COSMIC RADIATION — BLACKETT 



179 



nearly parallel to the lines of equal geomagnetic latitude. They also 

 run nearly parallel to the lines of equal auroral frequency. The 

 explanation of this relation will be mainly left to the next lecture, 

 but can be given shortly by saying that the cosmic rays as they reach 

 the upper levels of the earth's atmosphere are mainly electrically 

 charged particles of very great energy. These particles are deflected 

 by the magnetic field of the earth so as to reach regions of higher 

 latitude more easily than regions near the equator. This behavior is 

 very similar to that of the charged electrical particles which are held 

 to be the origin of the northern lights. In fact, the theory of the 

 aurora polaris, proposed many years ago by Birkeland and Stormer, 



•a 



c 



o 



S 1.7 



30* 



20" 



10° 0° 10' 20" 20 

 Geomagnetic latitude 



Figure 3. 



M' 



. SO 60 

 (Clay) 



applies almost unchanged to cosmic radiation. The intensity of 

 cosmic radiation is found to be nearly constant from latitude 50° 

 north up to the poles, but decreases toward the magnetic equator, 

 the decrease amounting to about 15 percent. Figure 3 shows the 

 results obtained during a voyage from Southampton to Cape Town. 

 At greater heights, the increase from the equator to the poles is much 

 greater. 



This study of the intensity of cosmic radiation at great heights and 

 in different latitudes is of the highest importance, but our knowledge 

 is at present extremely fragmentary and quite inadequate for many 

 purposes. In order to test theories as to the nature and behavior of 



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