I^eh. 24, 1887] 



NATURE 



391 



reasons can be : T only know that they must be of a totally 

 (liferent order from those which constituted the substance of his 

 published criticism. 



Of course the question whether or not these physiological 

 varieties Jo occur is quite distinct ; and I most heartily agree 

 with Mr. Wallace that this is a question of fact which ought to 

 be decided, before it can be worth anybody's while to attack my 

 suggestion upon any other grounds. If Mr. Wallace had seen 

 this in the first instance, he might have saved both himself and 

 me a good deal of trouble ; but at the same time he would have 

 deprived me of no small axount of encouragement. For I am 

 now more than ever satisfied that the suggestion does not admit 

 of being assailed on any grounds of general reasoning; but, 

 on the contrar)', that as a theory it is antecedently probable, 

 and can only be refuted— if it is to be refuted— by an appeal to 

 fact in the form of e.xperiment. And as I cordially hope that this 

 may be the last time that I shall have to address you upon this 

 subject, I should like to neutralise the discouraging influence on 

 experimental verification which may have been exercised by 

 premature criticism in your pages. This I hope in some measure 

 to eflect by making two remarks. The first is that my own 

 estimate of the antecedent probability of the theory is shared 

 by some of the highest "authorities" on the Continent. The 

 second is that, in all the lines of inquiry hitherto pursued, I find 

 striking evidence of the actual occurrence of the physiological 

 varieties in question. But as this evidence requires to be largely 

 supplemented by experiment, and as every experiment requires 

 at least three years to perform, those biologists who think with 

 Mr. Wallace may be glad to hear that it will be a very long 

 time before I shall have occasion again to trouble them with 

 the theory of physiological selection. 



George J. Romanes 



The Alleged Ancient Red Colour of Sirius 

 With reference to your paragraph last week (p. 378), in the 

 " Astronomical Column," on "The Alleged Ancient Red Colour 

 of Sirius," it does not seem to have been noticed that the early 

 obsen'alions of Sirius were made at its heliacal rising. Under 

 these circumstances the sun is a red star. F. R.S. 



A Green Light at Sunset 



.\T sunset to-night I observed a phenomenon which has, I 

 l.elieve, been seen from on board ship, but never probably from 

 a place with such a distant sea horizon as we have here — some 

 seventy miles. The sky for a short distance above the point 

 where the sun set was perfectly clear of cloud or haze, and I 

 watched carefully the last portion of its disk disappear into the 

 sea. .\s soon as the last speck of the yellow vanished, a 

 momentary bright green flash shone out. This was quite 

 different from the complementary green seen after looking at the 

 setting sun ; brighter and bluer in tint. I have seen it stated 

 th.it the cause of this green light is the sun shining through the 

 water that hides it, and would be glad to know if such is the 

 true explanation. R. T. O.MOND 



Ben Nevis Observatory, February 12 



Sunset Phenomenon 



On February 21, at 5.25 local time, my attention was 

 attracted by a bright red glow reflected from the earth out- 

 side a window having an eastern aspect. 



On going out of doors to the Observatory, it was evident that 

 this crimson light proceeded from a band of cloud about 10° in 

 width forming a great circle in the heavens, and intersecting the 

 horizon at points, as well as I could estimate, 145° W. and 

 35^ E. of true north, the inclination of this great circle to the 

 horizon being about 15° or to". 



In less than three minutes, before I could reach the Observa- 

 tory, the magnificent spectacle had completely vanished, and in 

 the place that it h.ad occupied were merely some streaks of 

 cirrus and cirro-stratus, the latter being nearest to the place 

 where the sun had set, and in half an hour the entire heavens 

 were cloudless. 



Will reflection, or refraction, or both, suffice to explain the 

 above? We.ntwortii Erck 



Sh,inkhill, Co. Dublin 



Aspects of Clouds 



I.N Mr. Raskin's "Modern -Painters" (i. P.irt 2) I have 

 noticed the following passage amongst the author's remarks on 

 the aspects of clouds : — 



" I have often seen the white, thin, morning cloud edged with 

 the seven colours of the prism. I am not aware of the cause of 

 this phenomenon ; for it takes pl.ace not when we stand with our 

 back^ lo the sun, but in clouds near the sun itself ; irregularly 

 and over indefinite spaces, sometimes taking place in the body of 

 the cloud. The colours are distinct and vivid, but have a kind 

 of metallic lustre upon them." 



