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The photographic news
- Bandzählung
- 27.1883
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- 1883
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- Englisch
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- Hochschule für Grafik und Buchkunst Leipzig
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- Hochschule für Grafik und Buchkunst Leipzig
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- Bandzählung
- No. 1296, July 6, 1883
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Zeitschrift
The photographic news
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Band
Band 27.1883
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- Titelblatt Titelblatt I
- Register Index III
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Band
Band 27.1883
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- Titel
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418 THE PHOTOGRAPHIC NEWS. LJULY 6, 1883. Only round the poles is it lacking, and here there is a very marked rift. Saturn is shining not far from the sun, and a star or two are pretty plainly visible in the vicinity of the eclipsed luminary. It is a grand spectacle ; but do not imagine that we are wholly absorbed in it. Mr. Fletcher is sticking steadily at his chronometer, and as each ten seconds pass, we hear his voice, and make the necessary changes in the slides. The 300 seconds pass, and he calls out zero. There are yet a few more seconds before the re-appearance of the sun, and Mr. Fletcher gets his first look at the corona. Some of the slides are closed, and others have the plates moved on for another exposure. “Time!" Out comes the sun’s limb, and before many minutes have passed, the last plates in the spectroscopes have received their last exposure. The slides are put in a safe place till the darkness and coolness of the night will permit the latter to be developed with safety. Eye observers write down the things they have seen, while their memories are still fresh ; then, all adjourn to the house to congratulate one another on the opportunities given them. Opportunities indeed, for the clouds had disappeared only a short time before totality, only one light transparent cloud appearing throughout the 325 seconds, and that little obstruction, if it could really be called such, rapidly passing over. Shortly after totality the sky again clouded over, cleared off for an observa tion of fourth contact, and then became obscured for the greater part of the day. And what results were obtained ? Well, to come to particulars first, and mention what is likely to interest your readers most, the photographs obtained were good. The pictures taken in the corona camera were fully equal to those obtained last year with the same instrument. With these, and the pictures obtained with the photo heliograph, we shall be able to get a perfect representation of the coronal detail from the edge of the limb to the extremities of the streamers. The spectrum of the corona was photographed well, and we succeeded in obtaining some of the most prominent lines of the reversion spectrum, or flash, as it has been called, in several instruments. These are our most important photographs. What they tell us, I can best relate in describing the general results of the various expeditions. As your readers are likely to know from observations at home, the sun was not in a very active state. Very few spots were on his disc, and these only of small size. The chromosphere was also very quiet, and the prominences were insignificant. This, coupled with the excess of the moon over the sun in size, rendered some of our instru ments—e.g., the prismatic camera and the Rowland grating —less fruitful in results than we expected them to be. The first of these instruments, which gave a most instructive result last year, gave good photographs on this occasion, but the amount of information to be derived from them is comparatively small. The same inactiveness of the sun seems also to have had its effect on the corona, not so much in general appearance, as in the character of the light emitted. The spectrum was more continuous; though containing many bright lines, these were fewer in number, and of less intensity than in the spectrum photograph obtained in 1882. Ur. Hastings saw the D lines only dark; but M. Janssen asserts that he saw most of the Fraunhofer lines as dark lines. M. Janssen’s observation is most significant, if that gentleman be not mistaken. Unhappily, M. Janssen did not attempt to photograph the coronal spectrum as well. Solar physicists are likely to be treated shortly to a pretty lively discussion on an issue raised by Dr. Hastings. It is the opinion of this gentlema । that the corona—or at least, the outer part of it—is nainly a diffraction phenomenon, and not a true solar appendage, and his observations on Caroline Island tend, he considers, to confirm this view. Giving special attention to the 1474 line, he observed that at the com ¬ mencement of totality it extended to a greater distance on the eastern than on the western limb, and as the moon moved across the sun, the condition of things was reversed; the variations in length, so he alleges, were greater than the moon’s motion could account for. A considerable amount of mathematical work has to be got through before he can publish his report, and until that report is pub lished, I do not care to express any definite opinion. In spite, however, of Dr. Hastings’ undisputed ability, I fear that this case, fully admitting the correctness of his obser vations, is likely to be but a weak one. An exceedingly interesting observation, but one that will require confir mation in the future, is that of Professor Tacchini, who, examining with his spectroscope one of the coronal streamers, saw something resembling a cometary spectrum. This somewhat resembles an observation made by Mr. Lockyer last year, that gentleman noticing well-defined maxima and minima in the brightness of the spectrum, and what looked like flutings. Should this observation of M. Taccbi i's be identical with the previous one of Mr. Lockyer’s, as is not unlikely, it will exert some influence on the hypothesis associated with the latter gentleman’s name. In reference to the work specially done to test Mr. Lockyer’s hypothesis, the photographs taken will re quire a very careful examination before any opinion can be expressed either one way or the other. Before dismissing the spectroscopic work, I must not forget to mention the observations of Mr. Rockwell, who saw several lines in the green not usually seen in the corona. They were probably magnesium. Taking a general glance at the eye observations of the spectrum, they cannot be regarded as too satisfactory, being, in some instances, contradictory. It is becoming more and more evident every day, that where rare and fleeting phenomena are concerned, photography is by far the most reliable observer. But I am forgetting all mention of the planet Vulcan. Still, that is only to be expected, for he altogether failed to put in an appearance when most looked for. Professor Holden, and Messrs. Trouvelot and Palisa, looked for him and found him not, whilst M. Janssen employed a good many photographic eyes, but they have not yet been ex amined. The most definite thing to be said concerning him is Prof. Holden’s statement, that if Vulcan exists at all, bis light is less than that from a star of the 6th magnitude. In conclusion, it may fairly be said that the eclipse of 1883 is not behind any of its predecessors in the fruitful ness of its results, and the time is yet far distant when solar eclipses can cease to be regarded as important. The more thoroughly they are observed, the more intricate do the problems to be solved become. But now this long letter must be closed. In my next communication I will endeavour to give my experiences of photographic work on the island, with other matters of sufficient interest to warrant my placing them before your readers. COLLODION EMULSION AND GELATINE EMULSION. The classic researches of Dr. H. W. Vogel, which have appeared from time to time in our columns, give our readers an excellent opportunity of judging as to the essential difference which exists between the haloid salts of silver in various photographic preparations. In another column will be found an article in which Dr. Vogel treats of the subject anew, and more fully eluci dates those experiments with which our readers are familiar. He points out how essential is the difference between the silver bromide of a collodion emulsion, and the isomeric salt contained in a gelatine emulsion. Both isomers are approximately equal in sensitiveness when a physical developer is used, the well-rccognised greater
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