266 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1956 



But if the general cosmic radiation originates in stellar flares, why 

 does it come nearly uniformly from all directions? This difficulty 

 attends any theory that involves the stars as the origin of cosmic rays. 

 Therefore, it has become customary to postulate an extensive mag- 

 netic field extending throughout the whole galaxy. This field is 

 supposed to be weak but sufficiently extensive to curl up the paths of 

 the cosmic-ray particles in such fashion as to prevent their escape 

 from the galaxy, and at the same time to provide, as the result of 

 successive reflections at the boundaries of the galaxy, for a condition 

 in which an observer on our earth, for example, receives rays with 

 approximately equal intensity from all directions. 



If cosmic rays are purely stellar in origin, however, we might expect 

 cosmic radiation from the sun to outweigh that from the other stars 

 by something like the extent to which sunlight exceeds starlight. This 

 is not the case, and radio noise from the stars in general seems to out- 

 weigh that from our sun ; therefore, Unsold is driven to assume that 

 the sun is not typical in these matters and that the cosmic-ray activity 

 of many stars may be very much larger than that of the sun. 



An alternative not inconsistent with the possibilities is to attribute 

 practically the whole observed cosmic radiation to the sun itself. For 

 this, the magnetic field of the space around the sun would have to con- 

 fine cosmic rays to the general vicinity of the solar system, with bound- 

 ary reflections producing the observed near-uniformity from all di- 

 rections. It is a fact that unusual solar activity is accompanied by 

 variations in measured cosmic radiation. Thus, for example, in July 

 of 1946 an exceptionally large flare developed on the sun, and during 

 this period a change of as much as 20 percent in cosmic-ray intensity 

 was observed by stations of the Carnegie Institution of Washington 

 distributed in various localities. 



Abundances of the elements. — Suppose that, regardless of the 

 methods of origin and places of origin of the rays, different substances 

 contributed to the rays in proportion to the amounts of the substances 

 present. If the rays came directly to us from their places of origin, 

 the proportions of atoms of different kinds in the primary rays should 

 reflect the abundances of the different kinds of atoms in the universe. 



If, however, the rays are confined by the boundaries of a magnetic 

 field co-extensive with the galaxy, like fish kept in a gigantic pool, 

 they will increase in numbers without limit. But each fish will die 

 eventually, and a state of equilibrium will finally be reached in which 

 the density of fish is such that the number that die per year will equal 

 the number thrown into the pool. For a given rate of supply to the 

 pool, the ultimate density will be greater, the greater the life of the 

 fish. If fish of different kinds have different lives, their ultimate rela- 

 tive numbers will reflect their relative lifetimes as well as the rate at 

 which they are thrown into the pool. 



