726 B1KKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 1903. 



vations, but taking the average of several days, found curves for the diurnal variation of earth-currents 

 which seemed to show some similarity with corresponding magnetic variations. The similarity is not a 

 striking one, and it is doubtful how a similarity which is not shown in simultaneous observations should 

 be interpreted ; so it was at last to be considered as rather doubtful whether the diurnal variation of the 

 earth's magnetism was due to earth-currents. 



Thus the actual test of the theory of the electric origin of the earth's magnetism had not given 

 any trustworthy confirmatory results. 



Then an event occurred which should show definitely that a connection of some kind existed 

 between the variation of the earth's magnetism and earth-currents. 



From the 2gth August to the 3rd September, 1859, a great magnetic perturbation took place, 

 accompanied by aurora borealis, and simultaneously the telegraph-lines were disturbed by currents of an 

 extraordinary strength, which were observed at the most various parts of the world. 



This event gave a great impulse to the study of earth-currents. Earth-current observation 

 carried on for several years on the English telegraph-lines, and were collected and worked out In 

 C. V. WALKER^). 



About simultaneously earth-current measurements were undertaken by LAMCNT^). 



In his first publication, Walker treats the earth-currents observed during magnetic disturb;.) 

 In spite of the fact that the two phenomena accompany each other, he does .not venture to draw the 

 conclusion that magnetic storms are entirely caused by earth-currents. His statements are of special 

 interest when looked upon in the light of recent research. He says( 3 ): "Other influences than those 

 exerted by electric currents upon magnets may or may not be in play; but one thing is very certain, 

 that at least a large portion of the motion presented by the magnetometers on storm days is connected 

 with the then prevalence of earth-currents ; and doubtless some portion of all the more regular and less 

 violent disturbances may be more or less due to the same causes. At any rate, although we arc 

 siderably in the dark as to the forms of force in operation to make up the whole of the causes con- 

 cerned in magnetic disturbances, we are yet quite certain that the current form of force is at least in 

 part concerned." 



In a subsequent work Walker deals with the ordinary currents found on undisturbed days, lie 

 finds that the currents observed are real earth-currents and are not due to the earth-plates or other 

 local conditions. They are not equally frequent in all directions, but appear mainly in the two opposite 

 quadrants N-E and S-W. This result has been confirmed by later observers. 



Lament seems to be of the opinion that magnetic storms are produced by earth currents, but he 

 does not consider it to be proved that all variations in the earth's magnetism are due to earth-am 



Up to this time all observations had been. carried out by taking readings at intervals. In this way 

 it was very difficult to follow the many sudden changes of earth-currents, which accompany the magnetic 

 disturbances. 



Walker has pointed out the importance of having continual photographic records of earth-currents 

 in connection with magnetic records. The matter was taken up by Airy, Astronomer Royal, and earth- 

 current registerings were commenced at Greenwich in 1865, and were continued for two years. UK 

 results are contained in two papers by Airy communicated to the Royal Society in 1868 and 1870; 

 and the conclusions he has drawn from his observations have to a great extent formed the basis oi 

 later discussions. 



(') C. V. WALKEK: Phil. Trans. 1861, p. 89, and 1862, p. 203. 



(2) LAMONT : Der Erdstrom und der Zusammenhang desselben mil dem Magnetismus der Erde, 1862. 



( 3 ) loc. eit., p. 114. 



