grounded ones derived from this fruitful series of investigation.
Professor Langley has effected a redistribution of energy in the
solar spectrum. The maximum of heat was placed by former inquirers in
the obscure tract of the infra-red; he has promoted it to a position
in the orange approximately coincident with the point of greatest
luminous intensity. The triple curve, denoting by its three distinct
summits the supposed places in the spectrum of the several maxima
of heat, light, and “actinism,” must now finally disappear from our
text-books, and with it the last vestige of belief in a corresponding
threefold distinction of qualities in the solar radiations. From one
end to the other of the whole gamut of them, there is but one kind of
difference—that of wave-length, or frequency in vibration; and there
is but one curve by which the rays of the spectrum can properly be
represented—that of energy, or the power of doing work on material
particles. What the effect of that work may be, depends upon the
special properties of such material particles, not upon any recondite
faculty in the radiations.
These brilliant results of a month’s bivouac encourage the most
sanguine anticipation as to the harvest of new truths to be gathered by
a steady and well-organized pursuance of the same plan of operations.
It must, however, be remembered that the scheme completed on Mount
Whitney had been carefully designed, and in its preliminary parts
executed at Alleghany. The interrogatory was already prepared; it
only remained to register replies, and deduce conclusions. Nature
seldom volunteers information: usually it has to be extracted from her
by skilful cross-examination. The main secret of finding her a good
witness consists in having a clear idea beforehand what it is one wants
to find out. No opportunities of seeing will avail those who know not
what to look for. Thus, not the crowd of casual observers, but the few
who consistently and systematically _think_, will profit by the
effort now being made to rid the astronomer of a small fraction of his
terrestrial impediments. It is, nevertheless, admitted on all hands
that no step can at present be taken at all comparable in its abundant
promise of increased astronomical knowledge to that of providing
suitably elevated sites for the exquisite instruments constructed by
modern opticians.
Europe has not remained behind America in this significant movement.
An observatory on Mount Etna, at once astronomical, meteorological,
and seismological, was nominally completed in the summer of 1882,
and will doubtless before long begin to give proof of efficiency in
its threefold capacity. The situation is magnificent. Etna has long
been famous for the amplitude of the horizon commanded from it and
the serenity of its encompassing skies favors celestial no less than
terrestrial vision. Professor Langley, who made a stay of twenty days
upon the mountain in 1879-80, with the object of reducing to strict
measurement the advantages promised by it, came to the conclusion that
the “seeing” there is better than that in England (judging from data
given by Mr. Webb) in the proportion of three to two—that is to say,
a telescope of two inches aperture on Etna would show as much as one
of three in England. Yet the circumstances attending his visit were
of the least favorable kind. He was unable to find a suitable shelter
higher up than Casa del Bosco, an isolated hut within the forest belt
(as its name imports), at considerably less than half the elevation of
the new observatory; the imperfect mounting of his telescope rendered
observation all but impossible within a range of 30 degrees from the
zenith, thus excluding the most serene portion of the sky; moreover,
his arrival was delayed until December 25th, when the weather was
thoroughly broken, high winds were incessantly troublesome, and only
five nights out of seventeen proved astronomically available. It is,
accordingly, reassuring to learn that while, with the naked eye, at
ordinary levels, he could see but six Pleiades, with glimpses of a
seventh and eighth, on Etna he steadily distinguished nine even before
the moon had set;[23] and that the telescopic definition though not
uniformly good, was on December 31st such as he had never before
seen on the sun, “least of all with a blue sky;”[24] the “rice-grain”
structure came out beautifully under a power of 212; and for the
spectroscopic examination of prominences, the fainter orange light of
their helium constituent served almost equally well with the strong
radiance of the crimson ray of hydrogen (C)—a test of transparency
which those accustomed to such studies will appreciate.
