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IX. DETHRONING TENNYSON,

X. ATMOSPHERIC CURIOSITIES,.

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XII. ICE-BOATING IN THE GULF OF FINLAND, Manchester Guardian,

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For EIGHT DOLLARS, remitted directly to the Publishers, the LIVING AGE will be punctually forwarded for a year, free of postage.

Remittances should be made by bank draft or check, or by post-office money-order, if possible. If neither of these can be procured, the money should be sent in a registered letter. All postmasters are obliged to register letters when requested to do so. Drafts, checks, and money-orders should be made payable to the order of LITTELL & Co.

Single Numbers of THE LIVING AGE, 18 cents.

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A TRANSLATION.

AN ANONYMOUS MODERN GREEK SONG.
COULD you ever near me be
What a blissful life of gladness!
But to part so tries the heart,
Fills it with such utter sadness!
Yet, love, when far from thee,
Why is life, ah! why is life still dear to me?
Just a ring of braided hair
Is the only gift remaining.
Nothing else can comfort me,
Lustreless yet love-retaining.
And yet so far from thee

Why live longer? Life no more is dear to me!
Academy.
GEORGE GORDON HAKE.

From The Edinburgh Review.
SIDEREAL PHOTOGRAPHY.*

Celestial photography, as was natural, made its first essay with the moon. The broad, mild face of our satellite, diversified with graduated lights and intense shadows, formed a tempting subject for the nascent art. At Arago's suggestion, accordingly, Daguerre exposed one of his sensitive plates to the lunar rays, but with a disappointing result. Nothing worthy the name of a picture made its appearance. Professor J. W. Draper, of New York, however, obtained early in 1840 some little prints, not altogether characterless, of the lunar surface, after which

THE application of photography to astronomical research is rapidly transforming its destinies. The more closely the exquisite sky-prints recently taken at Paris and elsewhere are studied, the more opulent of promise they appear. Their pictorial beauty is the least of their merits. In the eyes of the astronomer their eminent value lies in their capability of exact measurement. Upon this basis of fact rest anticipations which to unaccustomed ears sound exaggerated, but which the future will, unless we are much mistaken, the subject dropped out of sight during amply justify. We can have no hesitation in admitting that what has been done, not by chance, but on system, can be done again. Results already obtained can be repeated and multiplied. It needs no more—although much more will probably be accomplished · to ensure a new birth of knowledge regarding the structure of the universe.

ten years, It was resumed at Harvard College Observatory by George P. Bond, one of whose lunar daguerreotypes attracted deserved attention at the Great Exhibition in 1851. The light employed to produce them was concentrated by a telescope fifteen inches in aperture, equatorially mounted, and kept fixed by a clockwork movement upon the moving object to be depicted.

The scientific importance of Daguerre's invention was perceived from the outset. Bond's pictures marked the close of the In formally announcing it to the Academy first or tentative period in celestial photogof Sciences, August 19, 1839, Arago char-raphy. In 1851 the collodion process was acterized it as "a new instrument for the introduced by Frederick Scott Archer, study of nature," the manifold uses of and rapidly superseded all others. Dawhich must baffle, and would assuredly guerreotypes, lunar, solar, and terrestrial, surpass, prediction. "En ce genre," he began to assume an antiquarian interest added significantly, "c'est sur l'imprévu and aspect. qu'on doit particulièrement compter." † And it is indeed the unforeseen which has come to pass. Arago himself, with all his readiness to admit incalculable possibilities, would have been staggered by a forecast of the work now actually of light by impregnation with salts of being done. silver. The sensitiveness of these subLa Photographie Astronomique à l'Observa-stances is due to their possessing a motoire de Paris et la Carte du Ciel. Par M. le Contre-lecular equilibrium so delicate as to be

I.

Amiral E. MoUCHEZ. Paris: 1887.

2. An Investigation in Stellar Photography conducted at the Harvard College Observatory. By EDWARD C. PICKERING. Cambridge, U.S.: 1886.

3. First Annual Report of the Photographic Study of Stellar Spectra conducted at the Harvard College Observatory. By EDWARD C. PICKERING, Director. Cambridge, U.S.: 1887.

