COSMIC RADIATION — JOHNSON 213 



Having identified a component which is probably electronic and 

 whose properties are different from those of the unbalanced positive 

 component, the only remaining possibility for the latter is the pro- 

 ton, the nucleus of the hydrogen atom. 



11. THE SOURCE OF THE COSMIC RADIATION 



The existence of an intense unbalanced positive component sug- 

 gests that we look for electric fields as the source of cosmic-ray 

 energies. Accustomed as we are to electrical displays during thun- 

 derstorms and volcanic eruptions, it is easy to imagine similar proc- 

 esses taking place on stars. Negatively charged clouds of dust or 

 condensed vapor, high above the surface of a star could draw out 

 positively charged atomic ions from its surface or upper atmosphere 

 and project them, like the beam of a cathode-ray tube, into cosmic 

 space. Nuclei of helium and hydrogen atoms, the principal con- 

 stituents of the stellar atmosphere, would thus become the cosmic 

 rays. During their passage through interstellar space these rays 

 would encounter small quantities of matter and secondary rays 

 would be generated. The secondaries could constitute the positive 

 and negative electron component of what appears to us to be the 

 primary radiation. If the picture is correct, one would also expect 

 to find photons which would have been generated in a similar way 

 in the interstellar spaces. 



The secondary hypothesis of the origin of the balanced electron 

 component raises the possibility of using its intensity as a measure 

 of the total amount of matter in the space which the rays have trav- 

 ersed from their point of origin. Experience regarding generation 

 of secondary cosmic rays requires the choice of 10 grams per cm^ 

 as a lower limit for the amount of matter within which an observable 

 electron component could be produced. This lower limit of mat- 

 ter can be translated into a lower limit of distance from the source 

 for the change in color of distant stars gives a means of estimating 

 the density of matter in interstellar space. Using Becker's esti- 

 mate of 0.4 X 10"^*^ grams per cc, it results that distances of the order 

 of from 1 to 10 billion light-years would have to be traversed before 

 the requisite amount of material could be encountered. It is inter- 

 esting that these figures are of the order of the diameter of the ex- 

 panding universe as deduced from the red shift and are consistent 

 with the idea that our principal sources of cosmic radiation are the 

 extragalactic nebulae which are uniformly distributed throughout 

 space. 



Such speculations would lead to the conclusion that cosmic rays 

 are of the same intensity throughout intergalactic space as here 

 within our galaxy, and if this is the case, the total energy in the 