The Etnean observatory is the most elevated building in Europe. It
stands at a height above the sea of 9,655 ft., or 1,483 ft. above the
monastery of the Great St. Bernard. Its walls enclose the well-known
“Casa Inglese,” where travellers were accustomed to spend the night
before undertaking the final ascent of the cone, and occupy a site
believed secure from the incursions of lava. Astronomical work is
designed to be carried on there from June to September. For the Merz
equatorial, 35 centimetres (13·8 inches) in aperture, which is _facile
primus_ of its instrumental equipment, a duplicate mounting has been
provided at Catania, whither it will be removed during the winter
months. The primary aim of the establishment is the study of the
sun. Its great desirability for this purpose formed the theme of the
representations from Signor Tacchini (then director of the observatory
of Palermo, now of that of the Collegio Romano), which determined
the Italian government upon trying the experiment. But we hear with
pleasure that stellar spectroscopy will also come in for a large share
of attention. The privilege of observation from the summit of Etna will
not be enjoyed exclusively by the local staff. The Municipality of
Catania who have borne their share in the expense of the undertaking,
generously propose to give it somewhat of an international character,
by providing accommodation for any foreign astronomers who may
desire to enjoy a respite from the hampering conditions of low-level
star-gazing. We cannot doubt that such exceptional facilities will be
turned to the best account.
Eight years have now passed since General de Nansonty, aided by the
engineer Vaussenat, established himself for the winter on the top of
the Pic du Midi. Zeal for the promotion of weather-knowledge was the
impelling motive of this adventure, which included, amongst other rude
incidents, a snow-siege of little less than six months. It resulted in
crowning one of the highest crests of the Pyrenees with a permanent
meteorological observatory opened for work in 1881. It is now designed
to render the station available for astronomical purposes as well.
The important tasks in progress at the Paris observatory have of
late been singularly impeded by bad weather. During the latter half
of 1882 scarcely four or five good nights per month were secured,
and in December these were reduced to two.[25] Moreover, M. Thollon,
who, according to his custom, arrived from Nice in June for the
summer’s work, returned thither in September without having found the
opportunity of making _one single_ spectroscopic observation. Yet
within easy and immediate reach was a post, already in scientific
occupation, where as General de Nansonty reported, ordinary print was
legible by the radiance of the milky way and zodiacal light alone,
and fifteen or sixteen Pleiades could be counted with the naked
eye. At length Admiral Mouchez, the energetic director of the Paris
observatory, convinced of the urgent need of an adjunct establishment
under less sulky skies, issued to MM. Thollon and Trépied a commission
of inquiry into telescopic possibilities on the Pic du Midi. Their stay
lasted from August 17th, to September 22d, 1883, and their experiences
were summarised in a note (preliminary to a detailed report) published
in the “Comptes Rendus” for October 16th, glowing with a certain
technical enthusiasm difficult to be conveyed to those who have never
strained their eyes to catch the vanishing gleam of a “chromospheric
line” through a “milky” sky, and dim and tremulous air. The definition,
they declared, was simply marvellous. Not even in Upper Egypt had they
seen anything like it. The sun stood out, clean-cut and vivid, on a
dark blue sky, and so slight were the traces of diffusion, that, for
observations at his edge the conditions approached those of a total
eclipse. These advantages are forcibly illustrated by the statement
that, instead of eight lines ordinarily visible in the entire spectrum
of the chromosphere, more than thirty revealed themselves in the orange
and green parts of it alone (Dto. F)! A fact still more remarkable is
that prominences were actually seen, and their forms distinguished,
though foreshortened and faint, on the very disc of the sun itself—and
this not merely by such glimmering views as had previously, at
especially favorable moments, tantalised the sight of Young and
Tacchini, but steadily and with certainty. We are further told that, on
the mornings of September 19th and 20th, Venus was discerned, without
aid from glasses, within two degrees of the sun.
These extraordinary facilities of vision disappeared, indeed, as, with
the advance of day, the slopes of the mountain became heated and set
the thin air quivering; but were reproduced at night in the tranquil
splendor of moon and stars.
The expediency of using such opportunities was obvious; and it has
accordingly been determined to erect a good equatorial in this tempting
situation, elevated 9,375 feet above the troubles of the nether air.
The expense incurred will be trifling; no special staff will be
needed; the post will simply constitute a dependency of the Paris
establishment, where astronomers thrown out of work by the malice of
the elements may find a refuge from enforced idleness, as well as,
possibly, unlooked-for openings to distinction.
