jam 



668 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 1903. 



that the sun's nucleus received a positive charge, of which, it must be imagined, it would to some extent 

 gradually get rid in the interval between two outbreaks of sun-spots. 



There is one circumstance that is perhaps in favour of this assumption, as also of the first, and 

 that is the peculiar capacity that the sun, in analogy with our magnetic globe, must have. It seems as 

 if an electric condensation must take place, so that the opposed masses of electricity are found as coatings 

 lying close to one another. 



The third assumption seems the most natural when the matter as a whole, is looked at from the 

 point of view of the experimental analogies. It is then a question of the manner in which this net;,- 1 

 charge on the surface of the sun has been produced in interaction with space. If to the negative 

 of electricity on the external surface of the sun, there are to some extent corresponding masses of | 

 live electricity in the interior of the sun, the first and third assumptions may be combined, which again 

 would allow of the mysterious movements of the sun spots in the various latitudes being explained 

 an electromagnetic action. 



It must moreover be admitted, even in the third case only, that a magnetic influence on the in 

 ment of the sun-spots was to be expected, if, as has here been done, the arrangement of the sun-spots in 

 parallel rows, one on each side of the equator, is assumed to be the effect of the magnetic condii 

 The question then is whether it is possible, by an estimate, to show the probability of an explan 

 of the actual motion of the spots in the third case as well only as a magnetic influence. This ap[ 

 to be difficult. It is true that the pencils of cathode rays that radiate from sun-spots in higher latitude 

 curve rapidly down towards the equator, thereby causing the component of the magnetic force at right 

 angles to the current-element to be comparatively much greater in the third case than assumed ir 

 first; but whether this can cause the magnetic retrograde motion eventually produced to be more marked 

 in the case of sun-spots in higher latitudes, than in that of spots in lower latitudes, is doubtful. The distri- 

 bution of the sun's magnetism may perhaps be rather different from what we assumed in the first 

 and thus a fairly good explanation could be given. At any rate, the rotation of the sun's body itself must 

 be greater than the apparent rotation of any sun-spot, and this really agrees with the actual circumstances 



SPOERER'S discovery that groups of sun-spots are inclined to be drawn out in length in a din 

 along a parallel circle on the sun, so that the spots appearing last come to the west of those already 

 in existence, speaks most in favour of a combination of the first and third assumptions. 



The same may be said of SECCHI'S discovery with regard to the characteristic leaps in the normal 

 rotation of a sun-spot, as the leaps usually take place in the direction of the rotation. 



It is at present not easy to see how a negative tension should be continually created by the sun 

 in relation to space. 



It is of course possible to imagine that a surplus of positive ions is always being carried away 

 from the sun or that negative ions are always being carried towards the sun, and that the negative 

 tension is produced in this manner; and that the balance is maintained to some extent by distinct dis- 

 ruptive discharges, as we have presupposed. 



It seems a natural thing, however, to connect the creation of this tension with the sun's radiatior 

 of light and heat. But as MAXWELL'S electro-magnetic light theory at present stands, there is no dired 

 opportunity of assuming that light-energy is carried over into electric energy, and that for that reasoi 

 the rays of light are absorbed into space. 



It is thought by several that Maxwell's equations require a correcting term. Such a term would 

 perhaps have influence just when there was question of a disturbance that spread into infinite space. 



RIEMANN'S discoveries in the transition from infinitely small to finite amplitudes in sound-waves, 

 might possibly afford some information. 



