April 13, 191 1] 



NATURE 



21 



cules of a gas and to produce photochemical action. The 

 number of ions produced per unit length along the path of 

 the a particle has its maximum very near the point where 

 it loses its ionising power. The j3 particles, however, are 

 almost completely scattered in the first thin layer of matter, 

 and inside it the radiation broadens out in all directions, 

 and any trace of the direction of the impinging rays is 

 soon lost. 



In the aurora, according to Birkeland's theory, we are 

 actually examining the luminosity produced when the 

 electric radiation strikes the upper strata of the atmo- 

 sphere, and from the form and structure of the luminosity 

 we should be able to examine the way in which the solar 

 radiation is absorbed by matter. 



One of the most conspicuous forms of aurora are the 

 draperies, of which an illustration is given in the accom- 

 panying figure. We notice the straight-lined structure. 

 That the draperies are formed by something coming 

 towards the earth from outside will be evident to all who 

 have witnessed their formation. On March 27, 1910, the 

 writer had the opportunity of examining a most brilliant 

 aurora from the mountains of " Jotunheimen." Brilliant 

 draperies were formed, and they could be seen actually 

 falling down in the direction of the streamers, one bundle 

 adding itself to another in rapid succession so as to form 

 long spirals and bands. Now the structure of the 

 luminosity is just as would be expected if the draperies 

 were formed by a type of rays showing an absorption like 

 that found for the a rays. Looking at the luminosity 

 along the transverse streamers, we shall always notice that 

 the intensity gradually increases downwards, but stops all 

 of a sudden, just as it is found for the ionisation produced 

 by an o particle along its path. 



I do not mean to say that it is exactly a rays or charged 

 helium atoms which produce draperies, but I think that 

 the similarity in absorption strongly points to a similarity 

 in type of radiation — in other words, that the rays pro- 

 ducing the draperies are of atomic size and carry an electric 

 charge. 



The fact that the draperies occur mostly on the evening 

 and night side of the earth should, according to the law 

 of the magnetic deflection, require a negative charge of 

 the rays ; but such rays may well be possible, for, as we 

 know, Sir J. J. Thomson has found that accompanying 

 the positive rays in a vacuum tube there are other rays 

 formed by atoms, but carrying a negative charge. 



In view of the fact that a number of the same spectral 

 lines are found in the corona and the aurora spectrum, 

 which belong to the rare gases, it would be natural to 

 suppose that these inert gases, e.g. argon, neon, xenon, 

 krypton, helium, and possibly coronium, are forming the 

 carriers of the " electric radiation " producing the 

 draperies. 



The existence of such radiation does not in any way 

 exclude the existence of corpuscular rays ; these may be 

 the cause of the auroral " arch," which has just the 

 diffuse appearance to be expected from the law of absorp- 

 tion of the /3 rays. Further, the magnetic disturbances 

 may to a great extent be due to radiation of the j3-ray 

 type. L. Vegard. 



University of Christiania, March 16. 



The Velocity of Earth Movements caused by the 

 Messina Earthquake. 



I AM deeply indebted to Prof. J. Milne, F.R.S., who, in 

 Nature of March 2-?, did me the honour of directing the 

 attention of scientific men to my memoir on the velocity 

 of earth movements caused by the Messina earthquake. 

 \s the notice contains some remarks on my work which 



cjuire a little explanation, I beg to be permitted to state 

 iv views here. 



According to some seismologists, the position of the hypo- 

 I fntre is at the intersection of an asymptote to Schmidt's 

 liodograph, with a vertical ordinate drawn through its 

 apex. It seems to me, therefore, that the absence of any 

 measurable flexure in the curves may really mean that the 

 hvpocentre of the Messina earthquake was very shallow. 

 Ihat is, however, a matter of opinion about which seis- 

 mologists can easily be divided, and I have no desire to 

 insist on this subject. 