We must now ask our readers to accompany us in one more brief flight
across the Atlantic. After a successful observation of the late transit
of Venus at Jamaica, Dr. Copeland, the chief astronomer of Lord
Crawford’s observatory at Dun Echt, took advantage of the railway which
now crosses the Western Andes at an elevation of 14,666 feet, to make a
high-level tour of exploration in the interests of science. Some of the
results communicated by him to the British Association at Southport
last year, and published, with more detail, in the astronomical journal
“Copernicus,” are extremely suggestive. At La Paz, in Bolivia, 12,050
feet above the sea, a naked-eye sketch of the immemorially familiar
star-groups in Taurus, _made in full moonlight_, showed seventeen
Hyades (two more than are given in Argelander’s “Uranometria Nova”)
and ten Pleiades. Now ordinary eyes under ordinary circumstances
see six, or at most seven, stars in the latter cluster. Hipparchus
censured Aratus—who took his facts on trust from Eudoxus—for stating
the lesser number, on the ground that, in serene weather, and in the
absence of the moon, a seventh was discernible.[26] On the other hand,
several of the ancients reckoned nine Pleiades, and we are assured that
Moestlin, the worthy preceptor of Kepler, was able to detect, under
the little propitious skies of Wurtemberg, no less than fourteen.[27]
An instance of keensightedness but slightly inferior is afforded by a
contemporary American observer: Mr. Henry Carvil Lewis, of Germantown,
Pennsylvania, frequently perceives twelve of this interesting sidereal
community.[28] The number of Pleiades counted is, then, without some
acquaintance with the observer’s ordinary range of sight, a quite
indeterminate criterion of atmospheric clearness; although we readily
admit that Dr. Copeland’s detection of ten in the very front of a full
moon gives an exalted idea of visual possibilities at La Paz.
During the season of _tempestades_—from the middle of December to
the end of March—the weather in the Andes is simply abominable. Mr.
Whymper describes everything as “bottled up in mist” after one brief
bright hour in the early morning, and complains, writing from Quito,
March 18th, 1880,[29] that his exertions had been left unrewarded by a
single view from any one of the giant peaks scaled by him. Dr. Copeland
adds a lamentable account—doubly lamentable to an astronomer in search
of improved definition—of thunderstorms, torrential rains merging
into snow or hail, overcast nocturnal skies, and “visible exhalations”
from the drenched pampas. At Puno, however, towards the end of March,
he succeeded in making some valuable observations, notwithstanding the
detention—as contraband of war, apparently—of a large part of his
apparatus. Puno is the terminal station on the Andes railway, and is
situated at an altitude of 12,540 feet.
Here he not only discovered, with a 6-inch achromatic, mounted as
need prescribed, several very close stellar pairs, of which Sir John
Herschel’s 18 inch speculum had given him no intelligence; but in
a few nights’ “sweeping” with a very small Vogel’s spectroscope,
he just doubled the known number of a restricted, but particularly
interesting, class of stars—if stars indeed they be. For while in
the telescope they exhibit the ordinary stellar appearance of lucid
points, they disclose, under the compulsion of prismatic analysis, the
characteristic marks of a gaseous constitution; that is to say, the
principal part of their light is concentrated in a few bright lines.
The only valid distinction at present recognisable by us between stars
and “nebulæ” is thus, if not wholly abolished, at least rendered of a
purely conventional character. We may agree to limit the term “nebulæ”
to bodies of a certain chemical constitution; but we cannot limit the
doings of Nature, or insist on the maintenance of an arbitrary line of
demarcation. From the keen rays of Vega to the undefined lustre of the
curdling wisps of cosmical fog clinging round the sword-hilt of Orion,
the distance is indeed enormous. But so it is from a horse to an oak
tree; yet when we descend to volvoxes and diatoms, it is impossible to
pronounce off-hand in which of the two great provinces of the kingdom
of life we are treading. It would now seem that the celestial spaces
have also their volvoxes and diatoms—“limiting instances,” as Bacon
termed such—bodies that share the characters, and hang on the borders
of two orders of creation.
