6o6 



NA TURE 



[April 28, 1892 



states, to be regarded in the light of an abstract of a series of 

 more extended papers published in the Entomologist. The 

 papers in the latter publication from their title led us to suppose 

 that Mr. Coste had made some contribution to our knowledge 

 of the chemistry of insect pigments. I read them from month 

 to month in the hope of getting new light on this subject, 

 which is of such general interest to both chemists and 

 biologists : I regret to say that I have been grievously 

 disappointed. The experiments thus far described amount 

 simply to the fact — not altogether astonishing — that 

 strong chemical reagents modify the colours of Lepidop- 

 terous pigments or in some cases dissolve them out of the 

 wings. The bearing of these observations on the chemistry of 

 . the pigments is so remote as to be practically useless until we 

 know something of the chemical nature of these pigments. The 

 methods adopted by Mr. Coste are not likely to advance our 

 knowledge in this direction very much, and it is certainly re- 

 markable that in treating of yellows he makes no reference ^ to 

 the only real contribution to the chemistry of Lepidopterous 

 pigments, viz. the experiments made by Mr. Hopkins, and 

 published in the Proceedings of the Chemical Society in 1889. 

 Mr. Coste is no doubt acquainted with those South American 

 Papilios with a large red spot on the hind wing, which spot 

 loses its red colour and becomes of a brilliant metallic bluish 

 green when the wing is tilted so that the incident and reflected 

 rays form a very wide angle. The colour is in this case doubt- 

 less a mixed result, partly due to pigment and partly to inter- 

 ference. Now, anyone who has observed this and other similar 

 colour phenomena in insects might describe his observations as 

 contributions to the physics of insect colours. If he thought 

 proper to adopt this course, he would be misleading physicists. 

 The observation of the bare facts is as much a contribution to 

 the physics of insect colours as the statement that a rainbow can 

 be seen in the sky is a contribution to the physics of illuminated 

 water-drops. It seems to me that Mr. Coste's experiments bear 

 the same relationship to the chemistry of insect colours that the 

 mere observation of interference colours in insects bears to the 

 physics of insect colours. 



Quite independent of the facts recorded by Mr. Coste is the 

 interpretation which he puts upon them. Here I must de- 

 cidedly express dissent. It cannot be admitted, because by the 

 action of certain reagents green is changed into yellow or red 

 into yellow, that this indicates the evolution of green or red 

 from yellow. There is no evidence that this result is a reversion 

 effect at all. The analogy between the action of strong acids 

 in modifying the colour of an animal pigment and the effect of 

 true reversion is forced, and has no parallel in natural pro- 

 cesses. Hot water is a chemical reagent ; by its action on the 

 brown pigment of the lobster the latter becomes red. If from 

 this observation I drew the inference that the ancestral lobster 

 was red, and that the hot water produced a reversion effect, I do 

 not think that Mr. Coste would agree with me. 



R. Meldola. 

 Oxford, April 24. 



Eozoon. 



Mr. Gregory has, I fear, slightly mistaken the meaning of 

 nay remarks, which were intended rather to excuse than to blame 

 him. The specimen of Eozoon collected by the late Mr. 

 Vennor at Tudor was figured in connection with my paper of 

 1867 as a type specimen, in so far as macroscopical characters 

 are concerned ; but it does not follow that slices from specimens 

 less perfect in that respect, and now in my collection, may not 

 be more instructive as showing minute structures. I may refer 

 in this connection to the three specimens from Tudor and Madoc 

 (Madoc being in the same formation with Tudor) figured by 

 Dr. Carpenter in our original paper in the Journal of the 

 Geological Society, vol. xxiii., pi. xii., Fig. i. If anyone will 

 take the trouble to compare these with the figures in Mr. 

 Gregory's paper in the same Journal, vol. xvii., he will have a 

 singular and impressive illustration of the different ways in 

 which things supposed to be the same may appear to observers 

 of different types. 



Mr. Gregory is in error in supposing that he could see in the 

 cases of the Peter Redpath Museum my specimens from Tudor 

 and Madoc. I have not yet been able to place there any portion 

 of my microscopic cabinet of Eozoon; but only a few hand 



'_ At least in Nature : I have not the Entomologist at hand where I am 

 writing. 



