800 
NATURE 
[JUNE 16, 1923 

deep-red glass for the shortest possible time the terminal 
red be viewed, it will not be visible. On the trichro- 
matic theory much greater fatigue of the red sensation 
process is obtained with the burning sodium. 
When we come to colour blindness, which, according 
to Helmholtz, is the key of colour vision, the trichromatic 
theory fails completely to explain any case when it is 
fully and thoroughly examined. How, for example, does 
it explain that more than 50 per cent. of the dangerously 
colour blind can get through the wool test ? How are 
the innumerable cases of dichromic vision to be ex- 
plained? All see in the spectrum two simple colours 
and a neutral region, but one is only detected by very 
efficient tests, others by very rough tests: the latter 
are obviously much more colour blind than the first 
class. How are the trichromic, with their absence of 
the yellow sensation and wide monochromatic area 
in the yellow region—for example this may be from 
A6ro pp to A535 pp—to be explained? How is it that 
in so many cases the apex of the luminosity curve 
remains at the normal point and a normal white equa- 
tion is made? Why, indeed, should a man who has 
three colour sensations be colour blind at all? Asa 
matter of fact, there is considerable variation in colour 
perception without colour blindness ; a man may make 
an anomalous white equation without being colour blind. 
Finally, it can be clearly shown that, with a man 
having a defective terminal red, this is not due to a 
-diminution of a hypothetical red sensation which is 
affected by rays corresponding to every part of the 
spectrum. For example, a man may have shortening 
of the red end of the spectrum ; he may pass the wool 
test, or if the proper colours be there, put certain pinks 
and violets together as identical. Shown a bright red 
in the lantern corresponding to the shortened portion, 
he does not see it at all. It will be noticed that the 
pinks he puts with the violets are much lighter than 
the latter, but when viewed through a blue-green glass 
both appear identical in colour and shade to the normal- 
sighted. The blue-green glass has cut off the red rays. 
How, according to Prof. Peddie’s construction, can a 
man with shortening of the red end of the spectrum 
pick out yellow at the normal point and havea luminosity 
curve with the normal apex ? 
The valuable work of Shelford Bidwell, which is so 
inimical to the trichromatic theory, is not mentioned. 
Bidwell showed that the phenomena of intermittent 
light are quite inconsistent with the compound character 
of the yellow sensation. If the image of a white object 
be formed suddenly on a portion of the retina which 
was previously occupied by the image of a black object, 
this image is surrounded by a red border. Bidwell 
states : “‘ Though the image of the needle was colourless 
when the patch was illuminated by the greenish-yellow 
NO. 2798, VOL. 111] 

rays of the spectrum, it appeared red when the same 
hue was formed by combining red and green rays.” 
The fact that the red border is not found with the pure 
greenish-yellow spectral light and is found with the 
compound light is strong evidence against the compound 
nature of the yellow sensation when caused by simple 
yellow light. 
(2) The valuable book by Martin and Gamble should 
be read by all interested in colour. It is very well 
written, and gives an admirable account of the facts 
and views of different writers, without bias towards any 
particular theory. Dr. Martin states in the preface: “It 
is now more than ever necessary that the limitations 
of the trichromatic theory shall be explored, still by 
physically sound methods but by men who are fitted 
to understand the psychological and physiological view 
points. Furthermore, there is a great deal of work 
which needs the most careful verification and checking.” 
The book is divided into three sections. Part one 
deals with the nature of light and colour, colour analysis 
and synthesis, the colours of material objects, their 
nomenclature and measurement, colour in regard to 
illumination, colour in human experience, and colouring 
materials. This part is so clearly written that it can 
be easily understood by any one who has not much 
knowledge of physics and mathematics. Part two deals 
with the eye and its reactions to light, photometry, 
instruments for colour measurement, colour vision with 
an account of the principal theories, and colour blindness. 
Part three is written by Mr. Gamble, and deals with 
colour printing and photography in colours. A number 
of useful tables are given in an appendix. 


Nature Knowledge and Pastime. 
(1) Great and Small Things. By Sir Ray Lankester. 
Pp. xi+246. (London: Methuen and Co., Ltd., 
1923.) 7s. 6d. net. 
(2) The Badger: Afield and Underground. By H. 
Mortimer Batten. Pp. 159+12 plates. (London: 
H. F. and G. Witherby, 1923.) 8s. 6d. net. : 
(3) A Perthshire Naturalist: Charles Macintosh of 
Inver. By H. Coates. With a chapter on Scottish 
Folk-music by H. Wiseman. Pp. xx+244+32 
plates. (London : T. Fisher Unwin, 1923.) 18s. net. 
(4) The Highlands with Rope and Rucksack. By Dr. 
E. A. Baker. Pp. 253+19 plates. (London: 
H. F. and G. Witherby, 1923.) 12s. 6d. net. 
(x) HE volume before us is the fifth, if we are not 
mistaken, in a series of volumes whereby Sir 
Ray Lankester has rendered notable service to those 
persons who, though debarred by circumstance from 
undertaking sustained research, deeply sympathise with 
advance in natural science, are eager for sound informa- 

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