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The photographic news
- Bandzählung
- 27.1883
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- 1883
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- Bandzählung
- No. 1286, April 27, 1883
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The photographic news
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Band 27.1883
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- Titelblatt Titelblatt I
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Band 27.1883
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THE PHOTOGRAPHIC NEWS. Vol. XXVII. No. 1286.—April 21, 1883. CONTENTS. The Eclipse of May 15, 1882 257 Laryngeal photography 258 Typographic Blocks from Ordinary Negatives 258 Comparing the Sensitiveness of Different Plates 260 The Causes of the Discolouration of Iodised Collodion, and its Intensity-giving Properties 261 By-the-Bye.—Fancy Card Mounts 261 Gelatine v. Collodion. By Charles Ehrmann 263 Notes 263 PAGE Patent Intelligence : 263 “ How No. 1 was Taken.” By Henry Dixon........................ 236 Photo-Lithography and Photo-Zincography. By Major J. Waterhouse, fe.S.C 267 The Eclipse Expedition. By 0. Ray Woods 268 Correspondence 26% Proceedings of Societies 270 Talk in the Studio 272 To Correspondents 272 THE ECLIPSE OF MAY 15, 1882. It is now more than a year since the public were kept alive as to the fact that a total eclipse was to be visible in Egypt on the 15th of last May, and that astronomers from France, Italy, and England were to be sent to observe it. The questions, amongst others, to be solved during such phenomena, are those relating to the constitution and origin of thebright prominences which reach above the solar photosphere, and also to fathom the limits of the corona, halo, or glory which surrounds the sun, which can only be seen when the fiery disc itself is cut off by the inter position of the moon as a screen. Since this screen is beyond our atmosphere, direct solar rays cannot get dis persed in it. Thus we are allowed to see with facility this comparatively faint light, which at ordinary times is im possible owing to the glare of ordinary skylight. Hence it is that astronomers have taken advantage of every pos sible opportunity to observe an eclipse, and from 1865 have used photography as an aid. The advent of gelatine plates, amongst other things, has rendered it imperative to continue these observations ; and though some have asserted that eclipses are played out, yet it is evident from the summary below of a paper read by Dr. Schuster and Captain Abney at the Royal Society in April, that this is far from the case. They confined themselves to describing the results ob tained by means of photography. The instruments used were as follows :—An ordinary camera with a lens of 4-inch aperture, and 5 feet 3 focal length; a prismatic camera— that is, a camera with a prism in front of the lens, or, in other words, a spectroscope without a collimator. The refracting angle of the prism, which had a 3-inch square face, was 60°, and a photographic spectroscopic with one prism having a refracting angle of 62°, and a length of collimator and camera of 9 inches. Three photographs of the corona, having exposures of three, eleven, and twenty-three seconds respectively, were obtained with the first instrument. The photographs show the prominences very well, and confirm the distinction which has been made between the inner and outer corona. The photographic impression of one of the rifts or streamers which are so markedly seen in nearly all coronas, reached to a distance of 14 solar diameter away from the sun’s limb, and as regards form and general appearance, the most remarkable point is the curvature of these rays, and the structural detail visible in one streamer and overlapped by another. The comet which was seen close to the sun, which drew such attention at the time of the eclipse, is also sharply de fined on all the plates, and it seems to have had a per ceptible motion even during the one minute’s duration of the eclipse, judging by its measures from the moon’s centre, taken from the three photographs. The comet was christened Tewfik by the assembled astronomers, after the Khedive, whose guests they were during their sojourn in Egypt. With the prismatic camera, which gave rings of prominences corresponding to the different rays which they emitted, some remarkable results have also been obtained. Amongst other things, it was proved that some prominences were hotter than others, and that some had lines below the red, for the plates used with this instrument were sensitive to this region, and had been specially pre pared by Captain Abney for it. Another point which this photograph settles is, that the layer of heated vapour in proximity to the sun's limb is made up of some stuff which radiates a ray in the green and a ray in the orange, known respectively as 1474 and Da ; the latter is much fainter than the former. An instantaneous photograph, taken with this prismatic camera five seconds after totality was over, also gives the prominences, showing that sun light had not then overpowered the prominence light. A photograph taken with the spectroscopic camera has, perhaps, yielded the most valuable results. The corona seems to have a continuous spectrum near the sun, and beyond that the spectrum is resolved into lines, not coinciding with the prominence lines, but totally distinct. Formerly but one line, 1474, above alluded to, was known as a coronal line; but from the photograph, measures of thirty-one lines have been obtained from the green to the ultra violet of the spectrum. Thollon noted several in the violet, but was unable to fix their wave length, showing the great value a photograph has over eye observations when time is limited. The photo graph also shows that the outer corona shines partially with reflected light, as the ordinary solar spectrum was photographed in the violet (to which region the plates were most sensitive) very faintly, and nearly a sun’s diameter distant from the moon’s edge. It was pointed out that the prominence spectrum of the sun corresponds very closely with the spectra of some of the stars photographed by Dr. Huggins, and this, perhaps, opens out a new vista of research. It should be remarked that twenty-nine prominence lines have been photographed, including all the hydrogen lines known from the red to the ultra violet, and many of the calcium lines. That calcium is strongly existent in the solar photosphere is shown by the fact that the calcium lines were so strong that they illuminated the atmosphere between the dark moon and the observers, as the calcium bright lines are seen to extend across the otherwise black spectrum of the moon. This was shown in the photograph taken with the ordinary spectroscopic camera, where the image of the dark moon and the corona was cast by a lens on the slit, and a disc of the image passed through the prisms as in the accom panying figure. It is evident that if there were no light on the moon’s image, the spectrum between a and b would
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