THE STORY OF COSMIC RATS — SWANN 265 



tides in the vicinity of the changing magnetic field, they will be 

 whirled around by the electromagnetic forces even though they do 

 not form part of a material circuit. It seems that cosmic-ray ener- 

 gies can readily be acquired by processes of this kind. 



Recently, the foregoing mechanism has been extended to galaxies, 

 where magnetic fields of the order of 7X10 -6 gauss are recognized as 

 existing. On the supposition that these magnetic fields have grown 

 from zero, it appears that a charged particle that had zero energy 

 when the field was zero would acquire energy continually, and could 

 attain an energy greater than 10 19 electron volts by the time the field 

 had risen to 7X10 -6 gauss. The complete story of the possibilities in 

 this matter involves the lifetime of a cosmic ray, and the conditions 

 pertaining to the case where the magnetic field has already attained a 

 finite value at the time the particle, as a result of becoming charged, 

 starts to acquire energy. 



It is also known that if an electrical conductor in a magnetic field 

 is removed from the field, the conductor will tend to carry the mag- 

 netic field with it. What really happens is that the change of magnetic 

 flux that would occur in the conductor, if it simply left the magnetic 

 field behind, introduces electromotive forces and so current. This 

 forms a new magnetic field which just replaces the loss of magnetic 

 flux that would otherwise have resulted from the departure of the 

 conductor from the original field. A. Unsold has called attention to 

 the fact that, in those huge solar cataclysms in which a mass of matter 

 is seen to be hurled from one portion of the sun's surface and to fall 

 back upon another, we have a condition favorable for changing mag- 

 netic fields. If such a mass of matter is conducting and starts from a 

 place where there is a magnetic field, it will pursue its course in the 

 cataclysm, carrying the magnetic field with it until it eventally 

 splashes once more into the sun, resulting in the annihilation or the 

 dispersal of the magnetic field that it carried. The rapid change in 

 magnetic flux through the regions of space in which the cataclysm 

 occurs provides for the birth of electrical forces that can give cosmic- 

 ray energies to charged particles. 



Another method of accelerating charged particles has been sug- 

 gested by D. H. Menzel and W. W. Salisbury and has been further 

 developed by E. M. McMillan. It depends upon energy that is elec- 

 tromagnetic in nature, but with very low frequencies of only a few 

 cycles per second and existing only in the extreme outer portion of the 

 solar corona. Such low-frequency waves may arise from large mag- 

 netic disturbances initiated by solar flares and propagated through the 

 corona. Sparsely distributed ions in the space around the sun (and 

 other flare-type stars) might be accelerated to cosmic-ray energies if 

 a mechanism of this kind actually exists. 



