( 595 ) 
nation, when I pointed out as follows how the Polar Auroras 
originate on the earth through the spots on the sun. *) If we want 
to follow this explanation, we must suppose that there are radio- 
active substances on the sun. This supposition is surely not in the 
least extravagant, since we know how generally such substances are 
found on the earth and also take in consideration, how as a rule 
the same substances which we know on the earth, are also found 
on the sun. Moreover it is probable, also according to Ruruer- 
FORD, that on the sun the radioactivity of matter will show itself 
even more energetically than on the earth, which is so much cooler. *) 
If now there are radioactive substances on the sun — and also the 
presence of Helium is in favour of this — such substances will 
remain hidden under the photospherical shell, owing to their 
great weight, just as all other elements of great weight. So, under 
this shell their a, @ and y rays will originate. But for the greater 
part these rays will be prevented by this comparatively thick shell 
from escaping from the sun. Only where there are holes in this 
photospherical shell and so especially where we see spots, this 
impediment will not be so great. And so, out of each spot just as 
out of the leaden vessel in the investigations of Mrs. Curm a bundle 
of more or less parallel 8 and y rays will come forth, vertically 
going out into the wide world. If now such a bundle, which is often 
many times thicker than the earth, comes in contact with our atmos- 
phere, it will bring here about all these electric and luminescence 
phenomena which have already been considered by BIRKELAND, 
PaurseN and Arruentus 1 as caused by kathode rays of the sun 
and 2 as the cause of our Polar Auroras and of our magnetic 
disturbances. *) 
If, by means of these supposed strong bundles of rays there is 
such a simple connection between these earthly phenomena and the 
cavities of the solar spots, we understand at once: 
1. why these earthly phenomena have the same period of 11 
years as the spots; 
2. why also every year these earthly phenomena show maxima 
1) De Nieuwe Courant 19 Febr. 1907 — Bull. Soc. Astr. de France Juin. 1907 
p. 283 — Essai d'une Explication du Mécanisme de la Périodicité dans le Soleil 
et les Etoiles rouges variables. Verh. Kon. Akademie van Wetenschappen te 
Amsterdam IX. 6 p. 19—21 (1908). 
2) RUTHERFORD : Radioactivity 1904 p. 344 — MAUNDER: Knowledge Nov. 1903 
p. 255. 
8) ARRHENIUS: Lehrb. d. Kosm. Physik. p. 152 — PaursenN: Bull. Soc. Belge 
d’Astr. Oct. 1906 p. 381. See also my Essai of 1908 p. 20—23 referred to above, 
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