The photographic news

• Bandzählung: 6.1862
• Erscheinungsdatum: 1862
• 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-id1780948042-186200003
• PURL: http://digital.slub-dresden.de/id1780948042-18620000
• OAI: oai:de:slub-dresden:db:id-1780948042-18620000
• Sammlungen: LDP: Historische Bestände der Hochschule für Grafik und Buchkunst Leipzig
• Sammlungen: Fotografie
• Bemerkung: Seite 1-72 fehlen in der Vorlage. Vorlagebedingter Textverlust.
• Strukturtyp: Band

• Digitalisat: SLUB Dresden
• Strukturtyp: Ausgabe

1862. iust met ; to part intende ing ge” istrume nciple d in impot btainis ien, aft a secod action 0 a film’ Wee# resent, * line bail illy gir s a littl he plate ours ptt ical w it I to sens ours of was co; iroto- so -tenth * action ° r in st the fixi®8 3 simple It fort of fisil sr this necessaf until t- place t ed screeH re alreal upon t n, formo <1 direct tt to fo” is left; 1 1, it w ish on J t over t ie come 1 ady to V oduced V t covet" only o!‘ ie porti® hloride I hloride 0 lly ift of heat is fact ’ aving a the ha’ 1, ited pla 11 lours, t mperatul ie varnis) Feb. 28,1862.] THE PHOTOGRAPHIC NEWS. 101 manent. In conclusion:—1st. The chloride of lead applied upon the film of chloride of silver before exposure to the light produces in part the effect of re-heating, that is to say, the white light acts in white upon the lights, and admits of all the hues being obtained much brighter than upon a plate brought only to the rose hue by heat. 2nd. The action of heat after that of light produces upon that portion of the chloride of silver covered with varnish a transient fixing of the heliochromic colours. 3rd. White light bleaches chloride of silver in presence of chlorides of lead, instead of making it turn violet, as it would if it were alone. 4th. The destructive action of light is retarded, it acts more slowly, since it requires ten to twelve hours of diffused light to destroy the colours, which usually takes place in a few minutes, besides, there is not always a relative fixity. 5th. Such is the position of heliochromy at the present day, if the problem of fixing is not actually solved, there are at least reasons to hope for a solution. PROFESSOR TYNDALL’S LECTURES ON LIGHT. LECTURE v.—Jan. 4, 1862. Ins subject of colour blindness formed the subject with which this lecture was commenced. Supposing the audience before him to represent a pretty fair average of London society, the lecturer said that he was perfectly certain that there were then in the room many who did not see all the colours of the spectrum. He knew numbers of people who could not distinguish between a scarlet geranium flower and the green leaves, and it was known that the celebrated Dr. Dalton, of Manchester, could not distinguish between cherries on a tree and the leaves surrounding them. This peculiarity was, strange to say, more prevalent amongst gentleman than ladies. It is in every one’s power to render himself temporarily blind to colour in this way :—take a red wafer on white paper; let it be brightly illuminated by the white light of day; look fixedly at it for minute and then push it suddenly aside. The spot which the wafer formerly occupied will be seen to be green, because the eye being partially deadened to red light, the complimentary colour to the red, present with it in the white light of the paper, makes its appearance. In another way, however, we are all, to a certain degree, blind. There is a spot in each of our eyes where the optic nerve enters the retina, which is quite blind. This may be found out in the following way:—take two wafers, or make two black spots about two and a half inches apart on a sheet of white paper. Then close one eye, the right, for instance, and look with the left perpendicularly down upon the right hand wafer. The image of the left wafer will now go into the eye and fall upon the blind spot of the retina, and the consequence will be that it will be invisible. In this way the image of the full moon can be completely quenched. The subject of chromatic aberration was then briefly described. Taking the case of a simple lens, if a beam of white light be sent through it will be converged or re fracted ; but the violet rays of the beam being more refran gible than the red rays, the former would come to a focus earlier than the latter. The positions of the two foci being different, the distance between the focus of the red and the focus of the violet is called the chromatic aberration. This was illustrated by throwing the rays of the electric light on to a large simple lens. Upon interposing a screen in the path of the rays beyond their focal point there was a disc of light with a blue rim, but upon bringing the screen to a point between the focus and the lens, the disc of light was seen to be surrounded with a red rim, because there the blue cone is surrounded by a red one, the red being least refracted. A brilliant electric spectrum was then projected on to the screen and attention was drawn to the dark space outside the visible spectrum at the red end. No light was visible, although millions of rays were falling on it. These were the heat rays. At the other end of the spectrum also, beyond the violet there are a perfect shower of rays that are invisible to the eye—that might be called too shrill—for as there are notes of sound too shrill to be heard by the human ear, so there are colours too shrill to be seen by the human eye. These were made visible by taking some solution of sulphate of quinine in tartaric acid and moistening a piece of blotting-paper with it. Upon now introducing the blotting-paper into the dark space beyond the violet end of the visible spectrum the part which had been moistened im mediately glowed with a pale blue phosphorescent light. It is this property of sulphate of quinine to render these rays visible that enables these highly refrangible rays which are employed by the photographer, to be seen. This was illustrated in another way. The lecturer interposed a sheet of dark blue glass in the path of the rays, this cutting off the rays of an intensely illuminating power but which have not the property of being rendered visible. Upon then placing the moistened blotting-paper in the blue light, it became quite luminous. The same thing was afterwards performed with the rays from a spark from a powerful induction coil, whereby sulphate of quinine, differ ent kinds of glass, and various powders were rendered fluorescent, as this phenomenon is called. The phenomena of the colour of natural bodies were next considered. That of pure water was shown to be a beautiful green in the following way:—A tin tube, fifteen feet long, with glass ends was arranged horizontally and half filled with water. A sheaf of rays from an electric lamp was then sent through the tube and an image of the end of the tube projected on the screen by means of a lens. The upper half of the bundle of rays of light passed through the air in the which sometimes takes place very suddenly upon those parts directly struck by white light, especially if the chloride of lead be too acid or too concentrated. Under the influence of heat we generally find the colours to become more in tense, especially if the light has influenced the whole thickness of the film of chloride of silver; in the opposite case, the heat causes the blues of the violet and the blacks to turn red ; and this result appears to me very remarkable. It is by this action of heat upon the varnish influenced by light that I obtain the temporary fixing of the heliochromic colours. If we apply the varnish with the base of chloride of lead after obtaining the colours, they brighten; but they last a much shorter time than when the varnish is applied before the colours are obtained, but still their coming is not de layed. Generally all the substances applied in the state of var nish upon the film of chloride of silver, either before or after obtaining the colours, blacken the white portions of the images under the action of light, while all the salts of lead, and especially the chloride, whiten them ; a too concentrated solution of chloride of lead must also be avoided, else too much white chloride will be produced. Many substances, as for example, sulphate and nitrate of copper applied with dextrine upon the film of chloride of silver before exposure to light, cause certain colours to pre dominate and brighten them ; but none fix the colours so long as the salts of lead, especially the chloride. Finally, I hope with this varnish containing chloride of lead, that we may be able almost to entirely suppress the action of re-hcating, whenever the plate has been chloridized either by the electric pile or in an acid bath as indicated above; but with the alkaline bath which I employed in my last experiments, it is still necessary to give a semi-heating to the plate before applying the varnish ; if the plate be brought entirely to the rose hue, the colours are produced more rapidly, the lights are whiter, but the tones are gene rally less vivid; on the other hand the fixing is more per-