CHAPTER I. 



PRELIMINARY REMARKS CONCERNING OUR MAGNETIC RESEARCHES. 



13. Our Aim and our Method of Working. It has, as is generally known, been ascertained 

 that there exists a close connection between sunspots and the magnetic conditions upon the earth. As 

 early as 1852, SABINE discovered, almost simultaneously with GAUTIER and WOLF, that in years when 

 sun spots were numerous, the magnetic storms were more frequent and more violent than in years when 

 there were few sun-spots. By comparison with the period of magnetic oscillations pointed out by LAMONT 

 in 1850, it was discovered that maxima and minima in the magnetic period coincided with maxima and 

 minima in the sun-spot period. 



These and kindred circumstances have since been carefully investigated. It has been found that 

 the magnetic constants have secular variations, which, with convincing exactitude, follow the simultaneous 

 variations in the occurrence of sun-spots; and further, that there are periods for the frequency of 

 magnetic storms and for aurora, which correspond with the so-called undecennial period of the sun-spots. 

 From the very first, when these relations were discovered, attempts were naturally made to find 

 out the connecting mechanism between these phenomena, so that the physical cause might become clear; 

 but these have not as yet been entirely successful. 



It has gradually come to be acknowledged that aurora and magnetic perturbations should be regarded 

 as rather moderate manifestations at present the only ones there are for us to observe of an un- 

 known cosmic agent of solar origin, and quite different from light, heat or gravitation. It has long been 

 supposed that this unknown agent was in some way or other of an electrical nature. The elder BECQUERF.L 

 even, gave expression to some very interesting ideas on this subject. 



With regard to the magnetic storms in particular, it is clear that the observed changes in force 

 can be formally explained by an infinity of assumptions with distribution of fitting agents that generate 

 magnetic forces; but nevertheless it may safely be said that up to the present not one definitely 

 formulated hypothesis has been put forward, which explains all the phenomena so simply and naturally, 

 that the hypothesis becomes satisfactory. 



In the following pages it will be shown how far I have succeeded in explaining the above-mentioned 

 and several kindred relations, starting with the assumption which, viewed from the present standpoint 

 of natural philosophy, is a legitimate one, namely, that the sun, and especially the spots on the sun, 

 send out into space cathode or kindred rays. 



In order to gain definite conceptions of the effect of such rays in the vicinity of the earth, I have 

 again and again had recourse to analogisms from my previously-described experiment in which a magnetic 

 terrella is suspended in a large discharge-tube ('), and exposed to cathode rays. 



The experiment, which was originally made for the purpose of finding points of support for a 

 hypothesis for the formation of aurora, has proved a veritable mine of wealth, in which I have constantly 

 made valuable discoveries. 



(') Expedition Norvegienne de 1889 1900, etc., I. c., pp. 39 et seq. 

 Rirkeland, The Norwegian Aurora Polaris Expedition, 19021903. 



