BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 1903. 



: 



Now we know that of the 120000 nebulae scattered over the sky, at least half are of a spiral 

 form. The most remarkable thing about them is that there are very often two spirals issuing symme- 

 trically from two diametrically opposite parts of the nebula. 



We have previously seen how the continuous discharges round the magnetic cathode-globe in our 

 experiments, could assume a shape that recalled Saturn's ring. These continuous discharges round the 

 globe may, however, with higher gas-pressure in the almost exhausted vessel, take the form of two 

 spirals, curved in the plane of the equator, issuing symmetrically from two diametrically opposite point? 

 on the globe. 



The accompanying figure (fig. 262) represents an experiment such as this with two such spirals. 

 The photograph was obtained by accident, and I have seen still more interesting pictures appear, severa 

 of which I shall publish at some future time. 



In the above-named work of Poincart, a number of older cosmogonic theories, almost all of whir] 

 are founded upon purely mechanical conceptions, are compared. Those of LAPLACE, LIGONDES and 

 ARRHENIUS are of special interest. In the last-named, the so-called light-pressure plays a conspiciiou 

 part side by side with the force of gravitation. 



In Poincar^'s work, all theories are in turn subjected to kindly criticism, with demonstration of t 



difficulties to which each one leads. It seems to be the celebrated 4 

 Laplace's nebular theory that is still considered to be the strongest. 



Let us now look a little more closely at the idea here put forward 

 namely, that the sun each day emits by electric evaporation or disintegra 

 tion considerable quantities of matter in the plane of its equator whicl 

 forms the part of the electric ring already mentioned, and that in earlie 

 ages this emission of matter has been still greater. 



It is not necessary to admit at first the original nebula extended t' 

 the orbit of Neptune, as the matter is radiated by electric forces outsidi 

 the system at its equator. It is very probable, moreover, that the greate 

 part of the matter thus radiated leaves the system, and in any case take 

 no part in the formation of the planets. 



Our analysis will show that particles from the central body may be so ejected that they afterward 

 move in approximately circular paths near those in which the centrifugal force due to the revolutioi 

 movement counterbalances the attraction of gravitation ; and one could naturally believe that it is jus 

 these globules which condense and form large spheres. 



Our explanation will be applicable, not only to the planets round the sun, but also to all satellite> 

 round the planets. One can imagine Saturn's moons, and Jupiter's, down to the outermost, newly 

 discovered ones that move round the planet in the opposite direction to the inner, originating in a 

 natural manner from matter, which, under the action of an electro-magnetic directing force, has been 

 ejected from the planets in the plane of the equator. 



Looked at in this way, Saturn may still be engaged in making moons by electric radiation. Mimas. 

 almost touching the circumference of the rings, is perhaps the youngest of the satellites. 



132. The equations of motion for an electrically charged particle that is in the plane of the equator 

 of a magnetic globe (.T, y plane), and is moreover influenced by the gravitation of the globe, are 



Fig. 262. 



(I) 



d-y 



r 8 dt 



'tMitx 

 ^ dt 



