670 Prof. F. A. Lindemann on the 



a spherical shell under the influence of their mutual repul- 

 sion and then gradually to leak away. He shows that this 

 would account for the observed magnetic phenomena and 

 possibly for the aurorse. 



There are a number of reasons which show that a rays 

 alone cannot be the true cause of magnetic storms, the main 

 ones being that they cannot be produced on the sun in 

 sufficient quantities, that they cannot proceed as a beam for 

 more than one or two solar diameters on account of the 

 mutual repulsion of the particles, and finally that they could 

 not approach the earth after the first few seconds on account 

 of the charge the earth would rapidly acquire. 



According to Dr. Chapman there should be about 

 4"4.10 - ' a particles per cm. 3 spread in a beam or cone of 

 some 17 J from the sun, i. e. of radius 2'2.10 12 cm. where it 

 crosses the earth's orbit. There does not seem to be any 

 obvious reason why these rays should be confined to such 

 a cone ; on the contrary, a particles from radioactive sub- 

 stances would be distributed initially equally in all directions. 

 Apart from this however, if the velocity of the a particles 

 is 2.10 9 cm. /sec, which corresponds to a range of some 

 6 cm. in air at normal temperature and pressure, this means 

 that about 1'5.10 28 a particles should be emitted per second 

 by the particular disturbed part of the sun's surface. Since 

 it is by no means always large sun-spots which are in 

 question, one may perhaps estimate the area from which the 

 « particles are emitted as 3.10 18 cm. 2 corresponding to a 

 diameter of 2.10 9 cm. Since their range is about 6 cm. 

 in air, they must necessarily proceed from a layer of such 

 thickness that its mass per cm. 2 is less than 8.10 -3 gramme. 

 Therefore less than 2*5. 10 16 grammes should emit 1*5. 10 28 

 a particles per second, i, e. each gramme of substance would 

 emit more than 4.10 -12 gramme per second. The life of 

 the substance would therefore necessarily be less than 

 2*5.10 11 seconds. Since the sun has obviously existed for 

 longer than this, the sole way out is to assume that the 

 substance only becomes radioactive on reaching the sun's 

 surface. This alternative is quite untenable, since it may 

 easily be shown that it would require either a temperature of 

 some 10 9 degrees, or a pressure sufficient to raise the density 

 many thousandfold in order materially to influence radio- 

 active processes. The alternative assumption, that the short- 

 lived substance is produced in the interior and then separated 

 from the parent substance and carried in a concentrated 

 patch to the surface, is too fantastic for serious consideration. 

 If a patch of the sun were to be covered suddenly with 



