4 8 4 



NATURE 



[October 12, 191 1 



simultaneously within the limits of error in the observa- 

 tions. 



When several observations of such magnetic storms 

 around the equator, obtained by .quick-run registerings, arc- 

 available, as I hope may be the case soon, this important 

 question on simultaneity will be finally determined. 



It may be of interest in connection with this to call to 

 mind that, in 1900, quick-run registerings were taken 

 simultaneously in Potsdam and at my observatory at 

 Haldde, near Bossekop. In my work " Expedition 

 Norvegienne de 1899-1900 pour 1'eTude des aurores 

 boreales," Christiania, 1901, photographs of these register- 

 ings are given which show that corresponding small sudden 

 alterations in D were simultaneous within three seconds in 

 Potsdam and Bossekop. 



According to my theories of magnetic storms, it might 

 be expected that sudden similar magnetic change:, which 

 occur in different parts of the earth arise rather simul- 

 taneously. When the sun suddenly sends forth a strong 

 pencil of kathode rays towards the earth, this pencil will, 

 owing to earth-magnetism, be broken up in such a way as 

 to form different partial systems of magnetic impulses — 

 polar and equatorial. The various groups of rays have to 

 travel different way-lengths in space before reaching 

 nearest to the earth, and may arrive at very different 

 earth-regions for the different groups. But the difference 

 in time between these various impulses affecting any par- 

 ticular locality on the earth can scarcely be more than a 

 couple of seconds, while the difference in the intensity of 

 the effects can be very considerable. We know of corre- 

 sponding phenomena in the case of aurora, as I demon- 

 strate in my first above-cited work. 



Christiania, September 29. Kr. Birkeland. 



The Library and the Specialist. 



Nature of August 17 has just come to hand, and I am 

 much pleased to see the article in it (p. 222) on " The 

 Library and the Specialist." The reference there made 

 (not quite accurately) to my own difficulties as a biblio- 

 grapher and student I gladly pass over : the troubles of 

 an individual are of little mom.ent when they are known 

 to be shared by practically all scientific men. 



The general argument in favour of reform is excellently 

 put in the last paragraph of the article, and there is no 

 need to add to it. I ask leave merely to bring things to 

 a practical issue by stating briefly and clearly what steps 

 an necessary to be taken to attain the important object we 

 all have in view. 



11) A hand-list has to be drawn up containing the names 

 of all current mathematical serials. This could be done in 

 ' few hours by any competent librarian having a mathe- 

 matical adviser within reach, the material being all ready 

 to hand in the lists given in the Jahrbuch, the Revue 

 Semestrielle, and the International Catalogue. 



(2) Six copies would have to be made of the said hand- 

 list when finally revised, and one each sent to the librarians 

 of the Mathematical Society, the Royal Society, the British 

 Museum, University College, South Kensington, and the 

 Patent Office, in order that each librarian might indicate 

 which of the serials his library possesses. From all I 

 know of these libraries, T am sure that there is not one 

 of them but would wish to help. 



1 A new list would then have to be made containing 

 the combined details provided by the six, and a copy of 

 this to be furnished to each library. 



Any serious obstacle in tin way of accomplishing this 

 scheme it is impossible for an outsider to conceive. One 

 of your influential correspondents in iqo6 seemed to imply 

 that the librarians would "stand upon the order of their 

 going." Personally, I esteem them too highlv to believe 

 this. Am on. oi three of them might fairly expert the 

 others to follow, the Mathematical Society having a claim 

 d because of the special science concerned, tli" Roval 



tj lii-eaiise of its outstanding position among scientific 

 bodies, and tin British Museum because of its unique posi- 



tmong libraries. Will none of the three risk a 

 for the work's sake? 



I fail even to see that there is a money difficulty in the 

 way. The libraries concerned are constantly being put to 

 privati individuals. But if money 

 NO. 2189. VOL. 87] 



reall) be wanted, thi least 1 can . k for is to be told 

 lie amount. Titos. MuiR. 



1 apt I 1 iwn, south Ah ■ .1 September 5. 



