720 



blRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 1903. 





The processes whereby such rays were formed we might call radio-activity in an extended sens 

 or electro-radio-activity. 



We have not yet succeeded, however, in spite of continual experiments, in producing a proof that 

 by this extended radio-activity chemical elements might be transformed into one another, or that heat 

 was developed by the disintegration of a cathode, in the same way as when radium is transformed. 

 The last question would acquire a fundamental importance in the problem of the heat-store and longe- 

 vity of the sun and stars. 



139. According to our manner of looking at the matter, every star in the universe would be 

 seat and field of activity of electric forces of a strength that no one could imagine. 



We have no certain opinion (') as to how the assumed enormous electric currents with enorrtv 

 tension are produced, but it is certainly not in accordance with the principles we employ in technics 

 on the earth at the present time. One may well believe, however, that a knowledge in the future of 

 electrotechnics of the heavens would be of great practical value to our electrical engineers. 



It seems to be a natural consequence of our points of view to assume that the whole of space is 

 filled with electrons and flying electric ions of all kinds. We have assumed that each stellar system 

 evolutions throws off electric corpuscles into space. It does not seem unreasonable therefore to think that 

 the greater part of the material masses in the universe is found, not in the solar systems or nebula?, but 

 in "empty" space. 



Let us see how thickly we should have to imagine iron atoms, for instance, distributed in spa 

 between the sun and the nearest star, a Centauri, if, in a sphere with the distance 4.4 light-years as 

 dius we assumed a mass equal to that of our solar system to be evenly distributed. 



The mass of our solar system may be estimated at 2 X io 33 grammes (see Young, General Astn 

 nomy, pp. 97 and 603). The distance to a Centauri is 4 X io 18 centimetres, and the volume of the said 

 sphere about the sun would thus be 2.7 X io 50 cubic centimetres. 



If the mass of our solar system be distributed over this sphere, there will be 7.5 X io - 4 grammes 

 per cubic centimetre. 



If the mass of an iron atom be put at 5.6 X io - 3 grammes, we find that there will fall i iron atom 

 upon every 8 cubic centimetres of the sphere in question. 



It seems as if no known facts can prevent us from assuming by hypothesis that the average den- 

 sity of these flying ions and uncharged atoms and molecules might very well be, for instance, 100 times 

 greater than that found above. 



The electron theory assumes that the ponderable atoms are surrounded by some bound electrons 

 which oscillate about certain positions of equilibrium and with definite periods. These atoms or ions 

 cannot then, considered optically, have properties that are very different from the optical properties in 

 a dielectric medium. 



Let us therefore imagine that we have on an average io iron atoms per cubic centimetre in empty 

 space, and try to form some idea as to whether such a density would be at variance with the optical 

 properties of space, and in the next place whether this density would be irreconcilable with the assump- 

 tion that the sun sends cathode-rays down to the earth. 



The latter question seems the easier to decide when we consider that there must be a row o 

 ^-r- cubic centimetres, one after another, to contain one gramme of iron. A column such as that wouli 

 be traversed by light in 1900 years. If we assume that the stiff helio-cathode rays of which we are now 



(') See "Sur la Source de 1'eleclricite des etoiles", C. R. Dec. 23, 1912. 



