Airships past and present, together with chapters on the use of balloons in connection with meteorology, photography and the carrier pigeon . -ness of the atmosphere, and this must be taken into account. Boulade has drawn up some figures which may help as aguide towards estimating the time of exposure, and take intoaccount a number of variables. Co-efficients for- Aperture. Time of year. Height of the condition of the Sky. 1Sun. J 30 F ltj F S June. July, August = 10April. May = 1-5March, September = 2-oFebruary. October = 30January, November = 4-0Decvmber Zenith = 150° =265° W. = 665° E. = 3
Airships past and present, together with chapters on the use of balloons in connection with meteorology, photography and the carrier pigeon . -ness of the atmosphere, and this must be taken into account. Boulade has drawn up some figures which may help as aguide towards estimating the time of exposure, and take intoaccount a number of variables. Co-efficients for- Aperture. Time of year. Height of the condition of the Sky. 1Sun. J 30 F ltj F S June. July, August = 10April. May = 1-5March, September = 2-oFebruary. October = 30January, November = 4-0Decvmber Zenith = 150° =265° W. = 665° E. = 3 blue =1 L6slightly cloudy : 1 5half covered = 2overcast — 3heavy clouds = 6 4 1 298 AIBSHIPS PAST ANP PBESENT, Colour values must also be considered. The eve sees no suchdifferences between light and shade in a balloon as are noticed on the earth. The shadows seem to be so strongly lighted thatin the distance they almost entirely disappear. The ordinaryphotograph takes no account of colour as such: the variouscolours are only distinguished from one another by patches ofgreater or less intensity. Light and shade are reproduced, but. Fig, 185.—Clouds over the Alps.(Photograph \ S] a monochromatic reproduction of a colour effect grades onecolour into the next by a mere or less abrupt change from lightto dark. Nobody can say exactly how dark a certain patchought to be in order to give effect to the colour of an object, andthis depends on the fact that the effect of a colour on the eye isby no means the same thing as the chemical effect of the colouron the sensitive emulsion. It we consider the Suns spectrum those colours appear to usto be the brightest which are nearest the red end of the scale. BALLOON PHOTOGRAPHY. 299 Red and yellow seem bright; green, blue and violet seem muchduller. But on a photographic plate the reverse is the blue and violet rays have the greatest actinic effect, thered ones have the least. Consequently the print shows blue aswhite and red as
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Keywords: ., bookcentury1900, bookdecade1900, bookpubl, booksubjectaeronautics
