The photographic news

• Bandzählung: 29.1885
• Erscheinungsdatum: 1885
• 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-id1780948042-188500006
• PURL: http://digital.slub-dresden.de/id1780948042-18850000
• OAI: oai:de:slub-dresden:db:id-1780948042-18850000
• Sammlungen: LDP: Historische Bestände der Hochschule für Grafik und Buchkunst Leipzig
• Sammlungen: Fotografie
• Bemerkung: Seite I-II fehlen in der Vorlage. Paginierfehler: Seite 160 als Seite 144 gezählt.
• Strukturtyp: Band

• Digitalisat: SLUB Dresden
• Strukturtyp: Ausgabe

FEBRUARY 27, 1885.] THE PHOTOGRAPHIC NEWS 131 to the audienee, still a photograph of the card showed the painted corona with great distinctness. The other point was in connection with the fact that the coronal light is rich in the violet rays of the spectrum. This light is indeed within the range of the eye, but so near the limit of its power, that the eye is very insensi tive to small differences of illumination. If by some method of selection this light alone is made use of, a great advantage is given to the coronal light, which then can better hold its own against the air glare. Now, in the different behaviour of argentic bromide, iodide, and chloride, we have the means of choosing a film with the needful power of selection, namely, when sensitized with the chloride. Negatives of the sun, taken at the lecturer’s observatory in 1882 and 1883, were shown on the screen, and also copies of some negatives by Mr. Ray Woods made at the Riffel in 1884. MR. COWAN’S ECLIPSING ARRANGEMENT FOR CHANGING LANTERN SLIDES. A lantern picture-carrier, or holder, is made with grooves at top and bottom, in which the slides travel horizontally. When one slide is correctly in position, and it is desired to change it, another is placed ready in a slot cut for the pur pose, and is pushed into the place of the first one by a sliding strip, which can be made to travel horizontally in grooves—this sliding strip, by its’ action, placing the second slide into the position previously occupied by the first; whilst the lantern picture that was just in position is ejected. This sliding strip, in thus placing the slides in position, one after the other, also darkens the screen while the change is taking place. The front end of the sliding strip is bevilled off at an angle of 45° from its lower corner ; and, at the commencement of its action, the point engages under a pin fixed in a rising shutter, and by the time the horizontal shutter has travelled the length of the bevilled part, the vertical shutter has risen and covered the slide which is in the field. 'Ihis shutter may be rigid where room is available, or may take the form of the spring roller blind where porta bility is desirable ; in either case, by the time the hori zontal sliding strip has travelled the width of the pictorial slide, the vertical shutter, or blind, has risen to such a height as to just obscure the picture on the screen. By continuing the action of the horizontal sliding strip, the second slide picture already placed in position for the pur pose is pushed into the place previously occupied by the first. On the horizontal travelling shutter being withdrawn, the vertical slide, or blind, descends, and the second picture is now seen on the screen in place of the previous one. ISOCHROMATIC PHOTOGRAPHY. BY FRED E. IVES. Dr. Vogel, according to his communication in the PHoro- GRAPHIC News of January 1G, appears to think that I claim to have published the first process of isochromatic photo graphy. I made no such claim, and if my article in the Year-Book makes me appear to do so, it is because the printer took the liberty to insert a comma after the word “ photography ” in the first line. What I claimed, and can easily demonstrate, is, that I realized and published the first practically successful method; that that method was a very great step in advance of anything previously pub lished ; and that it was far superior to the process which Dr. Vogel announced more than four years later, and sold as a " secret,” claiming that it was the “ solution of a problem,” &c. Dr. Vogel is reckless when he asserts that he published in 1876 “exactly the same method of preparing isochro matic plates which I published in 1879.” I have already pointed out that the success of my method is due to two things which Dr. Vogel certainly did not publish or even realize—that is, to the use of blue-myrtle chlorophyll, the solution of which is many times more sensitive and power ful for this purpose than any chlorophyll solution which had previously been tried, and to the use of a coloured screen, which anyone could obtain with very little trouble, and the colour and intensity of which could be adjusted to a nicety, and quickly changed to meet the requirements of a different emulsion, or an older solution of chlorophyll, or a subject which would be improved by giving to some particular colour a degree of intensity greater or less than that exactly corresponding to its visual intensity. The mere mention of chlorophyll as a colour sensitizer is of very little consequence, because everything depends upon the nature of the chlorophyll, that extracted from many kinds of leaves having little or no value for this purpose. If I am rightly informed, the chlorophyll em ployed by Becquerel was capable of making the plates sensitive only to a small portion of the red end of the spectrum, and did not perceptibly increase the sensitive ness to orange, yellow, or green. That Dr. Vogel did not know how to obtain a suitable solution of chlorophyll, and did not know what could be accomplished with such a solution, is sufficiently proved by his avowed preference for eosine, which is certainly far less powerful than blue myrtle chlorophyll, and is so insensitive to red that plates prepared with it are very far from being truly orthochro matic. A truly successful process of isochromatic or ortho chromatic photography must, as the name implies, be capable of photographing all colours in the true proportion of their brightness. Measured according to this standard, my method was not only the first, but it is the only suc cessful process of isochromatic or orthochromatic photo graphy with collodion plates. Dr. Vogel not only failed to realize this degree of success at any time, but his earliest method, published in 1873, had so little practical value, thet even he does not appear to have applied it to any useful purpose beyond photographing a ribbon, to prove that yellow could be made to photograph lighter than blue. His own estimate of the practicability of bis early “ pro cess ” ten years after its publication may be inferred from the following quotations from one of his recent publications: “ After an investigation of eleven years, I have succeeded at last [1884] in producing collodion plates which are at least eight times more sensitive to the yellow of the spec trum than to the blue, enabling one to make with the same copy of the table of colours of my instruction book, in which blue, yellow, and rose [not scarlet or ruby-red] are reproduced in natural proportion of tone * * * The Photographic Society passed the resolution to acquire the process and publish it for the benefit of all.” “ It is possible that some may have similar process, but nothing has been published yet, and it has been kept by these people as a secret.” The latter assertion was made more than four years after the full publication of a superior method, in a journal to which Dr. Vogel was a regular contributor at that time. PHOTO-TRICYCLE APPARATUS AS ARRANGED BY MESSRS. CUSSONS & CO. This consists of a portable folding camera with screw focussing arrangement, swing back, and an adapter frame placed in the position of the focus screen, allowing the dark slide to be inserted so as to give the horizontal or vertical position to the dry plate when in the camera. To the front and baseboard a brass swivelled side bar, made collapsible by means of a centre slot, is attached by hinges, and this renders the camera rigid when open, or secure when closed. The base-board is supported on a brass plate, within which is inserted a ball-and-socket (or universal