. Scientific news for general readers; a popular illustrated weekly journal of science . late, the natural colours of the variousstripes being as follows :—D R, dark red; L R, light red ;Bl., black ; L, lemon ; Or., orange ; D B, dark blue ; L B,light blue; W, white ; Gr., green; Vio., violet. It will be seen at once that the effects produced on thephotograph are nearly the reverse of those seen in theobject photographed. Fig. 2, on the other hand, shows amuch nearer approximation to right shades, and has beenproduced by using an orthochromatic plate, in the preparationof which erythrosine has
. Scientific news for general readers; a popular illustrated weekly journal of science . late, the natural colours of the variousstripes being as follows :—D R, dark red; L R, light red ;Bl., black ; L, lemon ; Or., orange ; D B, dark blue ; L B,light blue; W, white ; Gr., green; Vio., violet. It will be seen at once that the effects produced on thephotograph are nearly the reverse of those seen in theobject photographed. Fig. 2, on the other hand, shows amuch nearer approximation to right shades, and has beenproduced by using an orthochromatic plate, in the preparationof which erythrosine has been introduced, and by placinga faint yellow glass screen between the object and theplate. It will be noticed that the lemon colour, which appearsdark in Fig. i, is much brighter and more natural in Fig. the orange band the effect is still more striking. Violetwe naturally regard as a moderately dark colour; butphotography has hitherto represented it as one of thelightest. To understand the reason of this let us, for amoment, consider the relation to photography of the three. Fig. 3. great divisions of the spectrum, viz., the chemical, visual,and heat rays. Photography is essentially a chemicalprocess, the chemical and ultra-chemical rays affectingvigorously the sensitive plate. The visual rays have con-siderably less effect; the heat rays have, comparatively,none. If then we place the object shown in our diagramside by side with the spectrum, we can at once see the causeof the reversal of tones in the photograph. The violetband reflects the chemical rays, and the result is a strongimpression upon the plate. Hence a light colour is shownon the finished print. The opposite of this is seen in thecase of the reds, and undoubtedly red is to us a very strikingcolour. Photography, however, requires rays having thenecessary chemical properties, and of these red has little ornone. Practically no effect is produced when the sensitiveplate is exposed to the red rays, and the fin
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Keywords: ., bookcentury1800, bookdecade188, bookpublisherlondon, bookyear1887