NO. IT 74. VOL. 45] 



specimens sufficient to show students the ordinary types of the 

 fossil. ' '^ 



As to the Laurentian age attributed to the Tudor beds, I have 

 already explained that this I subsequently regarded as an error^ 

 and so stated not long after the date of the paper of 1867. I 

 now regard them as less ancient, though of pre-Cambrian age. 



I shall be happy to show to anyone my little collection from 

 Tudor and Madoc, including specimens in which Carpenter 

 detected the canal system ; but of these particular specimens I 

 have unfortunately no duplicates for distribution, and would 

 prefer to exhibit the slices in the modes I have found best 

 suited for the development of the structures ; as otherwise there 

 might be some doubt whether the resulting impressions would 

 more resemble Mr. Gregory's figures or Dr. Carpenter's. 



Montreal, April 6. J. William Dawson. 



The Theory of Solutions. 



I AM glad to see that as to the main point, the character of 

 the "gaseous laws" of solutions, there seem to exist no more 

 differences between Mr. Rodger and me. For Mr. Rodger, in 

 his letter on p. 487 of Nature, limits his remarks to some 

 dialectical expressions, to cover an honourable retreat. I wish 

 not to follow him on this way, because it is an endless one. 



As to the application of van der Waals's formula on solutions, 

 Mr. Rodger is now forced to confess that this application is not 

 so " meaningless " as he has formerly written; but he asserts 

 that, shortly spoken, the form of application given in my book 

 is so. To say the truth, if I have to choose, as in this case, 

 between the agreement of a formula with Mr. Rodger's opinion, 

 and the agreement of this same formula with experiment, I prefer 

 the latter. \v. Ostwald. 



Leipzig, April 12. 



Physiological Action of Diminished Atmospheric 

 Pressure. 



With reference to the effect of diminished atmospheric 

 pressure on the vital powers, alluded to in Prof. Bonney's 

 review of Mr. Whymper's " Travels among the Great Andes of 

 the Equator" (Nature, April 14, p. 561), I do not know 

 whether it is worth while recalling the well-known fact that 

 numerous passes in the Himalayas, ranging from 17,000 to 

 19,000 feet, are habitually traversed by the hillmen, in the 

 summer, with their flocks of sheep and goats carrying borax, &c. 

 The highest pass is said to exceed 20,400 feet. In the same 

 mountains Messrs. Schlagintweit reached an altitude of about 

 22,200 feet (Proc. As. Soc. Bengal, January 1866), while Mr. W. 

 W. Graham ascended to 23,500 feet in 1883 (Nature, September 

 1 1, 1884). I have myself, on several occasions, been to elevations 

 of 17,000 to 19,000 feet, and beyond shortness of breath when 

 climbing, never experienced any ill effects except once, when I, the 

 four plainsmen with me, and three out of a considerable number 

 of hillmen, felt severe headache during the evening after crossing 

 a high pass. My companion on one trip, however, almost 

 invariably suffered very severely from mountain sickness under 

 similar circumstances. F. R. Mallet. 



18, The Common, Ealing. 



Sensitive Water Jets. 



A form of this effect lately presented itself, which seemed in 

 some ways new. A thin jet, 5 feet high and arched so as to be 

 3 feet at the base, was falling in a feathery spray. At 13 feet 

 distance a small Wimshurst machine was set going : not 

 instantly, but after two minutes, the spray gathered itself up 

 almost into one clear line : although the jet was turned up and 

 down and the machine was discharged the falling water would 

 not resolve itself again into spray for fifteen or twenty minutes. 

 It is difficult to imagine the medium for this action : it is too 

 indefinite, perhaps, to suppose that an indicator is found for the 

 trembling of a disturbed ether while it is dying down. 



The well-known experiment is not known enough, for it is not 

 often described in books. Take a glass rod, electrified ever so 

 little, to a certain point ; at once the jet collects itself ; a slight 

 move away brings back the old disorder, while an inch nearer 

 makes things much worse. It is a striking illustration to 

 help one to imagine what the electrical forces of the air may do 

 We can perhaps understand those thick thundery rain-drops, 

 that almost allow us to pass between them while they are giving 

 friendly warning of what will come. W, B. Croft. 



Winchester College, April 14, 



