The photographic news

• Bandzählung: 35.1891
• Erscheinungsdatum: 1891
• Sprache: Englisch
• Signatur: F 135
• Vorlage: Hochschule für Grafik und Buchkunst Leipzig
• Digitalisat: Hochschule für Grafik und Buchkunst Leipzig
• Digitalisat: SLUB Dresden
• Rechtehinweis: Public Domain Mark 1.0
• URN: urn:nbn:de:bsz:14-db-id1780948042-189100009
• PURL: http://digital.slub-dresden.de/id1780948042-18910000
• OAI: oai:de:slub-dresden:db:id-1780948042-18910000
• Sammlungen: LDP: Historische Bestände der Hochschule für Grafik und Buchkunst Leipzig
• Sammlungen: Fotografie
• Strukturtyp: Band

• Digitalisat: SLUB Dresden
• Strukturtyp: Ausgabe

bers." In an able paper lately published by Mr. Common, we learn that the aperture of the refracting telescope has greatly increased. In 1863 Cooke completed the 25-inch refractor now in the possession of the Cambridge Univer sity. Alvan Clark manufactured the 36-inch telescope lately erected at Mount Hamilton, California, under the direction of Professor Holden. The reflecting telescope has grown pari passu with its elder brother. In France there is one of four feet at the Paris Observatory. In England, too, this form of telescope is largely used, and, says Mr. Common, mirrors up to five feet in diameter have been made and mounted equatorially. Reflecting telescopes give images absolutely achromatic, but their mounting is less perfect than that of the refracting. “It is well known,” says Dr. Duner, the astronomical professor in the Swedish University of Upsala, “ that the subjects of photographic portraiture are either self-illu mined, or so strongly lighted that their reflected rays are able to reproduce their picture.” To show, by means of photography, the existence of a heavenly body which can produce no impression upon the bromide silver gelatine has been reserved for the present time. As long as two hundred and twenty years ago, it has been known that there was great variation in the degree of light emitted by the star Algol (5 Persei) in the head of Medusa. The Arabs call the head of Medusa held by Perseus the head of the ghoul, a malignant supernatural demon of variable form devouring men and well known to the readers of the Arabian Nights. The marked fluctuations of light in this member of the constellation of Perseus was already noticedin 1669 by Montanari. Algol is indeed the lead ing light of a small group containing about a hundred of so-called variable stars. Amongst these, after Algol, Mira (o Ceti) and (" Argus), of the southern hemisphere’ exhibit variations of the most extraordinary character. Mira in Cetus, so called from this peculiarity, appears at its brightest of the second magnitude, whence it gradu ally wanes to the twelfth, and then increases to its former splendour. An interval of some 330 days occurs between its periods of greatest brightness. Algol is best seen on the early evenings. In autumn, after sunset, it shines low down in the north-east of the heavens, in spring low down on the north-west, and in winter it flashes high in the north, not far from the zenith. The variations of its radiance were first accurately observed in 1782, when it was shown that its light was constant and steady as that of a star of the second magnitude for 2 days, 20 hours, and 49 minutes, after which it gradually faded till it reached a minimum, or that of a star of the fourth magnitude, in 4} hours, recovering its original splendour in 4 hours. Of this change of 9} hours, only about 5 hours is distinctly perceptible. The diminution of light is also strictly impartial. Its pure white radiance is the same in kind, however decreased in quantity. Professor Vogel, of the Astrophysical Observatory of Potsdam, has shown by the spectrograph that the old hypothesis of the cause of the change of light in Algol is undoubtedly true, and that Algol is a double star consisting of a light star of 1,725,000 kilometres diameter, and a dark of 1,350,000, of which the former weighs four-ninths, and the latter two-ninths of the sun, while they are at a distance from one another of 5} million kilometres, or one-tenth of the distance of Mercury from the sun. Vogel has also, by the aid of the camera, determined the velocity of some of the so-called fixed stars. Of course fewer waves of light enter the eye in a given time as the star recedes, and more as it approaches. This causes a shifting of the lines in the spectrum of the star’s light, which can be photographed. It is hardly necessary to add, except for those whose knowledge of astronomy is represented by Miss Taylor’s hymn, that this light is not of the present but of the past. Photographs of the great nebula of Orion show the light of that nebula, sup posing it not to be absorbed in any degree in space, as it was not less than sixty thousand years ago. All that vast period of time has been consumed in its attempt to penetrate that which intervenes between us and it, and its shaken splendour is probably due to the difference of velocity of rays traversing strata unequally warm or unequally cold, unequally humid or unequally dry. To judicial astrology the science of photography has aided other sciences to administer a destructive stroke. The faithlessness of our later age attributes no more virtue to Antares (a Scorpionis), the scorpion’s heart and the red rival of Mars, or to Rigel (B Orionis). which derives its name from its situation in the left foot of that strangely generated giant, than, as Burton complained in his own time, to the signs at an inn-keeper’s post or a tradesman’s shop. The great book in whose flaming letters are written, if we may believe ancient learning, so many strange things for such as are able to read them; that excellent harp made by an eminent workman, on which he that can but play will make most admirable music—both are still studied, but in a fashion far different from that of yore. The pictorial stellar maps of Ptolemy’s Almagest have given place to the Sternverzeichniss of Argelander. The animal configu rations attributed to the heroic age excite now only a lukewarm interest; but the method of Bayer of Augsburg, involving the use of the Greek and Roman alphabets, in vented more than two and a-half centuries ago, is now fast attaining universal learned recognition. If all these matters are too recondite to attract the public interest, the popular eye may delight itself with pictures of Cygnus and the Pleiades taken at Paris by the brothers Henry, and by slides of Jupiter and Saturn taken by Pickering in America; by the details of the ncbul of Orion and Andromeda revealed by Common and Roberts, and by a photographic survey of the whole southern hemi sphere by Dr. Gill, of the Observatory at Cape Town. Thus may the observer learn to appreciate that picture of the entire sky proposed by Admiral Mouchez, when the good time arrives of its realization. Photography has already done astronomy yeoman’s service, and gives rich promises of doing still more. The new method of investigation has not only greatly lessened the difficulty of variable stars of the Algol type, and generally increased our knowledge of double stars ; it has also acquainted us with the diameter and weight of fixed stars, concerning which subjects, except with regard to our own sun, the world hitherto has been wholly ignorant. Limit of Magnification for Photo-Micrography.—Mr. Nelson, says the Journal of Microscopy, puts this at 1,000. He has reached 1,500, and, in special instances, even 1,650 ; but he regards 1,000 as a useful limit. This can be obtained by an inch objective, with an eye-piece giving twenty times the initial power of the lens. Friedrich Jamrath.—The Photographische Nachrichten of March 26th records the death on the 19th inst., after a short illness, in his eighty-first year, of Friedrich Jamrath, portrait painter and Court photographer at Berlin. The deceased had I been a zealous member of the Photographischen Vereins zu I Berlin from its establishment,