4. The Applications of Photography in Astronomy. Lecture delivered at the Royal Institution, Friday, June 3, 1887. By DAVID GILL, LL.D., F.R.S. (The Observatory, July and August, 1887.)

5. Die Photographie im Dienste der Astronomie. Von O. STRUVE. (Bulletin de l'Académie Impériale

des Sciences de St.-Pétersbourg, Tome xxx. No. 4: 1886.)

† Comptes Rendus, tome ix., p. 264.

Collodion is a colorless, semi-viscous fluid produced by dissolving gun-cotton in a mixture of alcohol and ether. Spread upon glass, it forms a transparent membrane rendered susceptible to the action

overturned by the quick ethereal impacts of the vibrations of violet light. The metal they contain, thus partially released from the bonds of chemical combination, is ready to attract further deposits; and the opportunity of exercising this power of appropriation is afforded by the processes of development.* A photograph is hence a picture painted in metallic silver under the regulating influence of light.

Some kinds of development merely complete the "reducing" process begun by the action of light, without adding any fresh metallic supplies.

Mr. Warren De la Rue was the first to turn Archer's improvement to account for astronomical purposes. He began his photographic work towards the close of 1852 with a thirteen-inch reflector of his own construction which gave him successful pictures of the moon, one inch across, in ten to thirty seconds. Some taken later with improved means bore enlargement to eight inches, and clearly showed details representing an actual area on the moon's surface of about two and a half square miles. The distribution of light and shade in them differed so notably from that perceived with the eye as to afford hints (it was thought) towards a science of lunar geology, formations of different epochs being distinguished by their varying powers of reflecting the actinic rays. The marked deficiency in chemical power of the so-called "seas," in especial, suggested that they might in reality be plains clothed with vegetation, the vital needs of which were supplied by a dense, low-lying atmosphere.

*

Mr. De la Rue showed further that, by the stereoscopic combination of two photographs taken at opposite phases of the moon's libration, something might be learned as to the relative age of lunar craters. The deep furrows diverging from Tycho, for instance, were perceived to run right through some craters, but to be overlaid by others.† Obviously, then, the dislocated craters were already in exist ence when these clefts opened, while the unaffected ones were of later production. With the improved photographic methods now in use, it is quite possible that the real position in Jupiter's atmosphere of the great red spot adhering to his southern belt may in this way be determined; perhaps even indications derived as to the nature of the mysterious Martian canals.‡ The immediate followers of De la Rue in lunar photography were two gifted Americans, Dr. Henry Draper and Lewis M. Rutherfurd of New York. The moon,

Report British Association, 1859, p. 145. † Monthly Notices, vol. xxiii., p. 111.

The rotation of the planets gives the differences

in the point of view requisite for obtaining stereoscopic relief. Photographs taken at intervals-for Jupiter of twenty-six, for Mars of sixty-nine minutes-combine with the proper effect. (De la Rue, Report Brit. Ass., 1859, p. 148.)

as seen with the naked eye, is about onetenth of an inch in diameter; that is to say, it is just covered by a disc of that size held at the ordinary distance for clear vision.* One of Draper's pictures, taken with a fifteen-inch silvered glass reflector, September 3, 1863, and subsequently enlarged, showed it as three feet across, or on a scale of about sixty miles to the inch. The spectator was virtually transported to a point six hundred miles from the lunar surface.

Reflectors possess the great advantage of being perfectly achromatic; undulations of all wave-lengths are collected by them at a single focus. In refractors, on the other hand, there is always a certain amount of dispersion. Opticians have to choose which rays to unite, leaving the others to shift for themselves. They in general, of course, bestow exclusive attention on those of greatest visual intensity. Ordinary achromatics have hence no sharp chemical focus. Rutherfurd,, however, took the more rapid vibrations alone into account in calculating the curves of an object-glass of eleven inches designed expressly for photographic use. He thus set the example of deliberately constructing a telescope totally unserviceable to the eye. By its means were obtained in 1865 lunar photographs which marked the culmination of the art in its second, or "wet-collodion," stage.

