October 7, 1909] 



NATURE 



425 



cuines the independent State of Nepal, of which 

 nothing at all is known, and it is only in the British 

 territory and the native States under British control 

 at the north-western extremity of the range that the 

 geolog\- is known, even approximately There is, con- 

 sequently, a tendency to extend the knowledge of this 

 legion to the rest of the range, and to draw conclu- 

 sions which are only doubtfully applicable. 



This tendency has not altogether been avoided, and 

 the lengthy discussion of the age of the unfossiliferous 

 sedimentary rocks of the Simla region seems to give 

 this subject an importance which it does not possess, 

 especially as, in the end, it is left in a state of little 

 less uncertainty than before. The only clue to the age 

 of these rocks is the fact that they contain a series of 

 beds, the Blaini, which is generally acknowledged to 

 present unmistakable signs of glacial origin. At one 

 time this series was regarded as of Permian age, but 

 this explanation is rejected, and the Blaini series is 

 correlated with the pre-Cambrian glaciation which has 

 been studied and described in Africa, China, Australia, 

 and, we may add, in Norway. Mr. Haj'den argues 

 with great plausibility that the complete absence of 

 any trace of fossils in a great thickness of rocks, 

 which might well be expected to contain them, and 

 their abundance in the great series of deposits on the 

 other side of the snowy range, is more reasonably ex- 

 plained by a difference in age than in conditions of 

 deposition. This reasoning we may accept, and 

 acknowledge that the Blaini tillites are more probably 

 pre-Canibrian than Permian in age, but the possibility 

 that the rocks of the Simla area are a flysch facies of 

 the fossiliferous sediments of Spiti must be borne in 

 mind, and, until less equivocal evidence is adduced, the 

 problem must remain unsolved. 



With this exception the work is a well-balanced 

 summary of the geology of the Himalayas, useful to 

 those who wish to have the leading facts put briefly 

 and clearly, and also, by the copious references to 

 original authorities, invaluable as a guide to more 

 detailed study. 



Elementary Physiol'jgy for Teachers and Others. By 

 \V. B. Drummond. Pp. viii+198; illustrated. 

 (London : Edward .Arnold, 1909.) Price 2s. 6d. 

 This is a useful little book of its kind, elementary, as 

 its title implies, and correct in its details, an element 

 so often lacking in similar works. Like other books 

 of its class, it necessarily contains a good deal of what 

 is anatomy rather than physiology, and it chiefly 

 differs from its competitors in pointing out the appli- 

 cations of physiology in the health, well-being, and 

 training of children. This is by no means an unim- 

 portant point, seeing that the work is written for 

 school teachers. W. D. H. 



Evolution: A General Sketch from Nebula to Man. 

 By Joseph McCabe. Pp. vii-f-128. (London: 

 Milner and Company, Ltd., n.d.) Price iS. net. 



The author of this little book defines his aim as being 

 " chiefly to present a panoramic view of the develop- 

 ment of the world — especially the world that lies close 

 about us — by a conscientious use of the results of 

 many sciences, and aided by a personal acquaintance 

 ■during many years with both telescope and micro- 

 scope." The style is interesting, and the slight 

 sketch provided may send a few general readers to 

 first-hand authorities for further information. The 

 language is not always precise ; for instance, we find 

 " refractory liquid fire," " a lowering of climate," and 

 so on ; but on the whole the volume may serve a useful 

 purpose by introducing non-scientific readers to some 

 problems of inorganic and organic evolution. 

 NO. 2084, VOL. 81] 



LETTERS TO THE EDITOR. 



[The Editor does not hold himself responsible for opinions 

 expressed by bis correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other fart 0/ Nature. 

 No notice is taken of anonymous communications.] 



Magnetic Storms and Solar Eruptions. 



Referring back lo the Electrician of nine years ago 

 (December 7, 1900), I find that, following up a sugges- 

 tion of G. F. FitzGerald made in 1S93, 1 promulgated a 

 view of major magnetic storms which events have con- 

 firmed. See, for instance, Mr. Maunder 's paper in Men. 

 Not. R.A.S. for 1904, vol. l.xv., p. 33. 



What I have to point out is that a stream or beam of 

 electrons ejected from the sun and passing near or over 

 the earth would cause magnetic perturbations of the kind 

 required — positive as it approached, zero as it passed over, 

 negative as it receded ; with many minor disturbances 

 superposed due to variations of density, as well as others 

 due to the effect of particles caught by the atmosphere. 



Such a beam or stream of electrified particles is 

 essentially a magnetic cyclone, and the changes in mag- 

 netic force as it travels past any locality bear a fairly 

 close analogy with the changes in wind-velocity during the 

 passage of an atmospheric cyclone. 



The relative speed of such a solar beam, as it overtakes 

 the earth, follows from the sun's angular velocity, and is 

 210 miles a second. 



Earth currents would, in the main, be induced as it 

 approached and checked as it receded. 



The rotation of the earth in the magnetic field of such 

 a stream is too slow to be effective : though locally in the 

 neighbourhood of six o'clock an intense ray of the main 

 beam might generate east and west currents. 



Now magnetic disturbances recorded during the recent 

 storm, and quoted by Dr. Chree in the Times and else- 

 where, indicate a declination deflection of ij degrees, 

 followed by a reversed deflection of the same amount— all 

 wilhin a quarter of an hour. 



Tliis means — on the above theory — that the main beam 

 took this time to traverse the place, so that the breadth 

 of the beam was comparable to twenty times the earth's 

 diameter. No doubt it is diffused, at this distance from 

 the sun, by internal repulsion of the particles. 



The intensity of field which would give the above de- 

 flection is approximately one-fortieth of that of the earth's 

 horizontal intensity, or, say, 0004 C.G.S., as the order 

 of magnitude. 



Taking these data, together with the known charge and 

 velocity of electrons in kathode rays — say e = io-'° electro- 

 magnetic C.G.S. units, !(=io' centimetres per second — 

 let us reckon the closeness of the crowd of particles in the 

 beam necessary to account for the observed force. 



The magnetic intensity at any place, distant r from the 

 axis of a linear stream of sectional radius a and current 

 density 7, is given by the following expressions ; — 



where " 

 of the stream. 

 This gives 



y = n^eu, 

 the number of particles per cubic centimetre 



the beam, so that 

 the other data just 



>-H 



' 2Ta'-eii 

 so taking a place just grazed by 

 r = a = 20X2,'7rX 10°, and putting in 

 cited, we get 



_ o' 0O4 



"'" 80^59 X 10-" 

 = o'oo5 per c.c. , 

 or, say, five electrons per litre, on the average, all through 

 the beam. I regard this as a modest and not unlikely 

 estimate of crowdedness. The amount of matter ejected 

 from the sun in this beam is insignificant, being less than 

 a couple of tons per week. 



The total current equivalent of such a beam is six 



