _off_ the slit, so that only the light from the
prominences (and the white glare about them) shall pass in. To see
this more clearly, let us turn our backs to the sun and the telescope,
and look at the place where the image falls by the spectroscope slit,
which in Fig. 41 is drawn of its full size. This is a brass plate,
having a minute rectangular window, the “slit,” in it. The width of
this slit is regulated by a screw, and any rays falling into the
narrow aperture pass through the prism within, and finally fall on the
observer’s eye, but not till they have been sorted by the prism in
the manner described. Formed on the brass plate, just as it would be
formed on a sheet of paper, or anything else held in the focus, we see
the bright solar image, a circle of light perhaps an inch and a half
in diameter,--a miniature of the sun with its spots. The whole of the
sun (the photosphere) then is hidden to an observer who is looking up
through the slit from the other side, for, as the sun’s edge does not
quite touch the slit, none of its rays can enter it; but if there be
also the image here of a prominence, projecting beyond the edge, and
really overhanging the slit (though to us invisible on account of the
glare about it), these rays will fall into the slit and pass down to
the prism, which will dispose of it in the way already stated.
[Illustration: FIG. 45.--VOGEL’S CHROMOSPHERIC FORMS. (“BEOBACHTUNGEN,”
DR. H. C. VOGEL.)]
And now let us get to the other side, and, looking up through the prism
with the aid of a magnifying-glass, see what it has done for us (Fig.
42). The large rectangular opening here is the same as the small one
which was visible from the outside, only that it is now magnified, and
what was before invisible is seen; the edge of the sun itself is just
hidden, but the scarlet flames of the chromosphere have become visible,
with a cloudy prominence rising above them. The “flames” are flame-like
only in form, for their light is probably due not to any combustion,
but to the glow of intensely heated matter; and as its light is not
quite pure red, we can, by going to another part of the spectrum, see
the same thing repeated in orange, the effect being as though we had a
number of long narrow windows, some glazed with red, some with orange,
and some with other colors, through which we could look out at the
same clouds. I have looked at these prominences often in this way; but
I prefer, in the reader’s interest, to borrow from the description by
Professor Young, who has made these most interesting and wonderful
forms a special study.
Let us premise that the depth of the crimson shell out of which they
rise is usually less than five thousand miles, and that though the
prominences vary greatly, the majority reach a height of nearly twenty
thousand miles, while in exceptional cases this is immensely exceeded.
Professor Young has seen one which grew to a height of three hundred
and fifty thousand miles in an hour and a half, and in half an hour
more had faded away.
These forms fall into two main classes,--that of the quiet and
cloud-like, and that of the eruptive,--the first being almost exactly
in form like the clouds of our own sky, sometimes appearing to lie on
the limb of the sun like a bank of clouds on the horizon, sometimes
floating entirely free; while sometimes “the whole under surface is
fringed with down-hanging filaments, which remind one of a summer
shower hanging from a heavy thunder-cloud.”
Here are some of the typical forms of the quieter ones:--
Fig. 43, by Tacchini, the Director of the Roman Observatory, represents
an ordinary prominence, or cloud-group in the chromosphere, whose
height is about twenty-five thousand miles. The little spires of flame
which rise, thick as grass-blades, everywhere from the surface, are
seen on its right and left.
[Illustration: FIG. 46.--TACCHINI’S CHROMOSPHERIC FORMS. (“MEMORIE
DEGLI SPETTROSCOPISTI ITALIANI.”)]
Fig. 44 (Tacchini) is one where the agitation is greater and the
“filamentary” type is more marked. Besides the curiously thread-like
forms (so suggestive of what we have already seen in the photosphere),
we have here what looks like an extended cloudy mass, drawn out by a
horizontally moving wind.
Fig. 45 (by Vogel, at Bothkamp) represents another of these numerous
types.
The extraordinary Fig. 46 is from another drawing, by Tacchini, of a
protuberance seen in 1871 (a time of great solar disturbance), and it
belongs to the more energetic of its class.
[Illustration: FIG. 47.--ERUPTIVE PROMINENCES. (“THE SUN,” BY YOUNG.)]
This fantastic cloud-shape, “if shape it might be called that shape had
none,” looking like some nightmare vision, was about fifty thousand
miles long and sixty thousand high above the surface. The reader will
notice also the fiery rain, like the drops from a falling rocket, and
may add to it all, in imagination, the actual color, which is of a deep
scarlet.
It may add to the-interest such things excite, to know that they
have some mysterious connection with a terrestrial phenomenon,--the
aurora,--for the northern lights have been again and again noticed to
dance in company with these solar displays.
The eruptive prominences are very different in appearance, as will be
seen by the next illustration, for which we are indebted to Professor
Young.
In Fig. 47 we have a group of most interesting views by him (drawn
here on the common scale of seventy-five thousand miles to an inch),
illustrating the more eruptive types, of which we will let him speak
directly. The first shows a case of the vertical filaments, like those
rocket-drops we saw just, now in Tacchini’s drawing, but here more
marked; while the second (on the left side) is a cyclone-form, where
the twisted stems suggest what we have seen before in the “bridges” of
sun-spots, and below this is another example of filamentary forms.