Airships past and present, together with chapters on the use of balloons in connection with meteorology, photography and the carrier pigeon . s not appear to correspond to any particular colourof the spectrum, but to be made up of a number of components,each with its own peculiar physiological effect, the photographicreproduction will show a totally different grading. The brightyellow will still appear darker than it ought to be, and the darkblue will produce somewhat of the effect of white. This effect is exaggerated in balloon photography. The blue 300 AIRSHIPS PAST AND PRESENT. rays are mor
Airships past and present, together with chapters on the use of balloons in connection with meteorology, photography and the carrier pigeon . s not appear to correspond to any particular colourof the spectrum, but to be made up of a number of components,each with its own peculiar physiological effect, the photographicreproduction will show a totally different grading. The brightyellow will still appear darker than it ought to be, and the darkblue will produce somewhat of the effect of white. This effect is exaggerated in balloon photography. The blue 300 AIRSHIPS PAST AND PRESENT. rays are more largely absorbed by the air than the others, andtherefore all bright objects appear redder and consequentlydarker on the plate. An effect of absorption and reflection isthat all the bright colours are, as it were, displaced towards thered end of the spectrum and the darker colours appear is therefore necessary to supplement the effect of the brighterlight, which is partially deflected or absorbed by the aqueousvapour and atmospheric dust, by using yellow filters. On theother hand, the chemical effect of the blue rays must be. Fig. 187.—Photograph of a village, taken at night, by means oE an electricprojector, by the Vega Company of Geneva. restrained in order that they may appear darker on the filters can therefore be used in a good light, because thetime of exposure in a balloon can generally be reduced. Probablythe best filters are made by inserting a sheet of coloured gelatinebetween two sheets of glass with optically true surfaces, or asheet of gelatine can even be used alone. The filters should beused with suitable plates, which are so prepared as to have atendency to emphasise the red values. For instance, plates canbe obtained which give a brighter value to yellow than to blue,but any given plate has a tendency to emphasise some particularcolour. In any case, such plates give a better result than theordinary kind. The Perxanto plates, prepared a
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Keywords: ., bookcentury1900, bookdecade1900, bookpubl, booksubjectaeronautics
