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The photographic news
- Bandzählung
- 12.1868
- Erscheinungsdatum
- 1868
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- Englisch
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- F 135
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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. 529, October 23, 1868
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Zeitschrift
The photographic news
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Band
Band 12.1868
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- Titelblatt Titelblatt I
- Kapitel Preface III
- Ausgabe Ausgabe 1
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- Register The Index To Volume XII 619
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Band 12.1868
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8 I Df. innot glish tided e aid It is men n all : the it all nent. were juite ) the able, the Jr, it pher have tion lion, heir tici- ' the ork- the red. lort, ally was i by 1 by lilst edi- igh 3 in the and 3 tO eri- pe- ave on- isk it's the igh 0111 ed. ec- v a the ent it, seo is is- us uld ie- 3 I bit see it- he or it October 23, 1868.] THE PHOTOGRAPHIC NEWS. 509 white. I should, however, say that for long I never saw a Orionis markedly red, nor Antares, and I may not catch red soon, though I cannot conceive this being so. In conclusion, I may note that the darkness was very slight, and the colour not half so gloomy as in the eclipse of 1857, which was partial at Delhi, where I was then. The spectroscopic examination of the eclipse by Lieut. Herschel, given in a letter to Mr. Huggins, will be read with interest by many photographers :— The week preceding the event had quite prepared me for dis appointment. There seems to be an annual cloudy and rainy season at Jamkandi, which lasts about a fortnight, and was said to be somewhat later and more marked than usual this year. The morning broke, however, as usual, clear, but the driving monsoon clouds soon showed the kind of sky we were to expect. About a quarter of a minute before totality a thick cloud obscured the sun. I had placed the slit (of the spectroscope) so as to cross the cres cent at about the vanishing point of the limb, and was watching the narrow solar spectrum grow rapidly narrower. You may con ceive the state of nervous tension at this moment. Whatever the corona was competent to show must in a few seconds have been revealed—unless, indeed, it should so happen that a prominence should be situated at that precise spot, in which case the double spectrum would be presented. But the solar spectrum faded out while it had still appreciable width, and I knew a cloud was the cause. I went to the finder, removed the dark glass, and waited— in that fever of philosophical impatience which recognizes the futility of irritation, even while it chafes under the knowledge of fleeting seconds—how long I cannot say, perhaps half a minute. I can well recall the kind of frenzied temptation to turn screws and look somewhere else, checked by the calm ticking of the clock, telling of a firm hold of the right place, cloud or no cloud. Soon the cloud hurried over, following the moon’s direction, and there fore revealing first the upper limb, with its radiating, and, as I fancied, scintillating corona, and then the lower limb. Instantly I marked a prominence near the needle point in the finder. A rapid turn of the tangent screw covered it with the point of the needle. Those few seconds of unveiling were practically all that I saw of the eclipse as a spectator. With the exception of a hurried fiance into the finder at a later period, to watch for another break, was the whole time engaged at. the spectroscope. I have not the remotest idea, from actual experience, of the external phenomena which were present to the thousands of upturned faces whose voices I heard outside. I might easily have lifted the curtain and looked out while the clouds were obstructing. That I did not do so is only to be explained by the absence of mind, as regarded all else, produced by the concentration of attention on the problem before me. To return: the instant the prominence was under the needle point, I returned to the spectroscope. A single glance solved the problem in great measure. Three vivid lines—red, orange, blue ! No others, no trace of a continuous spectrum. I think I was a little excited about this time, for I shouted, quite unnecessarily, to my recorder, “ Rod, green, yellow I” quite conscious of the fact that I meant orange and blue. 1 lost no time in applying myself to measurement. And here I hesitate ; I have no idea how those five minutes passed so quickly. Clouds were evidently passing con tinually, for the lines were only visible occasionally. The red must nave been less vivid than the orange, for after a short attempt to measure it I passed on to secure the orange, and, succeeding to my satisfaction, tried for the blue line. Here I was less successful. The glimpses of light were rarer and feebler, the line itself growing shorter and further from the cross. I did, how ever, place the cross very near the true position, and got a reading just as the re-illumination of the field of view informed me that the sun had reappeared on the other limb. I consider there can