Towler, John. The Silver Sunbeam.
Joseph H. Ladd, New York: 1864. Electronic edition prepared from
facsimile edition of Morgan and Morgan, Inc., Hastings-on-Hudson,
New York. Second printing, Feb. 1974. ISBN 871000-005-9
WITHIN the last few years the importance of the application of
photography to astronomical investigations, as well as to
meteorology, has been recognized by natural philosophers as a
definite help-mate in the prosecution of these studies. This
application consists, when referred to astronomy, in obtaining
photographs and stereographs of the moon in its various phases, of
the sun, of the planets, and of the comets; and, when referred to
meteorology, in obtaining photographic delineations of the different
classes of clouds; of the aurora borealis in its various
configurations, of meteors, halos, water-spouts, paraselenes,
For this purpose the various forms of telescopes, both reflecting
and refracting, may be employed, which are used in observatories.
Refracting telescopes, from the fact of their objectives being
corrected for the luminous part of the spectrum, are far from being
corrected for photographic purposes; and the ground glass has
sometimes to be moved as much as an inch from the position of the
luminous focus before the actinic focus is arrived at. Reflecting
telescopes, on the contrary, not decomposing light, have to undergo
no correction for actinism. For amateur astronomical photographers
silvered glass mirrors, as recommended by Steinheil, are most easily
constructed, are comparatively cheap, and from their lightness very
manageable. These, when properly mounted, will give a picture of the
moon, etc., of a magnitude varying with the focal length of the
mirror. The ground glass is placed in the principal focus of the
objective or reflector, and has a motion by which it can be adjusted
to accuracy. In such cases the eye-pieces are removed. When the
operation is not instantaneous, the telescopes have to be furnished
with clock-work, by means of which the axis of the body photographed
can always be made to coincide with the axis of the telescope,
during the time of exposure.
We are indebted to Messrs. Bond of Cambridge, Crookes, De la Rue,
Hartnup, Forrest, Edwards, Berry, Hodgson, Secchi, etc., for
interesting information and photographs of celestial objects.
The moon naturally claimed the first attention; the Bonds were
the first to obtain a daguerreotype of this satellite; Messrs.
Hartnup, Forrest, Berry, and Edwards obtained very beautiful
photographs on collodion of the moon in 1854, of an inch and one
third in diameter, which they afterward magnified a few diameters on
another collodion plate, and then exhibited the photographic
representation on a large screen sixty feet in diameter, the picture
having been magnified to this extent by means of a magic
At the same time Mr. Hartnup suggested a plan of taking a
stereograph of the moon, by first taking a photograph of this
luminary twelve hours before full, and then twelve hours after full,
thus changing the shadows from one side. to the other. The
stereograph was successful, and exhibited the moon in relief. From
the fact that the moon revolves on her axis in the same period that
she revolves in her orbit, it is difficult to obtain a degree of
parallax by which more of one side can be seen at one time than at
another; but the axis of the moon, that is, the moon itself in the
direction of its axis, has a sort of libration, which brings to
light alternately more of the northern parts than of the southern.
By taking photographs at these different periods a sufficient amount
of parallactic angle has been obtained, and perfect stereographs
have been the result. The moon has been photographed and
stereographed in all her phases; the shadows of the mountains are so
well delineated in these different phases as to admit an accurate
measurement of the height and diameter of those mountains.
A few seconds' exposure with a good equatorial will, in general,
give a tolerable negative. It is not absolutely necessary to be
furnished with a telescope in order to get a photograph of the moon;
the photographer will be glad to learn that a long-focussed
view-tube will permit him to obtain a copy of this bright luminary,
of about half an inch in diameter, which can afterward be magnified
to any size desired. The only difficulty is to keep the moon in
exactly the same position of the ground glass for a number of
The sun is easily photographed, because the operation is
instantaneous. The act of focussing is performed by placing a piece
of violet-colored glass over the opening of the objective, which is
retained there during the exposure. In this way eclipses of the sun
can be photographed without that immense trouble and risk which have
been so often referred to in celestial photography.
The stars have a high degree of photogenic power, and can be
photographed in accordance with the intensity of their light. Mr.
Bond has endeavored to base upon this power a means of classifying
the stars into magnitudes, which at present are quite arbitrary.
The planets, possessing much less photogenic power than the fixed
stars, are in consequence not so easily photographed; but by means
of well-regulated clock-work, De la Rue has succeeded in obtaining
very excellent photographs of Jupiter and his bands, Saturn and his
rings, as also a stereograph of Mars, by taking two photographs at
an interval of two hours, and others of Saturn at an interval of
three years and a half.
It is supposed there are planets nearer to the sun than Mercury,
which have not been discovered by reason of their proximity to the
solar orb: it is hoped, however, by means of photography to settle
this supposition; for if at any time in any of the numerous
photographs which are taken of the sun, a small, round black speck
should be discovered, the conclusion of the existence of another
inferior planet would soon be drawn.
De la Rue is prosecuting this branch of photography and astronomy
with great zeal and success; his labors, too, are highly
appreciated. The Astronomical Society of London have conferred upon
him their annual large medal as a token of their high appreciation
of his merits and the results of his labors.