178 



NATURE 



[October 6, 192 1 



high in the scale) are born helpless, and must develop 

 mentally and physically in response to use before they 

 can reach maturity and power of maintaining inde- 

 pendent existence. 



Dr. Bather writes with an air of surprise, "Actually 

 we are now talking of biological method." But have 

 we talked of anything else? What other is the insist- 

 ence on precision of language and the necessity for 

 crucial testing, and the discussion about the nature of 

 evidence and proof? He continues, "My own diffi- 

 culty has been to devise a question that should be uni- 

 versally accepted as crucial, or, having devised one, to 

 elicit the relevant facts." He indicates the trouble 

 exactly. Many biologists — among whom I am sure 

 must be Dr. Bather himself — have tested their sup- 

 positions thoroughly and established them completely, 

 and yet have had them rejected on irrelevant grounds 

 by large sections of their fellows who have unlike 

 ideas as to what constitutes evidence and what proof — 

 Darwin with his theory of natural selection, for 

 example. Some years ago the late Prof. William 

 James, much amused, furnished me with a case in 

 point. He had happened on an article which seemed 

 to him, as it afterwards did to me, good and conclusive. 

 This he submitted to a biological colleague, who, while 

 disputing not a fact (the facts were indisputable) or an 

 inference (I think the inferences were incontrovertible), 

 quite simply declared that he hoped they had done 

 with that sort of thing for ever. It seems he was a 

 devotee of one of the exact and modern methods. 



As to the "difficulty ... to elicit the relevant 

 facts," I, of course, know nothing about Dr. Bather's 

 special troubles ; but I do know that biologists in 

 general have always extraordinarily restricted the area 

 in which they have sought their facts, and that, in 

 the search for exactitude and modernity, they have 

 recently restricted it still further. Of course, other 

 things being equal, "biologists who can experiment 

 with their material are certainly in a far better position 

 to perform both these operations than one who can 

 only observe portions of extinct animals." But that 

 is not the point in dispute. Many sciences deal with 

 organisms that are not extinct ; and while experiment 

 may add, and, indeed, has greatly added, to our know- 

 ledge, it can do no more ; for, after all, it is only one 

 out of several ways of collecting evidence. Dr. Bather 

 says : "Either the glaring truism is an identical pro- 

 position or it is a statement actually disputed." I 

 believe he is not quite correct. The statement that 

 "variation is the sole cause of non-inheritance" is, 

 in effect, identical with the statement that, " apart 

 from variations, like exactly begets like w'hen parent 

 and offspring develop under like conditions," and it 

 is actually disputed. Moreover, the truism is prac- 

 tically identical with the statement that, "apart from 

 variations, offspring tend to recapitulate the parental 

 development." It is true that biologists are divided 

 on this point — as they are divided on almost every- 

 thing else — but only, ' I think, because they use the 

 words "inherit" and "reproduce" as synonymous. 

 I hope to deal with this matter shortly. 



I assure Dr. Kidd (Nature, September i, p. ii) 

 that there is no "catch" in this correspondence. I 

 have used the plainest and simplest language I can 

 think of, and have pleaded only for the use of ordinary 

 scientific methods, including 'plain and precise lan- 

 guage. I am too ignorant to reason about the hair- 

 patterns of the modern horse ; but of this I am sure, 

 that if the collar altered the hair-pattern of the ancestral 

 domestic horse, and if the modern colt reproduces this 

 alteration without experience of the collar, then we 

 have here not inheritance, but variation of a very 

 remarkable and unusual sort. In that case the modern 

 horse is like his domestic ancestor neither by nature 

 nor by nurture. He is like only in very superficial 

 NO. 2710, VOL. 108] 



seeming. If Dr. Kidd will not accept the blacksmith's 

 arm as a good illustration, why not reason from that 

 of the ordinary man, which also, as I say, develops 

 in response to functional activity, and has so developed 

 not for twenty, but for twenty thousands of genera- 

 tions. G. Archdall Reid. 

 Southsea, September 6. 



The Green Colouring of Surf on the Horizon. 



On December i6, 1920, at sh. 30m. p.m. Central 

 Java time, while the steamer van Noort was passing 

 by the small island of Pisang, north of Kroe, on the 

 western coast of Sumatra, at a distance of about 

 3 km., I noticed that the breakers on the shore were 

 not white, but green. Observing the phenomenon 

 with a binocular it was possible to see more details. 

 The low breakers especially showed the green colour. 

 Breakers rising higher became white, the lower right 

 and left corners, however, remaining green. As the 

 breaker ran forward along the shore a green corner 

 preceded, and sometimes the separate crests seemed to 

 be coloured. Along the shore of Sumatra, at a dis- 

 tance of 7 km., no particular colours could be ob- 

 served. From the upper decks of the steamer the 

 colour could be seen, but it was less intense. 



The weather w-as calm, the sky partly clouded, and 

 the sea grey. The horizon was strongly dipped; I 

 saw a sharp horizon before the isle, the surf seeming 

 to rise above this horizon. By no means could a con- 

 tinuous surface of the sea be seen between the ship 

 and the island. The phenomenon disappeared at 

 6h. lom. p.m., when the yellow shore-line of the isle 

 had become invisible below this apparent horizon. 



My object in directing the attention of readers of 

 Nature to this phenomenon is to learn whether the 

 green colouring of surf has ever been observed 

 before. I have been unable to find any description of 

 it, and shall be very glad to learn whether the pheno- 

 menon has been seen and recorded by others. 



As to the explanation, I believe the cause to be the 

 same as that of the "green flash," as the phenomena 

 agree remarkablv in some respects. 



Observations of the green flash have been published 

 in Nature (vols. 93, 94, and 95 of 1914-15). Mr. C T. 

 Whitmell writes :— " Under favourable conditions at 

 sunset, as the upper segment of a yellow sun gradually 

 diminishes, the right and left corners of the segment 

 become green ; this colour gradually spreads inwards, 

 becoming marine, until finally the last tip of the sun 

 may appear almost greenish-blue " (Nature, March n, 



19 15, vol. 95, p. 35)- . , ,_ J u T\ n 



The same observation has been made by Dr. C. 

 Braak (" Hemel en Dampkring," August, 1915, p. 52;. 

 Both phenomena seem to be caused simply by atmo- 

 spheric dispersion of light, as is explained, for 

 example, in a most valuable article by Dr. A. A. Kam- 

 baut ("The Green Flash on the Horizon," Symons s 

 Meteorological Magazine, No. 41, 1906). 



The green flash and the " green surf " are not very 

 common phenomena. Dispersion being always pre- 

 sent, one mav wonder w^hv the green colouring is 

 rather rare. Evershed discussing this fact writes :— 

 " It seems to me verv probable that this phenomenon 

 is in some wav connected with the abnormal condi- 

 tions which at 'sea produce mirage effects. The layer 

 of dense air in contact with the sea might produce 

 total reflection for solar rays refracted from below the 

 horizon, but the critical angle of reflection will depend 

 on wave-length, and it is possible under certain condi- 

 tions that the green ravs mav be totally reflected, 

 whilst the red are refracted " (Nature, May 15, 1915. 

 vol. 95, p. 286). 