be no question that the orange line was identical withD (sodium), so far, at least, as the instrument is competent to establish an identity. I also consider that the identity of the blue line with F (hydrogen) is not established ; on the contrary, I believe that the former is less refracted than F, but not much. With respect to the red line, I hesitate much in assigning an approximate place. It might have been near C (hydrogen). I doubt its being so far as B, but there would be its limits. The corona may have pro jected a spectrum of some kind, but I saw none. I therefore con clude it was a faint solar spectrum, a conclusion in accordance with other characteristics of the phenomenon, but especially with the (flickering ?) radiating appearance, and with the satisfactory determination by Lieutenant W. M. Campbell, R.E., of the con ditions of polarization obtaining in the corona. At present it is sufficient to state that these observations leave no doubt that the light of the corona is polarized in places passing through the sun’s centre. I have had no communication with any other observers since the event. I am curious to learn how far our results will corroborate each other. • UNEVEN DRYING OF SENSITIZED ALBUMIN IZED PAPER. A DIFFIOULTY, the cause of which is not well understood, but which is productive of most annoying results, is sometimes troublesome to photographers. We refer to the uneven dry ing of the excited albuminized paper. Instead of the solu tion draining and evaporating evenly, a portion of it remains standing in drops, at greater or less intervals, all over the surface of the sheet. These drops dry, of course, very slowly, and in the finished print their places are marked out by grey spots of less vigour than the remainder of the image. Various causes have been assigned for this irregular dry ing, and various remedies suggested, but considerable un certainty as to the actual cause or cure remains. One rea son for its occurrence, suggested by a manufacturer of albu ■ minized paper, is the use of a nitrate bath much stronger than is required by his paper, which, being lightly salted, does not require a strong bath. No reason was stated for the unsatisfactory action of a strong bath; it was simply said that experience had shown that the trouble in question followed the use of a strong bath, and disappeared when a weak one—or, rather, one of the proper strength—was used. The probable explanation of that fact is, that very rapid and very complete coagulation was produced by the strong bath, and the very horny surface had a somewhat repellent action on the solution, causing it to run into drops instead of draining and drying evenly. Another manufacturer of albuminized paper, Herr Schering, of Berlin, sent an inte resting communication to our columns, stating that the defect in question was often the result of the paper having been kept in a very dry place before sensitizing, and that the defect would disappear if the paper were placed in a cellar or damp place for a few hours before it was floated on the silver solution. The only time we met with the trouble ourselves we found this plan proved a remedy ; but we have repeatedly had cases brought under our attention in which neither remedy proved efficient. One simple and certain cure remained, but it was troublesome, and sometimes in troduced another evil. If, instead of allowing the excited sheet to dry in the ordinary way, it was blotted off with clean bibulous paper, there was, of course, no risk of uneven drying. Adopting this course has generally proved quite satisfactory, but in some instances it has been alleged that the prints on such paper possessed less vigour, owing to the removal of the free nitrate by the blotting-paper. A correspondent in India has recently sent us another remedy, which he finds to give eminently satisfactory results in every way. We may mention, by the way, that our receipt of this suggestion affords an interesting illustration of the wide-spread communityof feeling which the devotion to a pursuit of mutual interest engenders. Three months ago, a correspondent, simply signing the initials “J. S.,” in our columns, mentions his difficulty. Another photographer, a major of cavalry in the Punjab, reading his News, and seeing this difficulty mentioned, writes a letter to “ J. S. ” to give him a remedy which he has found to be a perfect cure. The letter is forwarded to us for “ J. S.,” with a suggestion that we should make the recipe public, if we think it worthy. “ J. 8.” and his address are alike unknown to us : a great many of our correspondents in difficulties give us no clue to their identity; nor is it necessary that they should. In case of letters for publication it is, as a rule, necessary that we should receive the name and address of the writers; but we are well content that applicants for advice should preserve their incognito. “ J. 8.” will, however, doubtless see in our columns the letter intended for him, which we now subjoin. “ Rajanpore, Punjab, India, 29th August, 1868. “ Mx dear Sir,—I have just received my Photographic News of the 24th ult, and have noticed that you are in just the same fix as I was, until a short time ago, when a friend helped me out of my difficulty by recommending a dodge
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