And .igain, the author describes the "scattered mists rallying 

 in the ravines and floating up towards you along the winding 

 valleys till they couch in quiet masses, ;>/i/rtr<;»Avith the morning 

 light, upon the broad breasts of the higher hills." 



Dr. Johnstone Stoney recently read a paper to the Royal 

 Dublin .Society entitled " The Iridescent Phenomena in Clouds,'' 

 wherein he explains the cause of a somewhat similar appear- 

 ance which clouds at times present. Their outer portions 

 are suff'used with soft shades of colour like those of mother-of- 

 pearl, a lovely green being generally conspicuous. The tints 

 are usually distributed in irregular patches as in mother-of-pearl, 

 but in some cases they form a regular fringe. Dr. Stoney 

 explained that these phenomena are due to particles of ice, in 

 the form of crystals of various sizes and shapes, and according 

 to their position and character the sun's rays are reflected 

 through them in various colours, thus producing the beautiful 

 e ffect. 



Would this be an explanation of the appearances to which 

 Mr. Ruskin refers? Robert J.^mes Reilly 



Boyle, Ireland, February 17 



A Recently-Discovered Deposit of Celestine 



It may, perhaps, be worth mentioning that a large and 

 valuable layer of celestine has been lately found at Vate, in 

 Gloucestershire. It lies just below the sub-soil upon a bed of 

 red Triassic marl, which rests unconformably upon the coal- 

 measures, just at the eastern edge of the Bristol coal-field in 

 that district. 



The deposit is, for the most part, about half a metre or more 

 in thickness, and consihts chiefly of loose nodules which, when 

 broken, are seen to be masses of white, crystalline, nearly pure 

 celestine. Geodes are occasionally found, one of which, about 

 IS cm. in diameter, lined with fine clear crystals, is now in our 

 school museum. Beautifully transparent, though not well crys- 

 tallised masses of selenite also occur in the deposit, and in these 

 are sometimes inclosed single detached crystals of celestine. I 

 picked out one crystal (though it seemed almost sacrilege to 

 break up the fine specimen of selenite), which is about 7 x 4'5 

 X I'S cm., doubly terminated, fairly clear, and showing very 

 perfect, well-developed faces. Its density is 3-95, and it shows 

 very perfectly the characteristic light-blui.sh tinge of celestine. 



It would, I think, be quite worth while for any mineralogist 

 who happens to pass near Bristol to pay a visit to the place, 

 which is only about twelve miles distant on the Midland Rail- 

 way to Gloucester. The extent of the deposit is not known, 

 but when I was there in October last, and again at Christmas, 

 it was being worked in several fields north-east of the church, 

 about a mile and a half from the i-tation. Large quantities are 

 being sent away, of course for the purposes of sugar-refining and 

 adulterating white-lead paint. H. G. Madan 



Eton College, February 21 



"Culminating Sauropsida " 

 It is with satisfaction that I note in Nature of February 3 

 (p. 331 . that Prof. W. K. Parker finds it more and more im- 

 possible "to conceive of birds as arising direct from the Dino- 

 saurians. or indeed from any other order or group of reptiles." 

 The sentence, no doubt, suggests an indirect origin of birds from 

 reptiles : but, further on. Prof. Parker explains that if proto- 

 vertebrate forms existed it is quite supposable that a metamor- 

 phosis may "have taken place of this and that (/«rtj/-larval 

 form into archaic reptile, ancestral bird, or primitive mammal." 

 We must therefore conclude, either that there were two kinds of 

 protovertebrates, namely, piscine and reptilian —or ichthyopsidan 

 and sauropsidan, as Prof. Parker would probably prefer to call 

 them — fundamentally distinct or preceded by common ancestors, 



