192 



NATURE 



[August ii, 1910 



cular volumes of a long series of normal paraffins, made 

 on tfie liquid substances at temperatures at which the 

 materials arc in physically similar conditions, are stated 

 in column 4. Since the valency of carbon is four times 

 that of hydrogen, it would be anticipated from the crystallo- 

 graphic conclusions previously drawn that each carbon 

 atom should appropriate four times as large a space for 

 occupation as one hydrogen atom ; the quotient of the 

 molecular volume by the valency sum or valency volume, 

 W, should consequently lead to the same value, S, in the 

 case of all the hydrocarbons. The mean value of S, 

 namely, the atomic volume of hydrogen, is thus calculated 

 as 2'q7o, and that it is constant within very narrow limits 

 is seen on comparing columns 4 and 5, the latter of which 

 states the product of the valency volume, W, by the value 

 2-970. The simple relation between the atomic volumes of 

 carbon and hydrogen in the liquid normal paraffins mdi- 

 cated in the above table was recently pointed out by Lebas, 

 and is abundantly confirmed by numerous series of deter- 

 minations in addition (o that now quoted. It is thus 

 definitely proved that the law of valency volumes, first 

 enunciated on the ground of the crystallographic evidence, 

 holds rigidly in the case of these liquid substances. 



Sufficient has been said to demonstrate that a method 

 has now been devised by means of which the vast stores 

 of accurate goniometric measurements collected by 

 crystallographers during the past century can be interpreted, 

 and that the requisite interpretation has in many cases 

 already been given. Prof. Liveing, in a discourse delivered 

 in this room nineteen years ago, suggested that crystal- 

 line forms are the outcome of the accepted principles of 

 mechanics ; the aid of these, and of these alone, has been 

 invoked to show that crystalline structures result from the 

 equilibrium of the attractive and repulsive forces radiating 

 from the atomic centres. 



RESULTS OF SOME RECENT INVESTIGA- 

 TIONS ON MAGNETIC DISTURBANCES.^ 



A N examination of the times of beginning of the mag- 

 ■^^ netic disturbance which occurred on May 8, 1902, 

 as coincidently with the Mont Pel^e eruption as can be 

 determined, revealed the interesting fact that they were 

 not the same all over the globe, being, in general, earliest 

 at European stations. The times ne.\t progressed going 

 around the earth eastwardly, the complete circuit being 

 made by the disturbance in about 33 minutes. This fact 

 led to an examination of other similar disturbances, such 

 as the one of January 26, 1903, and it was again seen 

 that this one also progressed around the earth eastwardly, 

 the time for the complete circuit being about 4 minutes. 



Mathematical analyses were next made, and it was found 

 that for both disturbances (May 8, 1902, and January 26, 

 1903) the systems of disturbance forces which it would be 

 necessary to superpose upon the earth's own magnetic field 

 were precisely of the same character as the earth's. In 

 other words, were we to assume electric currents as con- 

 stituting the disturbance systems, then, as is the case for 

 the earth's field, the currents would have to circulate 

 around the earth from east to west if they are positive 

 ones, and in the contrary direction — from west to east — if 

 they are negative or such as would be produced by moving 

 negative charges. Furthermore, for both disturbances the 

 electric currents would have to circulate chiefly in the 

 regions above the earth. ° 



For the disturbance of May 8, 1902, there were a 

 sufficient number of trustworthy determinations of the effect 

 on the vertical intensity, and accordingly it was possible, 



1 A summary of two papers presented respectively at the meeting of the 

 Washington Academy of Sciences. February 17. 1410, and at the meeting 

 of the PhiIo.sophical Society of Washington, April q, iqio. 



- See Terrestriat Magnetism nnd Atmospheric Electricity^ vol. xv , 

 pp. 9-30. In this connection it is also well to record that Dr. W. van 

 Bemmelen, in his recent investigations on " The Starting Impulse of Mag- 

 netic Disturbances " (Proceedings of the Amsterdam Academy of Sciences, 

 .^pril 24, 1903), found the following importrint fact -is applying to the Batavia 

 magnetic observatory records, 1882-99: — " Taking no consideration of the 

 slight introductory movement, 124 cases furnished for the duration of the 

 impulse : in horizontal intensity. 4*5 min.; declination, 3-2 min ; vertical 

 intensity, 12-0 min. The duration of the vertical intensity movement is in 

 general difficult to determine, as the decrease in this element keeps on mostly 

 much longer. It is important to nntice that the initial movement of D 

 slops or is inverted, whilst of H the increasing movement keeps on." 



