Atmosphere due to Radioactive Matter. 39 



The results shown in the table (18) are very remarkable. 

 They indicate a decrea-e of ionization with altitude which is 

 within the limits of detection for an elevation o£ 100 metres. 

 They show, moreover, that at 1000 metres altitude the pene- 

 trating rays from the earth are ineffective as an ionizer. This 

 result cannot well be put to the proof by ascending a mountain, 

 because the radium contents of the ground beneath the 

 observer are changing as he ascends. The experiment may 

 be commended to those who are able to fly kites or captive 

 balloons for 24 hours at a few hundred metres. Jt would 

 be necessary to have an electroscope with a low natural 

 leak and insulation of a high order fortified with a guard 

 ring. Gockel has made observations in a balloon (not 

 captive) at an altitude of 4000 metres on the penetrating- 

 radiation and found but a moderate decrease in the saturation 

 current of an electroscope, carried upwards in the balloon. 

 There are, as he points out, difficulties and uncertainties in 

 making such measurements. 



It will be seen from this paper that the radioactive theory 

 of the ionization of the atmosphere is gradually approaching 

 what may almost be termed an exact science, but that there 

 are three outstanding problems of difficulty and importance. 

 These are: (1) the high value of the ionization over the ocean 

 is not yet explained (n is larger than expected, q is unknown) ; 

 (2) the rapid decrease of ionization with altitude has not 

 been detected ; (3) the theoretical value of the ionization due 

 to the penetrating radiation is less than that found when 

 observers completely screen an electroscope with lead. 



Until these three questions have been satisfactorily ex- 

 plored we cannot rest wholly content with the theory, but 

 have a vague feeling that all matter may give rise to feeble 

 rays of the Rontgen type, of which the more penetrating 

 may integrate into an effective total. This last view is by 

 no means advocated by the writer. 



Last May I attempted some measurements on the North 

 Atlantic, and found that in a cabin of the iron s.s. ' Dominion/ 

 in mid-Atlantic, the leaf of an electroscope closed a little 

 more slowly than on land, indicating a slight decrease of 

 penetrating radiation over the ocean. But I regret to add 

 that the inherent difficulties of observations on shipboard 

 prevented me from reaching any exact or convincing 

 results. 



The writer will be grateful for any information or sug- 

 gestions tending to correct the somewhat tentative values 

 given in this paper. 



July 1910. 