In 1867, MM. Wolf and Rayet, of Paris, discovered that three yellow
stars in the Swan, of about the eighth magnitude possessed the notable
peculiarity of a bright-line spectrum. It was found by Raspighi and Le
Sueur to be shared by one of the second order of brightness in Argo
(γ Argûs), and Professor Pickering, of Harvard, reinforced
the species, in 1880-81, with two further specimens. Dr. Copeland’s
necessarily discursive operations on the shores of Lake Titicaca raised
the number of its members at once from six to eleven or twelve. Now the
smaller “planetary” nebulæ—so named by Sir William Herschel from the
planet-like discs presented by the first-known and most conspicuous
amongst them—are likewise only distinguished from minute stars by
their spectra. Their light, when analysed with a prism, instead of
running out into a parti-colored line, gathers itself into one or more
bright dots. The position on the prismatic scale of those dots, alone
serves to mark them off from the Wolf-Rayet family of stars. Hence the
obvious inference that both nebulæ and stars (of this type) are bodies
similar in character, but dissimilar in constitution—that they agree
in the general plan of their structure, but differ in the particular
quality of the substances glowing in the vast, incandescent atmospheres
which display their characteristic bright lines in our almost
infinitely remote spectroscopes. Indeed, the fundamental identity of
the two species are virtually demonstrated, by the “migrations” (to use
a Baconian phrase) of the “new star” of 1876, which, as its original
conflagration died out, passed through the stages, successively, of
a Wolf-Rayet or _nebular star_ (if we may be permitted to coin the
term), and of a planetary nebula. So that not all the stars in space
are suns—at least, not in the sense given to the word by our domestic
experience in the solar system.
The investigation of these objects possesses extraordinary interest.
As an index to the true nature of the relation undoubtedly subsisting
between the lucid orbs and the “shining fluid” which equally form part
of the sidereal system, their hybrid character renders them of peculiar
value. Their distribution—so far restricted to the Milky Way and its
borders—may perhaps afford a clue to the organisation of, and processes
of change in that stupendous collection of worlds. At present,
speculation would be premature; what we want are facts—facts regarding
the distances of these anomalous objects—whether or not they fall
within the range of the methods of measurement at present available;
facts regarding their apparent motions; facts regarding the specific
differences of the light emitted by them: its analogies with that
of other bodies; its possible variations in amount or kind. The
accumulation of any sufficient information on these points will demand
with every external aid, the patient labor of years; under average
conditions at the earth’s surface, it can scarcely be considered as
practically feasible. The facility of Dr. Copeland’s discoveries
sufficiently sets off the prerogatives, in this respect, of elevated
stations; it is not too much to say that this purpose—were it solely
in view—would fully justify the demand for their establishment.
Towards one other subject which we might easily be tempted to dwell
upon, we will barely glance. Most of our readers have heard something
of Dr. Huggins’s new method of photographing the corona. Its importance
consists in the prospect which it seems to offer for substituting
for scanty and hurried researches during the brief moments of total
eclipse, a leisurely and continuous study of that remarkable solar
appendage. The method may be described as a _differential_ one.
It depends for its success on the superior intensity of coronal
to ordinary sunlight in the extreme violet region. And since it
happens that chloride of silver is sensitive to those rays _only_ in
which the corona is strongest, the coronal form disengages itself
photographically, from the obliterating splendor which effectually
shrouds it visually, by the superior vigor of its impression upon a
chloride of silver film.
Now if this ingenious mode of procedure is to be rendered of any
practical avail, advantage must, above all, be taken of the finer air
of the mountains. This for two reasons. First, because the glare which,
as it were, smothers the delicate structure we want to obtain records
of, is there at a minimum; secondly, because the violet rays by which
it impresses itself upon the “photographic retina”[30] are there at a
maximum. These, as Professor Langley’s experiments show, suffer far
more from atmospheric ravages than their less refrangible companions
in the spectrum; the gain thus to them, relatively to the general
gain, grows with every yard of ascent; the proportion, in other words,
of short and quick vibrations in the light received becomes exalted
as we press upwards—a fact brought into especial prominence by Dr.
Copeland’s solar observations at Vincocaya, 14,360 feet above the
sea-level. Indeed, for all the operations of celestial photography, the
advantages of great altitudes can hardly be exaggerated; and celestial
photography is gradually assuming an importance which its first
tentative efforts, thirty-four years ago, gave little reason to expect.
