During the last few years, or rather decades of years, it has become
rather a trite saying that to advance far in any branch of physical
research a fair proficiency in no inconsiderable number of the sister
sciences is an absolute necessity. But if this is true in general, none, I
think, will question the assertion that a proficient in any of the
physical sciences must be fairly conversant with photography as a science,
or at least as an art. If we take for example a science which has of late
years made rapid strides both in Europe and America, the science of
astronomy, we shall not have far to go to find convincing proof that a
great portion of the best work that is being done by its votaries is
effected by the aid of photography. One eminent astronomer has quite
lately gone so far as to declare that we no longer require observers of
the heavens, but that their place can be better supplied by the gelatine
plate of the photographer; and his words have been echoed by others not
less able than himself. "Abolish the observer, and substitute the
sensitive plate," is a sensational form of expressing the revolution in
observational astronomy that is taking place under our eyes; but, although
it suggests a vast amount of truth, it might leave upon the mind an
exaggerated impression inimical to the best interests of science.
The award of the highest distinction in astronomy, the gold medal of the
Royal Astronomical Society, two years in succession, to those who have
been most successful in celestial photography is no doubtful sign of the
great value attached to such work. Last year it was Mr. Common who
received the highest testimony of the merit due to his splendid
photographs of the nebula of Orion; and this year Dr. Huggins, who has
drawn much attention to celestial photography, by his successful attempts
to picture the solar corona in full daylight, has received a similar
acknowledgment of his labors in photographing the spectra of stars and
comets and nebulæ.
An adequate idea of the progress astronomy is now making by aid of
photography can only be formed by a comprehensive view of all that is
being at present attempted; but a rapid glance at some of the work may
prepare the way for a more thorough investigation. A few years since, the
astronomers who had advanced their science by aid of photography were few
in number, and their results are soon enumerated. Some good pictures of
the solar corona taken during solar eclipses, a series or two of sun-spot
photographs, and a very limited number of successful attempts made upon
the moon, and planets, and star clusters, were all the fruits of their
labors. But now each month we learn of some new and efficient laborer in
this field, which gives promise of so rich a harvest.
Each day the sun is photographed at Greenwich, at South Kensington, in
India, and at the Physical Observatory of Potsdam, and thus a sure record
is obtained of all the spots upon its surface, which may serve for the
study of the periodicity of its changes, and for their probable connection
with the important phenomena of terrestrial magnetism and meteorology. In
France the splendid sun-pictures obtained by Dr. Janssen at the Physical
Observatory of Meudon have thrown into the shade all other attempts at a
photographic study of the most delicate features of the solar surface.
Dr. Huggins has shown that it is possible to obtain a daily photographic
record of the solar prominences, and only lately he has secured results
that justified a special expedition to the Alps to photograph the sun's
corona, and he has now moved the Admiralty to grant a subsidy to Dr. Gill,
the government astronomer at the Cape, by aid of which Mr. Woods can carry
on the experiments that were so encouraging last summer in Switzerland.
We may, then, reasonably hope to obtain before long a daily picture of the
sun and a photographic record of its prominences, and even of a certain
portion of the solar corona; but the precious moments of each solar
eclipse will always be invaluable for picturing those wondrous details in
the corona that are now shown us by photography, and which can be obtained
by photography alone.
Again, how very much is to be learnt in solar physics from the marvelous
photographs of the sun's spectrum exhibited last summer by Professor
Rowland; photographs that show as many as one hundred and fifty lines
between H and K, and which he is still laboring to improve! The extension,
too, of the visible solar spectrum into the ultra-violet by Corun,
Mascart, and others, adds much to our knowledge of the sun; while the
photographs of Abney in the ultrared increase our information in a
direction less expected and certainly less easy of attainment. Both these
extensions we find most ably utilized in the recent discussion of the very
interesting photographs of the spectra of the prominences and of the
corona taken during the total eclipse of May 18, 1882; and the
photographic results of this eclipse afford ample proof that we can not
only obtain pictures of the corona by photography that it would be
impossible otherwise to procure, but also that in a few seconds
information concerning the nature of the solar atmosphere may be furnished
by photography that it would otherwise take centuries to accumulate, even
under the most favorable circumstances.
The advantages to be gained by accurate photographs of the moon and
planets, that will permit great enlargements, are too obvious to call for
lengthened notice in such a rapid sketch as the present; for it is
principally in the observation of details that the eye cannot grasp with
the required delicacy, or with sufficient rapidity, that photography is so
essential for rapid and sure progress.
Like the sketches of a solar eclipse, the drawings that are made of
comets, and still more of nebulæ, even by the most accomplished artists,
are all, to say the least, open to doubt in their delicate details. And
the truth of this is so obvious, that it is the expressed opinion of an
able astronomer that a single photograph of the nebula of Orion, taken by
Mr. Common, would be of more value to posterity than the collective
drawings of this interesting object so carefully made by Rosse, Bond,
Secchi, and so many others.
Another most important branch of astronomy, that is receiving very great
attention at present, is the mapping of the starry heavens; and herein
photography will perhaps do its best work for the astronomer. The trial
star map by the brothers Henry, of a portion of the Milky Way, which they
felt unable to observe satisfactorily by the ordinary methods, is so near
absolute perfection that it alone proves the immense superiority of the
photographic method in the formation of star maps. Fortunately this
subject, which is as vast as it is fundamental, is being taken up
vigorously. The Henries are producing a special lens for the work; Mr.
Grubb is constructing a special Cassgrain reflector for Mr. Roberts of
Maghull; and the Admiralty have instructed Mr. Woods to make this part of
his work at the Cape Observatory, under the able direction of Dr. Gill.
Besides star maps, clusters, too, and special portions of the heavens are
being photographed by the Rev. T.E. Espin, of West Kirby; and such
pictures will be of the greatest value, not only in fixing the position at
a given date, but also aiding in the determination of magnitude, color,
variability, proper motion, and even of the orbits of double and multiple
stars, and the possible discovery of new planets and telescopic comets.
Such are some of the many branches of astronomy that are receiving the
most valuable aid at present from photography; but the very value of the
gift that is bestowed should make exaggeration an impossibility.
Photography can well afford to be generous, but it must first be just, in
its estimate of the work that has still to be done in astronomy
independently of its aid; and although the older science points with just
pride to what is being done for her by her younger sister, still she must
not forget that now, as in the future, she must depend largely for her
progress, not only on the skill of the photographer and the mathematician,
but also on the trained eye and ear and hand of her own indefatigable
observers.--_S.J. Perry, S.J., F.R.S., in Br. Jour. of Photography._
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