182 BELL SYSTEM TECHNICAL JOURNAL 



increases. True, the theories are based on the assumption that the 

 energy of the ionizing particles is derived from the photons: if some of 

 them originate from disintegrated atom-nuclei, as the seeming presence 

 of protons among them suggests, the energy of these may be greater 

 than that of the primary photon itself. 



Could we dispense altogether with the notion of a beam of electro- 

 magnetic waves coming from above, and imagine that there are no 

 cosmic rays other than these fast-flying particles, which then must be 

 supposed to come down into the lower atmosphere from above? This 

 possibility cannot be dismissed; against it, however, speaks the strong 

 testimony of several observers who have travelled far and wide in the 

 search for indications that the intensity of the rays varies from point 

 to point on the surface of the earth. For the earth is a magnet; and 

 while the strength of its field is minute compared with that prevailing 

 within a few inches of an electromagnet or even an ordinary horseshoe 

 magnet, the extent thereof is so great that electrons or protons coming 

 up to our planet from interstellar space are liable to be enormously 

 deflected. Charged particles of energy- values such as I have been 

 mentioning (millions or tens of millions of equivalent volts) should 

 reach the earth prevailingly in the region of the magnetic poles, if 

 they start uniformly from all directions. Now, Bothe and Kolhorster 

 took their instruments — three electroscopes and a pair of counting- 

 tubes — on a cruise through Arctic waters; the ship started from Ham- 

 burg and returned there, its course encircling Iceland and passing 

 close to Spitzbergen; there was no sign of a systematic variation of 

 the readings. Millikan, whose data in California had agreed with his 

 data in Bolivia in the admirable way which Fig. 4 displays, made a 

 still finer test: in the summer of 1930 he went "to the settlement which 

 is much the nearest to the earth's north magnetic pole of any settlement 

 on earth, namely, Churchill, 750 miles due south of the pole on the 

 west side of Hudson's Bay — ^at present a construction camp. . . . 

 The mean results, when compared with those similarly taken at 

 Pasadena during the last week in July and the first in August, show 

 that the cosmic rays have precisely the same intensity at Churchill, in 

 latitude 59, as at Pasadena in latitude 34, the mean results in the two 

 places being 28.31 ions per cc. per sec. and 28.30 ions per cc. per sec. 

 respectively, as measured in my particular electroscope. I think the 

 error in these measurements cannot possibly be as much as 1 per cent." 

 A British expedition to the Antarctic made measurements of cosmic 

 rays within 250 miles of the south magnetic pole, and found the same 

 intensity there as in Australia.^** It is difficult to doubt that anything 



20 K. Grant, Nature, 127, 924 (1931). 