Thus, in three leading departments of modern astronomy—solar physics,
stellar spectroscopy, and the wide field of photography—the aid of
mountain observatories may be pronounced indispensable; while in all
there is scarcely a doubt that it will prove eminently useful. There
are, indeed, difficulties and drawbacks to their maintenance. The
choice of a site, in the first place, is a matter requiring the most
careful deliberation. Not all elevated points are available for the
purpose. Some act persistently as vapor-condensers, and seldom doff
their sullen cap of clouds. From any mountain in the United Kingdom,
for instance, it would be folly to expect an astronomical benefit.
On Ben Nevis, the chief amongst them, a meteorological observatory
has recently been established with the best auguries of success; but
it would indeed be a sanguine star-gazer who should expect improved
telescopic opportunities from its misty summit.
Even in more favored climates, storms commonly prevail on the heights
during several months of the year, and vehement winds give more or less
annoyance at all seasons; the direct sunbeams sear the skin like a hot
iron; the chill air congeals the blood. Dr. Copeland records that at
Vincocaya, one afternoon in June, the black bulb thermometer exposed
to solar radiation stood at 199°.1 of Fahrenheit—actually 13° above
the boiling-point of water in that lofty spot—while the dry bulb was
coated with ice! Still more formidable than these external discomforts
is the effect on the human frame itself of transportation into a
considerably rarer medium than that for existence in which it was
constituted. The head aches; the pulse throbs; every inspiration is a
gasp for breath; exertion becomes intolerable. Mr. Whymper’s example
seems to show that these extreme symptoms disappear with the resolute
endurance of them, and that the system gradually becomes inured to its
altered circumstances. But the probationary course is a severe one;
and even though life flow back to its accustomed channels, labor must
always be painfully impeded by a diminution of the vital supply. And
the minor but very sensible inconveniences caused by the difficulty
of cooking with water that boils twenty or thirty degrees (according
to the height) below 212°, by the reluctance of fires to burn, and of
tobacco to keep alight, and we complete a sufficiently deterrent list
of the penalties attendant on literal compliance with the magnanimous
motto, _Altiora petimus_.
That they will, nevertheless, not prove deterrent we may safely
predict. Enthusiasm for science will assuredly overbear all
difficulties that are not impossibilities. Dr. Copeland, taking all
into account, ventures to recommend the occupation during the most
favorable season—say from October to December—of an “extra-elevated
station” 18,500 ft. above the sea, more than one promising site for
which might be found in the vicinity of Lake Titicaca. For a permanent
mountain observatory, however, he believes that 12,500 ft. would be the
outside limit of practical usefulness. It is probable, indeed, that
the Rocky Mountains will anticipate the Andes in lending the aid of
their broad shoulders to lift astronomers towards the stars. Already a
meteorological post has been established on Pike’s Peak in Colorado,
at an altitude of 14,151 ft. Telescopic vision there is said to be of
rare excellence; we shall be surprised if its benefits be not ere long
rendered available.
After all, the present strait of optical astronomy is but the
inevitable consequence of its astonishing progress. While instruments
remained feeble and imperfect, atmospheric troubles were comparatively
little felt; they became intolerable when all other obstacles to a vast
increase in the range of distinct vision were removed. The arrival of
that stage in the history of the telescope, when the advantages to be
derived from its further development should be completely neutralised
by the more and more sensibly felt disadvantages of our situation on an
air-encompassed globe, was only a question of time. The point was a
fixed one: it could be reached later only by a more sluggish advance.
Both the difficulty and its remedy were foreseen 167 years ago by the
greatest of astronomers and opticians.
“If the theory of making telescopes,” Sir Isaac Newton
wrote in 1717,[31] “could at length be fully brought into
practice, yet there would be certain bounds beyond which
telescopes could not perform. For the air through which we
look upon the stars is in a perpetual tremor as may be seen
by the tremulous motion of shadows cast from high towers,
and by the twinkling of the fixed stars. The only remedy is
a most serene and quiet air, such as may perhaps be found
on the tops of the highest mountains above the grosser
clouds.”
—_Edinburgh Review_.
GOETHE
BY PROF. J. R. SEELEY.
III.