l8 KR. BIRKELAND. M.-N. Kl. 



According to Arrhemus this production is at present about 400 

 millions of tons per annum upon the land-surface of the earth and is 

 chiefly produced by lightening. 



If then at any time the permanent ray-disc round the sun constantly 

 contained rays of such a stiffness that Hç ^ 10' C. G. S. and of such 

 density as in our present strong polar precipitation, the bulk of rays in 

 the ray-current would pass over the earth at a height of perhaps 100 km. 

 A very great mass of rays would then go still deeper down and produce 

 the most brilliant auroral phenomena of hitherto unknown intensity, and 

 the highest layers of the atmosphere would assume an overwhelming tem- 

 perature every day, but only on the evening and night side of the earth 

 with the maximum of effect a little after midnight. 



It is in this way possible to account for the warm climate of the 

 polar regions during the earl}' Tertiär}' period. Even the fact that the 

 contemporaneous vegetation of Japan pointed to a considerably cooler 

 temperature than exists to day can be explained, as Japan lies near the 

 magnetic equator and thus could not profit by the corpuscular energy. 

 And the ordinary insolation from the sun may have been less than to- 

 day, for much light and heat is even today absorbed in the »dusky veil« 

 round the sun, which I believe stands in intimate connection with the solar 

 corpuscular emanation. Se »A. P.« p. 670. 



If we thus admit an enormous density of the ray-disc round the sun, 

 it is at the same time almost ascertained that the ordinary insolation will 

 be very much diminished by absorption and scattering. 



Let us now try to go a step further. 



After the sub-tropical climate in northern and central Europe a general 

 lowering of temperature took place and the »Great Ice Age'< followed 

 with a great advance of thick masses of ice from North Polar areas to low 

 latitudes. It is claimed by many investigators of the glacial epoch that 

 there is evidence of repeated advance and recession of the glaciers or 

 ice-sheets, which are usually attributed to alternate phases of severe and 

 mild climate. The American deposits are thought to furnish evidence of 

 six distinct periods of advance separated by the recession of the ice and 

 the growth of vegetation on the area vacated by it. 



It is stated that some of these interglacial stages must have been of 

 considerable duration, probably greater than the interval between the last 

 retreat of the ice and the present day. It is considered also that the 

 vegetation of the interglacial stages indicates a mild climate, in some cases 

 not differing sensibly from that of the present day. 



