October 14, 1922" 



NA TURE 



513 



the Serbo-Croatian rules. Czech transcription has 

 the advantage of being complete. 



The following examples may serve to make this 

 clear. Russian a has only one sound, as in " master." 

 It has the same sound in Czech, but the English a 

 has several sounds. If m is rendered by j it is 

 liable to mispronunciation ; if transcribed to the 

 Czech z this liability does not arise. Russian y is 

 always pronounced like the Czech u (like oo in the 

 English word "hook"). Russian x can be correctly 

 rendered by the Czech ch. 



" Hard mute " and " soft mute " (t> and b) can 

 only be transcribed into Czech, using the hook " after 

 the consonant. Russian u has no other European 

 sound except the Czech y. The different pronuncia- 

 tion of the Russian e, -is, n cannot be easily ex- 

 pressed in English, but this becomes easy by using the 

 Czech e for the first two, especially the second. 



It may be pointed out that the Czech transcription 

 is already employed in the International Catalogue 

 of Scientific Literature, and for some years German 

 journals (e.g. Zeitschr. f. anorg. Chem.) have employed 

 letters with diacritical marks in their transcription 

 of Russian names (e.g. " Zemczuznyj," which in Czech 

 is " Zemcuzny "). 



The objection, urged by Lord Gleichen, to the use 

 of diacritical marks exists, but is relatively small. 

 Most scientific journals already have such type, 

 which is indeed necessary if Czech names are to be 

 printed correctly. Newspapers naturally lag behind 

 such a journal as Nature in matters of this kind, 

 but in time these too will doubtless find it neces- 

 sary to have letters with diacritical marks in their 

 founts. 



Lord Gleichen also asks how many English people 

 can correctly pronounce Czech letters like c. It is 

 regrettable, but nevertheless true, that the correct 

 pronunciation of foreign words is not a great char- 

 acteristic of the British people, but it is as easy to 

 learn how to pronounce Czech words as it is those 

 of other languages. The example which was chosen 

 by Lord Gleichen is poor, because the sound " 6 " 

 exactly corresponds to the English sound " ch " 

 (e.g. " church "). 



J. G. F. Druce. 



Bled, Carniola, Jougo-Slavia. 



A. Glazunov 



(formerly docent at 



Petrograd Polytechnic). 



Prague, Krai. Vinohrady, Wenzigova 21, 



Czecho-Slovakia, 



August 5. 



Colour Vision and Syntony. 



In Nature of September 9, p. 357, Prof. E. H. 

 Barton has shown how a syntonic hypothesis of colour 

 vision may be made to represent the trichromatic 

 theory of colour vision. There are numerous facts 

 which are quite inconsistent with any form of the 

 trichromatic theory. These are given in detail in 

 my recent book on the " Physiology of Vision " and 

 subsequent papers, and no attempt has been made 

 to answer any one of them. Every fact points to 

 the visual purple being the visual substance which, 

 sensitising the liquid surrounding the cones, sets up 

 a visual impulse in the cones when decomposed by 

 light. Houstoun's explanation of the physical pro- 

 cesses is in complete accordance with the facts, and 

 so far as I am aware no valid objection to it has 

 been found. 



Any theory of vision must explain the movement 

 of the positive after-image in the retina. For example, 



NO. 2763. VOL. I 10] 



if the positive after-image of a small white triangle on 

 black velvet be obtained with one eye, on moving 

 the head with a jerk, both eyes being covered, an 

 irregular white figure will be seen some little distance 

 away from the clearly cut black triangle, the negative, 

 after-image in the original position which is seen when 

 a small amount of light is allowed to enter the eye- 

 through the lids. Another very simple method of 

 seeing this movement of the positive after-image is to- 

 look at three windows on awaking, which are separated 

 by walls ; on closing and covering the eyes, well defined 

 positive after-images of the windows separated by 

 black spaces corresponding to the walls are seen. 

 On covering the eyes and moving the head from side 

 to side the after-images all blend into one, the black 

 spaces being obliterated. 



Let us compare the model given by Prof. Barton 

 with the known facts of vision. For any particular 

 light the three vibrators acting together should give 

 the luminosity curve for that light. Barton has 

 placed the red vibrator at about X760 up ; here the red 

 has very little luminosity, whereas a driver of the 

 length of the vibrator at this point will produce 

 most effect. Again, drivers corresponding to the 

 infra-red or ultra-violet will affect the red or violet 

 vibrators respectively, whereas these regions are 

 invisible. 



When we come to colour blindness the trichromatic 

 theory fails completely. How on this theory can the 

 fact that more than fifty per cent, of dangerously colour 

 blind people can pass the wool test be explained ? The 

 fact that a dichromic may have a luminosity curve 

 similar to the normal, that the trichromic have only 

 three colour sensations and designate the yellow 

 region as red-green, and the other degrees of colour 

 and light perception, has to be explained. 



F. W. Edridge-Green. 



London, September 19. 



The Green Ray at Sunset and Sunrise. 



The review by Sir Arthur Schuster of Mulder's 

 book on the green ray or green flash at rising and 

 setting of the sun, in Nature of September 16, p. 370, 

 leads me to make the following remarks : 



There are, in reality, two distinct phenomena which 

 go under the name of the green flash. The first, 

 probably the one most usually seen and the only one 

 to which the epithet properly applies, is certainly an 

 after-image in an eye fatigued by the red light of the 

 sun. I have seen it many times, "only at sunset, and in 

 many localities — on the Red Sea (twice in one evening 

 owing to the sun being occluded by a narrow bank of 

 cloud prior to its actual setting), in Devonshire, and 

 even in London as the sun set behind University 

 College Hospital. 



This phenomenon can be reproduced quite easily 

 in the laboratory by means of an artificial red sun, as 

 I demonstrated a few years ago at a meeting of the 

 Physical Society of London. 



The second phenomenon, which I have never been 

 successful in seeing and of which I can say little, is 

 evidently due to atmospheric dispersion ; and, from 

 the published accounts, I should judge that it should 

 be called the blue sun or multicoloured sun or spectrum 

 flash. It would seem to be much more rare, as I 

 gather from Sir Arthur Schuster's previously made 

 descriptions that it requires rather special conditions. 



If this subject should get into elementary text- 

 books, as recommended, at least let the account of 

 it be complete. Alfred W. Porter. 



University College, 

 London. 



Q 2 



