438 SECTIONAL TRANSACTIONS.—J. 
of prose wherein a biological hypothesis was made clear by a simple chemical 
analogy. 
Two minutes were allowed for the study of each task and an immediate 
recall was asked for two minutes after the study of the last task. After a 
week’s interval a further recall was made. The possible score for each 
task was ten, a mark for each correct clue or solution and for each essential 
point in the prose passage. 
AFTERNOON. 
Mr. C. A. CLaremMonT.— The psychology of proof (2.0). 
How do we apprehend the causal relation? Is it (1) by habit; (2) by 
some kind of innate pre-disposition of the mind to arrange and regard its 
content in that manner, or (3) is it by a process of direct perception not at 
all resoluble into terms of sensation, memory and so forth ? 
Recent work (Kohler, McDougal, Montessori, etc.) leads one to suppose 
that the latter view is correct. ‘The same work indicates that the power 
which operates is limited ; that is to say, it is possible to ‘ perceive direct ’ 
certain forms of causal relation, but not others ; and this limitation varies 
in scope not only from individual to individual but from species to species. 
Examples are given to show the limitation in man’s case, together with the 
need for an extended notion of causality to include static causal relations 
and also abstract relations of necessity. ‘The latter may or may not involve 
movement (which introduces a time factor) without altering the funda- 
mental fact that they are causal 77 se. 
If we can accept this direct perception and its limitation, it gives the key 
to the psychology of proof ; since proof is only necessary for those causal 
relations which we cannot see direct, and proof can be shown to consist in 
all cases of a reduction of such causal relation to an assembly of those which 
we can see direct. ‘The logical syllogism is itself a direct perception of 
this kind. 
Because the human mind has a range sufficiently great to include not only 
a variety of causal relations, but also the syllogism, it is possible for man to 
creep outside the limited circle of his own ‘ direct perceptions,’ in a way 
that no animal could do. Thereafter he can proceed indefinitely but he 
must go one step at a time. 
Dr. M. CoLiins.—A comparison of tests of colour-blindness (2.45). 
Candidates for entrance into the printing industry in Edinburgh are 
given, as part of their psychological examination, tests of colour discrimina- 
tion. Any boy suspected of being colour-blind is given extra tests to con- 
firm or otherwise the diagnosis. It was thought it would be of interest to 
compare a number of tests of colour-blindness, by giving them not only to 
colour-blind individuals, but also to individuals with normal colour vision. 
Accordingly, all boys, coming up for vocational testing during the past year, 
were given a series of colour-blind tests. ‘The same group of tests was also 
given to a number of colour-blinds. ‘This has resulted in the tests being 
given to 121 boys with ‘ normal ’ colour vision and to twenty boys who are 
red-green colour-blind. An estimate of the validity of each test is therefore 
possible from the practical point of view. 
Dr. F. W. EpripGe-GreEEN, C.B.E—The principles of a test for colour- 
blindness (3.30). 
(1) It should be able to detect colour-blind persons. 
(2) It should show quite clearly who is, or who is not, dangerous when 
