. Optical projection : a treatise on the use of the lantern in exhibition and scientific demonstration. ed asa transparent slide forthe ordinary stage of the lantern, the cost of the latter arrange-ment with the wheelwork being about 12s. 6d. If now sectors of black paper are fastened, with drawing-pins, on the card disc, or gum on the glass, so as to cover upany of the colours, by so suppressing these again we getcolour. Or we may rotate just in front of the nozzle of the 1 If the colours are not properly painted, of course the white will not beperfect, and a disc should always be tested befo
. Optical projection : a treatise on the use of the lantern in exhibition and scientific demonstration. ed asa transparent slide forthe ordinary stage of the lantern, the cost of the latter arrange-ment with the wheelwork being about 12s. 6d. If now sectors of black paper are fastened, with drawing-pins, on the card disc, or gum on the glass, so as to cover upany of the colours, by so suppressing these again we getcolour. Or we may rotate just in front of the nozzle of the 1 If the colours are not properly painted, of course the white will not beperfect, and a disc should always be tested before purchase, or at least beforeuse. But a beautiful white can be got by this method, and it is the brighterthe more brilliant the colours. It is true the disc often appears a poor greyas usually shown, by the general light of the rooni; since each portion of it canonly reflect at most about one-eighth of the spectrum; hence the grey, whichis merely a deficiency of light. But by keeping the room dark, and concen-trating a bright light on the disc, with a good one the white is all that can LIGHT: COLOUR 289 lantern another card, in which are cut two radial slots as infig. 155, so that the slots cross the nozzle and let flashes oflight through intermittently. Cover the nozzle itself with asimilar slot, taking care of course that the slots come justwhere the rays cross from the objective. Then while theNewtonian disc is rapidly rotated, let the other interceptingdisc also be rotated, at first slowly. The flashes by degrees, astheir speed increases, will not allow all the colours to mingletheir impressions during each, and so the disc will appearcoloured, till at last it will stand out almost distinctly in itsreal colours From all these experiments it will be readily shown and asreadily understood, that for a pure spectrum wemust employ a narrow slit. The narrowest slitgived its own spectrum. That a broad slit givesmany overlapping spectra, is demonstrated by usi
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Keywords: ., bookauthorwrightle, bookcentury1900, bookdecade1900, bookyear1906
