260 



ANNUAL REPORT SMITHSONIAN INSTITUTION, 195 6 



On the other hand, observations of the solar field at one time do not 

 necessarily guarantee its value at another. This warning is important, 

 for some stars are known with certainty to possess variable magnetic 

 fields. H. W. Babcock found in 1948 that the star HD 125248 has a 

 magnetic field of 6,000 gauss at its pole, a field that reverses itself to 

 a comparable value of opposite sign in a period of about 10 days. In 

 Sky and Telescope for March 1950, Otto Struve presented a detailed 

 discussion of "Stars as Magnets." 



10O- 



•- 9.0- 



B-29 Flights 



1946 



Counting Rate vs. Latitude 

 33,000 Feet 



10 20 30 40 



geomagnetic latitude 



60 

 N 



Figure 6. — How cosmic-ray intensity varies with latitude is shown by these measurements 

 made under the author's direction in 1946 with airborne Geiger counter trains. As the 

 number of counts per minute varies, each measured intensity has a statistical uncertainty, 

 indicated by the length of the vertical line representing it. Note the leveling off of the 

 curve at about 50° latitude. 



Finally, in connection with cosmic magnetic fields, it has been sug- 

 gested that the great galaxies of space may be the seats of magnetic 

 fields. The magnetic fields in question are extremely small, of the 

 order of 10~ 5 gauss, but their great extent makes them potent influences 

 on the paths of the cosmic rays within the galaxy. Theoretical con- 

 siderations show that a charged particle coming to the boundaries 

 of such a region would be turned back into the galaxy as though the 

 latter were provided with a reflecting wall, and similar considerations 

 operate to prevent any cosmic ray that is outside the galaxy from enter- 

 ing it. Thus, on such an assumption, the cosmic rays within the galaxy 

 would remain imprisoned within it forever or until destruction 

 through collision with atoms or with other material in the galaxy, such 

 as the stars, terminated their existence. 



THE ORIGIN OF THE PRIMARY COSMIC RADIATION 

 Early students of the primary cosmic radiation pictured it as dis- 

 tributed with equal intensity over the whole of galactic and inter- 

 galactic space. Such an idea is attended with considerable difficulty. 