Prof. Milne assumes that I divided the large-wave phase 



NO. 2163, VOL. 86] 



of the seismograms into three parts, called L,, L,, Lj, 

 being Lj the commencement of maximum motion, Lj the 

 maximum movement itself, and L, the phase which travels 

 the slowest. He adds that if this is to be accepted as a 

 definite and recognisable phase in a seismogram, there 

 seems to be no reason why we should not also accept many 

 other phases, which may be indicated by the letters L^, 

 L-, Lg, &c. The remark is of interest, but I deserve 

 neither praise nor blame for the division of the large- 

 wave portion of seismological registrations. Prof. Milne 

 well knows that the division of the principal portion 

 of a seismogram into six groups was done by Prof. Omori, 

 analysing the registrations obtained at Tokio, and such a 

 division is now accepted by almost all seismologists. In 

 my memoir, L; indicates the commencement of the initial 

 phase ; Lj and L3 are respectively the commencements of 

 the slow-period and of the quick-period phases of the prin- 

 cipal portion of the registrations, according to Prof. 

 Omori 's division. 



Instead of considering as a whole the large-wave phase, 

 which involves some uncertainty (as often the commence- 

 ment of the principal portion is assumed to be on Omori 's 

 initial phase and at other times the commencement of the 

 same principal portion is referred to the slow-period phase), 

 I tried to distinguish in all seismograms the first three 

 groups of the large-wave phase, L,, Lj, L3. I am not 

 dissatisfied at having done this, because I have obtained 

 some results which I think are not without importance for 

 physical seismology. 



I conclude by expressing my warmest thanks to Prof. 

 Milne for his notice and for the valuable article on the 

 necessity of restoring the Messina Observatory contributed 

 by him to Nature of February 16. 



Messina, March 30. G. B. Rizzo. 



PROM THE NIGER TO THE NILE ACROSS 



AFRICA.' 

 |~\R. KARL KUMM (whom, from the indirect state- 

 '-^ merits made in his book, we take to be of Swiss 

 origin, and who now seems to be for all practical pur- 

 poses an Englishman) assisted to found the Sudan 

 United Mission in 1907-8. This mission was expressly 

 intended to work in the Nigerian and Egyptian Sudan 

 to counteract the Moslem advance, and Christianise 

 the pagan tribes of negroes not as yet influenced by 

 the Muhammadan religion. His previous acquaint- 

 ance with Africa (according to the statements made 

 in his "exordium") has been considerable. In 1899 

 he had visited "the southern oases of the Libyan 

 Desert," and had travelled a considerable distance on 

 the way to Darfur. In 190 1 he travelled in Nubia. 

 In 1904 he journeyed from Tripoli southwards into the 

 mountainous region north of Fezzan and studied the 

 Hausa language. In 1904-5 he led an expedition of 

 investigation into northern Nigeria. In the two fol- 

 lowing years he visited America and South Africa to 

 arouse interest in his mission and secure data as to 

 the advance of Islam in the direction of the Zambezi. 

 On his return from South Africa he visited Portu- 

 guese East Africa, Mombasa, and made a hasty 

 journey to Uganda. 



In October, 1908, he left Liverpool with seven mis- 

 sionaries of the newly formed Sudan United Mission 

 to visit or to found mission stations in northern 

 Nigeria, and establish a home for freed slaves. He 

 further intended, if practicable, to cross Africa along 

 the border-line between Islam and paganism. 



The book under review is the result of this last 

 journey, which extended from Forcados, at the mouth 

 of the Niger, along the course of the Benue to the 

 Musgu country on the Shari. thence up the Shari River 

 to Fort Archamliault, and from that point along the 

 line of water-p.nrting (more or less) between the Shari, 

 the Congo, and the Nile. He emerged into some- 



1 " From Hau.saland to Egypt, throuah tVe Siid.Tn." Pv Dr. H. Karl W. 

 Kiimm. Pp. xiv+32^. ( Lor don : Constable and Co., Ltd., 191c.) Price 

 i6s. net. 



