PART. II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. V. 613 



I now assume that these corpuscle-currents, which are continuously given out and probably most 

 strongly from the neighbourhood of the sun's equator, are somewhat less stiff as regards magnetism than 

 the rays which come in eruptions from the portions in greatest activity around the sun-spots. The 

 constant rays are thus less penetrative through matter, and come probably from lesser depths in the 

 atmosphere of the sun. 



I have recently in a note(') in C. R. de 1' Academic des Sciences, Paris, in explanation of certain 

 phenomena in the magnetic storms, advanced the opinion that the sun is magnetic, with a magnetic 

 moment of the order io 2s or about 150 times as great as that of the earth. 



If this is the case, the corpuscles which are constantly given out will principally issue both from 

 the regions near the magnetic poles of the sun, and moreover the rays will to a very great extent be 

 concentrated and form a ring in the plane of the sun's magnetic equator, which probably only forms a 

 small angle, or is perhaps identical, with the heliographic equator. 



There is no reason, as we shall see further on, to suppose that the sun's magnetic axis should 

 not be identical with the axis of rotation, as there can hardly be magnetisable masses with permanently 

 fixed positions in the sun. 



In the plane of the sun's magnetic equator the corpuscle-rays will doubtless, as an elementary study 

 shows, bend comparatively sharply, near the sun; but they will keep constantly in the plane. 



This question, the examination of how the corpuscle-rays move in the magnetic equator of a mag- 

 netic globe, I have investigated experimentally and have obtained very successful results. See fig. 223. 



By allowing a smooth magnetic sphere (without phosphorescent coating) to be the cathode in a 

 discharge-container, a wonderfully developed luminous ring is easily obtained around the globe. 



The photographs here reproduced have been taken with a magnetic ball of 8 cm. in diameter in the 

 smallest of the prismatic discharge-containers. It was seen that the ring expanded immensely with the 

 stiffness of the rays and with the magnetic globe's magnetic momentum. I was unable in this instance 

 to attain a difference in the tension between anode and cathode of more than 700 volts, when the 

 brass ball was the negative pole; but even at this tension and a magnetising current of 21 amperes 

 from an isolated storage battery the ring became so large that it at times reached to the glass 

 walls of the container. I shall repeat the experiment with my largest discharge-box, when I get it 

 repaired again, for I am convinced that I shall be able to obtain a perfectly flat ring of light of 30 cm. 

 diameter around my strongest magnetic globe No. 7, which is also of 8 cm. diameter. 



If I were in possession of sufficient quantities of pure radium-bromide, I would coat the equatorial 

 portions of my strongest magnetic globe with that substance. It would be of interest to see if rings of 

 (i and a rays could then be made visible. 



I will here observe, that when I have on previous occasions produced a luminous ring round my 

 terrella by cathode rays from a somewhat distant cathode, it is possible that I have been mistaken. It 

 may be that the magnetic ball has been sufficiently negative compared with the surroundings for an 

 emanation of negative rays to take place at the same time as the ball is illuminated and surrounded by 

 cathode rays from the real cathode. There are two reasons for this. In the first place, it was, as 

 already mentioned, only under quite exceptional circumstances that the ring was formerly produced, while 

 it is now produced in the way here described never wanting, and in the second, the difference in the 

 tension need only be very small before the negative radiation from the ball occurs, so that such 

 a difference in tension can very easily have taken place in the course of the earlier experiments. 



But this condition does not, of course, affect our previous main results, in which, by the aid of 

 various screens, we have proved how, amongst other things, rays from the cathode circulate around the 

 terrella, bending above and beneath the plane of the magnetic equator. 



(') C. R. 24 Jan. 1910. 



Birkeland. The Norwegian Aurora Polaris Expedition, 1902 1903. 78 



