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The photographic news
- Bandzählung
- 24.1880
- Erscheinungsdatum
- 1880
- Sprache
- Englisch
- Signatur
- F 135
- Vorlage
- Hochschule für Grafik und Buchkunst Leipzig
- Digitalisat
- Hochschule für Grafik und Buchkunst Leipzig
- Digitalisat
- SLUB Dresden
- Lizenz-/Rechtehinweis
- Public Domain Mark 1.0
- URN
- urn:nbn:de:bsz:14-db-id1780948042-188000001
- PURL
- http://digital.slub-dresden.de/id1780948042-18800000
- OAI
- oai:de:slub-dresden:db:id-1780948042-18800000
- Sammlungen
- Fotografie
- LDP: Historische Bestände der Hochschule für Grafik und Buchkunst Leipzig
- Bemerkung
- Exemplar unvollständig: Seite 1-82 in der Vorlage nicht vorhanden
- Strukturtyp
- Band
- Parlamentsperiode
- -
- Wahlperiode
- -
- Bandzählung
- No. 1131, May 7, 1880
- Digitalisat
- SLUB Dresden
- Bemerkung
- Paginierfehler: S. XII als S. XX gezählt.
- Strukturtyp
- Ausgabe
- Parlamentsperiode
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- Wahlperiode
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Zeitschrift
The photographic news
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Band
Band 24.1880
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- Register Index 631
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Band
Band 24.1880
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- Titel
- The photographic news
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backgrounds, a warm brown or brownish grey is the tint preferred. The backgrounds are of various kinds; there is and a third description that is hinged, and acts like a practical door. We were shown the properties wherewith all the rustic changes to be seen in Messrs. Hills and Saunders’ cabinet pictures are carried out. Hay, dried grasses, dead palm leaves, together with a few growing plants in pots, and some branches and twigs, comprised the whole. “ We throw nothing away,” said our host, taking up a brown palm leaf from the floor ; “ we only take care to change the arrange ment with every picture.” We have scarcely time to speak of the laboratory and dark rooms. Gelatine plates are in constant requisition at Porchester Terrace, but so are wet plates. The ordinary dipping bath is not to be seen at all here ; the sensitizing baths are of a horizontal character, swinging on pivots, of the same nature as those we described at the Autotype Com- panj’s works. The interior is of paraffined wood, and they possess the advantage that less silver solution is needed, while the plates are permitted to drain more effectually. “One guinea for the sitting, which must in all cases be paid at the time,” is a notice we extract from the card of Messrs. Hills and Saunders, and for this guinea the sitter may take his choice of twelve cartes-de-visite, twelve vignettes, twelves medallions, six cabinets, or four boudoir pictures. Proofs are generally sent out the same evening, but always in an untoned and unmounted condition. The next “At Home” will be “ The Kew Observatory.” THE EYE AS AN AUTOMATIC PHOTOMETER. At the last meeting of the Physical Society a paper was read by Mr. William Ackroyd on the human eye as an automatic photometer. According to Mr. Ackroyd’s experiments the eye itself is a fairly good light measurer. When a “ spot ” or star of light is looked at from a distance, it is seen to omit “ rays ” or spokes of light at all angles. These are due to the radiate structure of the crystalline lens and to the lachrymal fluid on the surface of the corner of the eye. The rays are of various lengths, and are shorter in the 1st and 2nd quadrants, next the nose, near the blind spots, than on the 3rd and 4th quadrants—a fact probably due to the insensi bility of this region. The iris expands and contracts under the stimulus of light independently of the will; and both irises act sympathetically. Now the iris lies between the seats of irregular refraction, and thus any change in the size of the pupillary aperture will be rendered evident by an alteration in the length of the longer rays of a spot or point of light. On this fact is based the use of the eye as an automatic photometer. The sensitiveness of the iris varies in different persons. Mr. Ackroyd found that a sperm candle, burning 120 grains per hour, produced a distinct movement of his iris when 14 yards distant. In employing the eye as a photometer, he adopted the principle that if the light from one source A falling on the eye is capable of producing movement of the iris at a distance d, and the light from a different source B is capable of producing the same movement at the distance d, then the relative intensity is proportional to the squares of these distances. To carry this out in practice the observer is in the dark, and an artificial star is placed on a level with the eyes at a fixed distance. Below this is placed the light to be tested in the same plane. While gazing steadily at the star the other light is to be eclipsed and revealed, and the observer is to find a position whore the revealing of the second light does not influence his iris, as shown by no apparent shortening of the rays of the star taking place. He then approaches gradually till a second position is reached, when the revealing of the second light does produce a movement of the iris. The distance between his eye and the light d is measured. A third light is now put in place of the second, and the same observations repeated, so as to get a second distance d. From these distances the relative intensities are calculated. Owing to the sympathy between the two irises these experiments were binocular. This sympathy may prove convenient in constructing an eye-photometer, since one eye can be turned to the light to be estimated while the other is looking at the artificial star. This method of photo metry would be too delicate for comparing powerful electric lights, unless aided by mechanical means. SEEING BY ELECTRIOITY. BY JOHN PERRY AND W. B. AYRTON. Wb hear that a sealed account of an invention for seeing by telegraphy has been deposited by the inventor of the telephone. Whilst we are still quite in ignorance of the nature of this invention, it may be well to intimate that complete means for seeing by telegraphy have been known for some time by scientific men. The following plan has often been discussed by us with our friends, and, no doubt, has suggested itself to others acquainted with the physical discoveries of the last four years. It has not been carried out because of its elaborate nature, and on account of its expensive character, nor should we recommend its being carried out in this form. But if the new American invention, to which reference has been made, should turn out to be some plan of this kind, then this letter may do good in preventing monopoly in an invention which really is the joint property of Willoughby Smith, Sabine, and other scientific men, rather than of a particular man who has had sufficient money and leisure to carry out the idea. The plan, which was suggested to us some three years ago, more immediately by a picture in Punch, and governed by Willoughby Smith’s experiments, was this:—Our trans mitter at A consisted of a large surface made up of very small separate squares of selenium. One end of each piece was connected by an insulated wire with the distant place, B, and the other end of each piece connected with the ground, in accordance with the plan commonly employed with telegraph instruments. The object whose image was to be sent by telegraph was illuminated very strongly, and, by meansofa lens, a very large image thrown on the surface of the transmitter. Now it is well known that if each little piece of selenium forms part of a circuit in which there is a
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