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 nebulae, 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.