314 



BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 1903. 



We will now imagine this amount of energy radiating from a sun-spot, and that the bundle of rays 

 is so large that the conditions, so far as the earth is concerned, are the same as if corpuscles were being 

 steadily emitted from the entire surface of the sun. We may mention that farther on, when explaining 

 other terrestrial-magnetic phenomena, we shall assume that corpuscles do continually radiate from the 

 whole of the sun's surface ; but they must be assumed to possess properties somewhat different to those 

 of the corpuscles that radiate from the sun-spots. 



In our calculation we shall employ the same value for the earth's radius as in Article 36, namely 

 6366 kilometres, the radius of the earth's orbit is taken as 23,440 times that of the earth, and the radius 

 of the sun as 109 times that of the earth. The amount of energy that is emitted per square centimetre 

 from the sun's surface in the form of rays will then be 



10 



It 



7.36 X io 9 = 2.7 X io 9 ergs per second. 



it 63652 io 10 iog : 

 If we keep the same designations as before, we thus obtain 



Nf.iv* = 2.j X io 9 , 

 in which, employing the same ft rays as before, we have the following values: 



,U = 1.2 X IO-* 7 (!) 



v = 2-. 59 X io 10 . 



Hence we find that 



N = 6.7 X io 1 ", 



which is the number of ft particles that each square centimetre of the surface of the sun-spot would 

 per second. 



Now i gramme of radium emits 7.3 X io 10 ft particles per second, and at the same time gives ofl 



100 

 3600 



gramme-calories ( 2 



We then obtain 



6.7 X io lr ' 100 



7.3 X io 10 3600 



gr. calories, answering to about 14 h.-p., 



which is thus the amount of energy that is set free by a disintegration of the sun's matter, which would 

 answer to the quantity of rays emitted from it in the form of these corpuscular rays. 



This amount corresponds, as already stated, to the amount of energy which the sun sends out ir 

 the form of light and heat. If the solar constant equals 3, we find a radiation from every square centi- 

 metre of the sun's surface of about 13 horse-power. 



A disintegration such as this in the sun does not necessarily presuppose the presence there of 

 great quantities of radium, uranium, or thorium. 



Rutherford, in his work entitled "Radio-Activity" ( 3 ), says : 



"There seems to be every reason to suppose that the atomic energy of all the elements is of a 

 similar high order of magnitude. With the exception of their high atomic weights the radio-elements 

 do not possess any special chemical characteristics which differentiate them from the inactive elements. 

 The existence of a latent store of energy in the atoms is a necessary consequence of the modern view 



I 1 ) See Sir J. J. Thomson's "Corpuscular Theory of Matter", pp. 16 & 33 London, 1907. 

 f 2 ) See E. Rutherford's "Radio-Activity", 2nd edition, pp. 436 & 474 Cambridge, 1905. 

 ( 8 ) I. c., p. 475. 



