The relation of light perception to colour perception / by F.W. Edridge-Green.

  • Edridge-Green, F. W. (Frederick William), 1863-1953.
Date:
1910
Catalogue details

Licence: In copyright

Credit: The relation of light perception to colour perception / by F.W. Edridge-Green. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    Thus it will be seen that if, for instance, the reading on the left drumhead is 5320 and that on the right drumhead is 5950, the region of the spectrum from \ 5320 to \ 5950 is exposed to view in the eye-piece.* The instrument is used as follows:—As far as possible a known quality and intensity of light should be employed. A small oil lamp is quite suitable for the purpose. The observer should first ascertain the exact position of the termination of the red end of the spectrum, the left-hand shutter being moved across until every trace of red just disappears. The position of the pointer on the left-hand drum is noted, and the wave-length recorded. The left drum is then moved so that the shutter is more towards the middle of the spectrum. The right-hand drum is then moved until the pointer indicates the wave-length recorded as the termination of the red end of the spectrum. The observer then moves the left-hand shutter in and out until he obtains the largest portion of red which appears absolutely monochromatic to him, no notice being taken of variations in brightness, but only in hue. The position of the index on the left-hand drum is recorded. The left-hand shutter is then moved more towards the violet end of the spectrum, the right-hand shutter being placed at the position previously occupied by the left-hand shutter. In this way the whole of the spectrum is traversed until the termination of the violet end of the spectrum is finally ascertained with the right-hand shutter. The variation of the size of the patches and the termination of the spectrum with different intensities of light can be noted. The instrument can also be used for ascertaining the exact position and size of the neutral patches in dichromics, the position of greatest luminosity, and the size and extent of pure colours. When it is used to test colour- blindness, the examinee should first be shown some portion of the interior of the spectrum, and then asked to name the various colours which he sees. In this way he will have no clue to the colours which are being shown him. Tested with this instrument a normal individual will, as a rule, name six distinct colours (viz., red, orange, yellow, green, blue, violet), and will mark out by means of the shutters about 18 monochromatic patches. Occasionally we come across individuals with a greater power of differentiating hues, to whom, as to Newton, there is a distinct colour between the blue and violet, which Newton called indigo. Such individuals will mark out a greater number of monochromatic patches, from 22 up to 29. The limited number of monochromatic patches which can be marked out in this way is * This spectrometer has been constructed for me by Adam Hilger, Ltd., and was purchased with a grant made by the Government Grant Cqmmittee of the Royal Society.