NO. 2128, VOL. 84] 



by means of the analysis, to separate the external system 

 of currents from the internal Cbelow the surface) one ; and 

 then the surprising result revealed itself that the internal 

 currents went in the same direction as the external ones, 

 the latter being about three times the strength of the 

 former. Hence, were we to suppose that the disturbance 

 is caused by the motion of negative charges around the 

 earth eastwardly, then the internal negative currents also 

 go in the same direction, and accordingly they are not 

 currents induced in the earth by the outer system. 



If the earth's own magnetic field is likewise separated 

 into an internal system and an external one, it is also found 

 that for both systems the negative electric currents go in 

 the same direction around the earth, viz. from west to 

 east. The disturbance systems found above are therefore 

 precisely similar in character to the earth's field. It should 

 also be noted that the negative currents of the disturbance 

 progress around the earth in the same way as did the times 

 of beginning referred to above. 



We have now become acquainted with the fundamental 

 facts of observation pertaining to the simplest class of 

 m.agnetic disturbances e.xperienced by the earth — the 

 sudden beginnings of magnetic perturbations, which, in 

 accordance with van Beinmelen's suggestion, we will term 

 for brevity " S " storms. Let us see what hypotheses are 

 necessary for a physical explanation of the observed facts. 



Prof. Kr. Birkeland, of Christiania, was the first to 

 have attempted a definite physical theory to account for 

 this class of disturbances, which he termed " equatorial 

 perturbations," since they are most strongly developed in 

 the equatorial regions, as judged alone from the size of 

 the disturbance effect on the horizontal intensity. If the 

 latter element suffered an increase, the disturbance was 

 called a " positive equatorial perturbation," and if, on the 

 other hand, the horizontal intensity was decreased, the 

 disturbance was termed a " negative equatorial perturba- 

 tion." The theory for these particular disturbances is only 

 a part of the general " kathode-ray theory " developed by 

 Birkeland and Stormer to account for all classes of mag- 

 netic disturbances and of polar lights, as set forth in their 

 various papers, and especially in Birkeland's recent publi- 

 cation, " The Norwegian .Aurora Polaris Expedition, 

 1902-3," vol. i., " On the Cause of Magnetic Storms and 

 the Origin of Terrestrial Magnetism." It will be noted 

 that it is even hoped to build up a general theory of 

 terrestrial magnetism, and there is an intimation that the 

 earth's inagnetic periodic variations may likewise be among 

 the consequences of kathode rays coming from the sun 

 and entering the earth's field. 



Without question, these important contributions of 

 Birkeland and Stbnner inark a distinct advance, and the 

 student of magnetic science will find not only incentive, 

 but also a wealth of material and many suggestive facts 

 by looking over these very valuable researches. At present, 

 however, their theoretical results and deductions must be 

 regarded chiefly as qualitative. While it is made very 

 plausible that the cause of our magnetic storirs is to be 

 referred principally to kathode rays originating in the sun 

 and coming within reach of the earth's magnetic field, 

 there are a great inany questions left open which will 

 require answering before full acceptance can be given to 

 the theory in all its details. How the earth's own mag- 

 netic system is affected by a magnetic disturbance — 

 whether the intensity of magnetisation is increased or 

 decreased, if there are any after-effects, whether the currents 

 within the earth are induced ones or are the same in direc- 

 tion as those outside, &c. — are but a few of the interesting 

 and important questions to be solved. 



It seemed very desirable, therefore, that someone should 

 take up the investigation from an analytical point of view, 

 viz. to take a typical magnetic storm and analyse the 

 observed effects into spherical harmonic terms, so as to 

 determine just how much is due to outside currents and 

 how much to currents within the earth itself. 



Birkeland concluded, from a general consideration of the 

 effects of a magnetic disturbance on the vertical intensity, 

 that all storms originate from without, and it is quite 

 possible that, in the main, he may be right, but the con- 

 clusion cannot be accepted as invariably true without a 

 detailed mathematical analysis of each particular case. In 

 his first volume he accordingly proceeds on the assumption 



