The detection of colour-blindness from a practical point of view / by F. W. Edridge-Green.

  • Edridge-Green, F. W. (Frederick William), 1863-1953.
Date:
1889
Catalogue details

Licence: Public Domain Mark

Credit: The detection of colour-blindness from a practical point of view / by F. W. Edridge-Green. Source: Wellcome Collection.

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

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    of colour-blindness vary in so many particulars that considerable experience will be required before an ex- aminer is competent to pass or reject candidates for the marine or railway services. The nature of the test has nothing to do with this, the facts are there and only require to be detected. It is as useless to set an inexperienced person to test for colour-bhndness as it is to ask a student who has only a rudimentary knowledge of the use of the ophthahnoscope to diagnose some retinal affection from a description in a book. It must be remembered that a colour-bhnd person has never seen colours as the normal-sighted see them, and therefore is not acquainted with the nature of his defect. We have equally to test stupid as well as very shrewd persons. A few words on my theory of colour-perception will be necessary for a proper appreciation of the following tests. It is a theory essentially based on the perception of differences in a physical series. A normal-sighted person can see six distinct colours in the spectrum, that IS to say, six points at each of which there is a distinct difference. Then as each of the colours at these points must, by the connection of other points, pass gradually mto each other, we have modifications of each of these colom-s or units. An absolute psycho-physical colour unit is a portion of the spectrum which appears mono- chromatic. The approximate psycho-physical colour imits are the number of distinct colours seen, and these are the most important, and are the only ones which it is necessary to pay attention to, because if the absolute psycho-physical units increase in size, it follows as a matter of course that the approximate psycho-physical umts must diminish in number, the length of the spectrum remaining the same. The spectrum may also be shortened at either the red or the violet end, but this may occur without diminution in the number of units and vice versa. ' This theory is supported in every particular by the exammation of 101 cases of colour-bhndness. The fol- lowmg tests are based on the facts obtained from these exammations. The colour-blind may, therefore, be divided into two