TRANSACTIONS OF SECTION I. 653 
comparison by the observers, but also by an examination of the criteria by 
which the objectivity of an impression is determined: the most important 
of these are the steadiness, clearness, and spatial form of the impression, 
and its relation to subjective activity. An impression which fluctuates or appears 
only momentarily is likely to be ignored or regarded as purely subjective, and 
it is in this respect that the uniocular images evoked in these experiments differ 
most from the binocular. 
8. Colour-perimetry in the Dark Adapted Eye. 
By Professor Francis Gorcn, F.R.S. 
9. A Criticism of the Report of the Departmental Committee on Sight 
Tests. By F. W. Epriwce-Green, M.D., F.R.C.S. 
This committee was appointed ‘To inquire what degree of colour-blindness 
or defective form-vision in persons holding responsible positions at sea causes 
them to be incompetent to discharge their duties; and to advise whether any, 
and if so what, alterations are desirable in the Board of Trade sight tests at 
present in force for persons serving or intending to serve in the merchant 
service or in fishing vessels, or in the way in which those tests are applied.’ 
I propose in this criticism to confine myself to the first part of the reference, 
namely, that dealing with colour-blindness. 
The committee recommend that the wool test be retained, but further modi- 
fications be made of it. They suggest that the skeins be divided into groups 
and a dark brown skein be added. The necessity of dealing with the whole 
of the skeins in doubtful cases was first pointed out by me over twenty years 
ago. The committee have missed the most important points in the use of any 
test in which wools are employed. The first is that the test should contain the 
confusion-colours of the colour-blind. The second that the four chief colour 
names, red, green, yellow, and blue, should be used. If the test do not contain 
these essentials normal-sighted persons will be rejected and colour-blind persons 
passed. This I have demonstrated repeatedly. It is evident that the com- 
mittee have not recognised how very defective a man may be and yet pass the 
official test of the Board of Trade with the ease and rapidity of a normal- 
sighted person. In the ‘ Lancet’ of June 22nd I have given an example of a very 
dangerous case of colour-blindness which I examined for the first time in the 
presence of Professors F. T. Trouton and A. W. Porter. Examined with the 
official test of the Board of Trade the examinee picked out and matched all 
five test-colours, green, rose, red, purple, and orange-yellow, easily and cor- 
rectly; he did not touch a confusion-colour. Examined with the largest aper- 
ture of my lantern, measuring { of an inch in diameter, at a distance of 20 feet 
he called red A, nothing and green; yellow, red; red B, white; neutral, green; 
and green, white and red. 
The committee have recommended a lantern of their own construction. It 
is absolutely necessary to have means of regulating the luminosity of the light. 
In the lantern suggested by the committee this cannot be done, and many 
colour-blind persons would learn the sequence and appearance of the colours, 
and with a little practice would tell all the colours on the method suggested by 
the committee. There are many other essential details which have not been 
considered, as, for instance, the exact spectroscopic composition of the colours. 
It will be seen from the report that the possibility of dispensing with it and 
going back to the wool test is mentioned. In fact, with the lantern suggested 
it is quite possible that this might come about, 
The committee have recommended a classification of colour-blindness based on 
the flicker method of photometry. The classification is based on two assump- 
tions: first, that colour-blind persons can be classified by measuring the 
luminosity of their colour sensations; secondly, that it is possible to do this 
by the flicker method of photometry. There is the strongest evidence that 
neither assumption is justifiable. The classification is in direct opposition to 
the work of the ablest observers. 
