The Story of Cosmic Rays 1 



By W. F. G. Swann 



Director, Bartol Research Foundation of The Franklin Institute 



[With 2 plates] 



The atmosphere is, to an extremely small extent, a conductor of 

 electricity, and we know that such a condition results from the presence 

 of charged atoms called ions, with positive and negative charges. 

 These occur in practically equal numbers. The positive ions are those 

 atoms that have lost a negatively charged particle — an electron — and 

 the negative ions are those that have acquired the negative charges lost 

 by other atoms. As a result of mutual attraction, the negative ions are 

 continually returning their negative charges to atoms that have lost 

 such charges, so that if the continued existence of a "state of ioniza- 

 tion" is to be maintained, there must be present some agency that 

 continually detaches electrons from atoms. Such agencies are, in 

 part, the radiations that are emitted by the normal radioactive con- 

 tamination of the atmosphere. However, such agencies are confined to 

 low altitudes, so that to account for ionization at high altitudes, where, 

 indeed, it is greater than at low altitudes, we must invoke some other 

 agency. This agency is the cosmic radiation which, at first, was as- 

 sumed to be a single kind of radiation coming into our atmosphere 

 from above. 



The simple concept of a single type of radiation entering the atmos- 

 phere and being responsible for the phenomena observed had to be 

 modified as time progressed. The situation, as we have it today, is 

 much more complicated. We have been led to believe that there is 

 a "primary radiation" consisting for the most part of positively 

 charged hydrogen atoms, and that the radiation, on entering our 

 atmosphere, bombards the atoms of the atmosphere with the resulting 

 emission of all sorts of other atomic particles which, in their totality, 

 constitute what we observe as the cosmic radiation. 



ATOMS AND ELEMENTARY PARTICLES 



Atoms and their parts. — An atom of matter consists, essentially, 

 of two parts — an inner core, composed of positively charged particles 



1 Reprinted by permission from Sky and Telescope, published at Harvard Col- 

 lege Observatory, Cambridge, Mass. 



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