458 



NATURE 



\ March 17, 1881 



selenium was then coated with shell-lac varnish, and about two 

 hours afterwards again tested in the same manner as before, when 

 the light was found to produce a deflection of 220 divisions, or 

 more than twice the previous amount. The action of radiant 

 heat was similar to that of light in the case of this particular 

 specimen, but I have little doubt that any specimen may be 

 .■enderei more sensitive to light by coating it with varnish or 

 lampblack. I hope that this suggestion will prove of service to 

 those phil jsophers who may aspire to "hear a beam of light" 

 or to " see by electricity," and shall be glad to hear that such 

 has been the case. Herbert Tomlinson 



King's C'^Uege, .Strand, March 7 



Cave Animals and Multiple Centres of Species 



The readers of Secnper's " Existenzbediugungen der Thiere," 

 now translated into English, will find (vol. ii. p. 268 of the 

 German edition) an interesting discussion on the question of 

 monophyletic or polyphyletic evolution of species, the author 

 decidedly inclining to the latter hypothesis. Considering that at 

 the root of the manifold and difficult problems here involved, 

 there is the relatively simple one of single or multiple centres of 

 each species in a biographical sense, I take leave to ask the 

 following question, hoping for an answer from among your 

 readers verged in these matters. 



To me it seems impossible to maintain the single centres of 

 species in a strict and definite sense without also maintaining the 

 single progenitor of each species, which latter view, formerly 

 considered as a necessary assumption, has been given up by Mr. 

 Darnnii in Chapter IV. of the later editions of the " Origin of 

 Species" (sth ed. p. 103, 104). Of course the acceptance of 

 single centres, in the sense of more or less restricted areas of 

 origination, may remain valid for the vast mijority of species— 

 but this is very different from considering it, once for all, as "a 

 necessary consequence of the adoption of Darrtinian views," as 

 has been formerly said by Mr. Bentliam (Nature, vol. ii. 

 p. 112). 



Now, I have sometimes thought that there might be a test for 

 th&possihUity of multiple centres, which, eventually, would amount 

 almost to an experimental demonstration — namely : whethei- tlwe 

 are cases of the same species of liliiid animals occurring in difiirent 

 caves distant from and without subttrranean communication Ziuth 

 each other? Should such cases occur it would be m^st improbable 

 that the animals in question had been transported from one cave 

 to the other in the mo lifted state, and most probable that they 

 had been independently evolved in each cave from identical 

 species which entered 'it from \\ithout. I formerly noted one 

 instance perhaps in point, viz. a statement of Prof. Cope's 

 (Nature, vol. vii. p. 11) that "the blind fi,h of the Wyandotte 

 Cave is the same as that of the Mammoth, the Amilyopsis 

 sfelaeus, Dekay," but I am not aware whether subterranean 

 communication is, or has been, impossible in this instance. 

 Perhaps more decisive cases have become known of late ? 



Freiburg im Breisgau, March 4 D. Wetterhax 



Prehistoric Europe 



Will you kindly allow me to con-ect a clerical error in my 

 letter which appeared in Nature, vol. xxiii. p. 433. For 

 " ' hash-up ' of ///,' species," read " ' hash-up ' of species." A 

 nunber of the species from the Upper or Interglacial Bone-bei 

 of Mont Perrier (and some of which are mentioned in my letter) 

 are of course too characteristically Pleistocene to be claimed by 

 Prof. Dawkins as Pliocene forms, and do not therefore appear 

 in his list of Upper Pliocene species to which I referred. 



Perth, March 14 James Geikie 



Measuring the Height of Clouds 



In Nature, vol. xxiii. p. 244, Mr. Edwin Clark gives a 

 method whereljy the height or distance of clouds may be 

 measured. This end has already been attained by me, several 

 years ago, and I believe with adequate .success. I have also 

 worked out the method in detail, so that its practical realisation 

 no longer offers any difficulty. It is very simple and easy, and 

 the apparatus (" nephoscope"; is not difficult' to make. A full 

 description of tlie nephoscope will be found in the Zeitschrift der 

 Oestei-reich. Ges.fur Meteorologie, eAiiei by Jelinek and Hann, 

 1^ ■ j]- P- 337. in so far as the instrument seives for measuring 

 the direction and velocity of the passage of clouds. In order also to 

 ascertain the alisolute height of clouds (N. B. all without calcula- 



tion) I have introduced an improvement. This and a guide to 

 practical use I have published in the same Zeitschrift (vol. ix. 

 September, 1874, pp. 257.61). I believe Mr. Edwin Clark will 

 find in the article referred to his idea fully worked out. 



C. Braun, 

 Kalocsa, Hungary, March 3 Director of the Observatory 



Occultation of 73 Piscium 



I OBSERVED here this evening the occultation of 73 Piscium 

 by Jupiter, which was predicted in your "Astronomical Column " 

 under the date December 23, 1880 (Nature, vol. xxiii. p. 183). 

 At ih. 52m. 30S. G.M.T. the star was hanging on the limb of 

 the planet, and by ih. S4m. it had entirely disappeared. 



The phenomenon strongly resembled the occultation of a 

 satellite, except that the disappearance was more rapid. But it 

 was not instantaneous as I had expected. The planet and .star 

 appeared to cohere for about one and a half minute. The 

 contrast in their colours was very marked, Jupiter appearing of 

 a yellowish tinge, while the star shone out white like a diamond. 

 During the occultation the red spot was on the planet's disk, 

 and its following end was in about the same meridian as the 

 point of the star's occultation. 



I had no micro.naeter, but I inclose a diagi-am showing the 

 estimated points of occultation and reappearance. 



foiiU of 

 reappear-cm ce 



The G.M.T. of reappearance was 2h. 44m., when the star 

 was again observed to hang on to the planet's limb. 



The telescope used was a 4} inch refractor by Cooke 

 equatorially mounted, with a power of 96. 



The planet was well placed for observation, -being nearly In 

 the zenith. 



Before and after the occultation Jupiter appeared as if with 

 five moons, the star being almost indistinguishable from the 

 satellites. 



As the occultation could not be observed in Europe these few 

 notes may possibly prove of some interest. 



A diagonal (prism) eyepiece was used in making the sketch. 



Meean Meer, Lahore, February 3 H. CoLLETT 



Colours of British Butterflies 



Most of the protectively coloured British butterflies pair either 

 on the ground as the " Blues," or on low herbage as the majority, 

 or on the leaves of trees, as'someof the " Hair-streaks," and with 

 closed wings. The wings of both sexes are usually opened as 

 widely as possible immediately before copulation. 



I have been struck by the fact, which I may mention in refer- 

 ence to the remark of Mr. J. Innes Rogers (Nature, vol. xxiii. 

 P- A3S)' ''^''^ I have never seen the " peacock " attacked by any 

 British bird, and I have often watched him flaunting his colours 

 in the presence of shrikes, flycatchers, and other — one would 

 imagine dangerous —company. W.Clement Lev 



Ashby Parva, Lutterworth, March II 



Lecture Representation of the Aurora Borealis 

 I HA\£ recently employed a simple device for giving to an 

 audience a vivid ilea of an aurora, and that has been to paint a 