Yet the result, striking as it was in some respects, somewhat disappointed expecta tion in others. The details of structure were not so distinctly given as to serve for a criterion of future change; nor has any lunar photograph yet taken shown the crispness of the best telescopic views. The reason is obvious. Atmospheric shiverings, which the eye can to some extent eliminate, produce their full effect on the sensitive plate. The resulting picture is the summation of a multitude of partial impressions due to evanescent distortions and displacements of the image.

It was perhaps owing to a sense of partial failure that lunar photography fell into neglect during twenty years. Now at last there are signs of revived interest in it. Recent improvements afford great advan

H. Draper, Quart. Jour. of Science, vol. i., p. 381.

tages for its cultivation. Owing to the high sensitiveness of modern plates the images thrown upon them can be strongly magnified, while the time of exposure is still kept extremely short. The MM. Henry have accordingly adopted the plan of photographing the moon in sections, six or eight of which cover the visible hemisphere, and are united to form a map one and a half to two feet in diameter. A repetition of the process at intervals will test the occurence of variations in lunar topography extending over not less than one and a half square miles.

but distinct impression of the corona during the total eclipse of July 28, 1851. But the triumph of practically establishing the value of photography as a means of investigating the solar appendages was reserved for Mr. De la Rue and Father Secchi. By the comparison of photographs taken at various stages of the eclipse of July 18, 1860, the status of the "red protuberances was settled forever. The advance of the moon over them proved beyond cavil that they belonged to the sun.

The camera is an encroaching instrument. So surely as it gains a foothold in The finest telescope in the world for the any field of research, so surely it advances purposes of moon-portraiture is undoubt to occupy the whole, either as adjunct or edly the giant refractor of the Lick Observ-principal. Telescopic and direct spectroatory in California. With an aperture of scopic observations during solar eclipses three and a focal length of fifty feet, it are now altogether subordinate in imporgives a direct image of the moon six inches tance to photographic records of them. in diameter, negative impressions of which Fleeting appearances, likely either to esmay be enlarged with advantage to per- cape or to mislead the eye during the haps twelve feet. But the third lens, by lapse of those counted and crowded mowhich the correction of this superb instru- ments, are stored up for leisurely interprement can be modified at pleasure to suit tation; and the whole working power of the actinic rays, has yet to be provided; the mind can thus be devoted to the coland perfect glass discs of thirty-six inches lection of materials for subsequent discusare not to be had for the asking. They sion. The discovery of a comet close to may be bespoke a long time before they the sun, May 17, 1882, is a picturesque inare forthcoming. cident of eclipse-photography. "Tewfik," as the object was named in compliment to the reigning khedive, made its first known appearance to terrestrial spectators during the seventy-four seconds of total obscurity at Sohag. It was caught with beautiful distinctness on Dr. Schuster's plates of the corona, and its place was measured from them; but, for lack of previous or subsequent observations, it must forever remain unidentified.

The sun can now be photographed in the inconceivably short space of the one hundred thousandth part of a second.* A short exposure, followed by a long and strong development, gives the best results; and it is difficult to see how those obtained by M. Janssen at Meudon during the last eight or nine years can be much improved upon. It might, however, be found possible to work on a larger scale. Advantage for the exhibition of details would probably be derived from the use of a solar image more highly magnified than has hitherto been customary.

The historical starting-point of solar photography is a daguerreotype taken at Paris by MM. Foucault and Fizeau, April 2, 1845. The attempt, though not unsuccessful, remained isolated for a number of years. The eclipsed sun was the subject of the next experiment. Busch and Berkowski of Königsberg obtained a slight • Janssen, Annuaire du Bureau des Longitudes,

1883, p. 809.

But we must hurry on, lest time fail us to describe the latest developments of this marvellous art. They are due to improvements of a fundamental kind in photographic processes. Collodion-plates can practically only be used in a wet state. This narrowly limits the time of exposure. Moreover, the preparation of each plate must immediately precede and its development immediately follow exposure — conditions which inconveniently hamper the operations of the astronomical photographer. In 1871, however, gelatine was by Dr. R. L. Maddox substituted for collo

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