General and practical optics / by Lionel Laurance.

  • Laurance, Lionel.
Date:
[1908]
Catalogue details

Licence: In copyright

Credit: General and practical optics / by Lionel Laurance. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

    27/434 (page 11)
    the other two. By stimulating one or more of these nerves, in varying proportions, all the colours of the spectrum can be con- veyed to the brain. These curves are shown in the diagram (Fig- 7). \ f B C I> F Fig. 7. Colours of Light.—A mixture of spectrum red and spectrum green will if mixed in certain proportions produce a sensation of yellow. If spectrum red, green and blue-violet in the right pro- portions be mixed white light is formed. If tho wave-lengths of red and green be added together the mean will give the wave- length of yellow. Thus, taking the wave-length of orange-red as ecpial to G5G and that of blue-green as 518, then G56 + 518 = 1174 and 1174/2 = 587, which corresponds to the wave-length of yellow light. Again, taking the wave-lengths of the three colours red, green, and blue respectively, the sum divided by three will give the wave-length for the Ijrightest part of the yellow, which is the nearest approach to white light which the spectrum affords. Thus, 748 + 527 4- 486 = 17G1 and 1761/3 = 587, which is about the wave-length of the whitest part of the spectrum. The quantity of light of one colour necessary to mix with any other to produce white light, or a third colour, does not appear to follow any law, but the proportions usually remain the same for different observers; occasionally, however, the amount is found to be very different, even among persons who are not colour l)lind to standard tests. Many colours, such as l^rown, ])ink, and purple, do not exist in the spectrum, the latter being a combination of extreme red and extreme violet light. A colour is said to be saturated when pure or not diluted with white. A colour such as brown, is merely orange diluted with white. If three pieces of coloured glass corresponding to the summits of tlie three curves of red, green and blue-violet Ite superimposed, since each absorbs some of the components of white light, the three