I am glad to be able to assure Dr. Muir and others 

 interested in the matter that steps are about to be taken 

 to carry out the plan he suggests, and to supply each of 

 the six London libraries with the list in its final form. It 

 may even be possible to draw up a more comprehensive 

 scheme, and to publish the list in a periodical readily 

 accessible to mathematicians. If the librarians will give 

 their aid, the minimum for which Dr. Muir appeals will 

 be accomplished before the meeting of the International 

 Congress in 191 2. 



The Writer of the Arth 1 



Two Undescribed Giraffes. 



A piece of tanned giraffe-skin in my possession, which I 

 intend to present to the British Museum, indicates, appar- 

 ently, an undescribed race of the netted giraffe (Giraffa 

 reticulata) of Somaliland and British East Africa. That 

 species is characterised by the markings taking the form 

 of a coarse network of narrow white lines on a liver-red 

 ground, the dark meshes being large and quadrangular on 

 the neck, but becoming smaller and more irregular in 

 shape on the body. There may be small white spots in 

 the centre of the dark patches, which are otherwise 

 uniformly coloured, even in adult bulls. In the piece of 

 skin referred to above, which is from the forepart of the 

 body, and came from British East Africa — probably thi 

 Kenia district — the white lines are rather wider and the 

 dark areas smaller and brownish rufous, with a tinge of 

 blackness, and a distinct blackish streak or star in the 

 centre. For this giraffe, which in a slight degree tends to 

 connect reticulata with the eastern forms of camelopardalis, 

 the name G. reticulata nigrescens will be appropriate. 



The second race is typified by a mounted adult bull from 

 north-eastern Rhodesia, the skin and part of the skeleton 

 of which were presented to the British Museum by Mr. 

 H. S. Thornicroft, Native Commissioner of the Petauke 

 district. This giraffe — a member of a single isolated herd 

 — is characterised by the low and conical frontal horn, the 

 grey colour and scattered spotting of the sides of the fact . 

 the chestnut-brown forehead, deepening into black on the 

 tips of the horns, the absence of a distinctly stellate pattern 

 in the neck and body spots, which are light brown on a 

 yellowish-fawn ground, and the uniformly tawny colour of 

 the lower portion of the limbs. This giraffe, which I pro- 

 pose to call G. camelopardalis thornicrofti, appears to be 

 related to the Kilimanjaro G. c. tippelskirchi, but differs 

 by the more compact frontal horn, the brown, in place of 

 grey, forehead, and the uniformly fawn lower part of the 

 legs, the latter being whitish in adult bulls, but fawn and 

 spotted in cows and young bulls. I have to thank the 

 trustees of the British Museum for permission to describe 

 this specimen. R. Lydekker. 



The Distastefulness of Anosia plexippus. 



In " Essays on Evolution," p. 274, 190S, Prof. Poulton 

 directed attention to the instance of mimicry amongst 

 Lepidoptera supplied by the American Danaine, Anosia 

 plexippus, otherwise known as Danaida archippus, and its 

 mimetic species. It occurred to me, therefore, that it 

 would be interesting to test the distastefulness of this 

 butterfly. This I was enabled to do through the kindness 

 of Mr. F. W. Frowhawk, who at my request sent me a 

 newly emerged female on September 22 of this j 



The following are the results of my experiments. Two 

 Indian shamas (Cittocincla macrura) in succession tasted it. 

 but left it alone after one or two peeks. It was then 

 taken by an Indian sibia (Sibia capistrata), which quickly 

 dropped it. A red-vented bulbul (Pycnonotus haemorrhous) 

 then pounced upon it. with the same result. A ground 

 thrush (Geocichla cyanonotus) tried it, but soon left it. A 

 mynah (Croatia intermedia) took it, but quickly let it fall. 

 Two South African bustards (Otis ludwigi) persevered for 

 a long time, but finally rejected it. A kagu (Rhinochaetus 

 iubatus), a kind of rail or crane from New Caledonia, 

 behaved in the same way, shaking his head after each 

 peck. An Australian water-hen (Tribonyx ventralis) and 



