NEW RESULTS ON COSISIIC RAYS 



Bv R. A. MiLMKAN and G. H. Camkron 



[With one plate] 



The cosmic radiation is defined as that small portion of the " pene- 

 trating radiation " which is of cosmic origin. The main purpose of 

 this paper is to present a preliminary report upon some very recent 

 work which throws new light upon the properties of these extraor- 

 dinary rays, and shows that still harder ones exist than had hereto- 

 fore been found, rays capable of penetrating 190 feet of water, or 

 about 16.7 feet (5 meters) of lead, before being completely absorbed. 



Since doubts have been expressed as late as last summer by some 

 of the foremost of living physicists as to whether or not there are 

 any rays which have as yet been definitely proved to be of cosmic 

 origin, and since up to this moment different observers of undoubted 

 credentials, such as Swann," Hoffmann,^ Kolhorster, and ourselves 

 differ in some cases as much as eight or ten fold in our estimates of 

 the intensity of the cosmic radiation if it exists, our first task will 

 be to present very briefly the nature of the evidence up to the time of 

 these experiments and then to see how the new results supplement 

 this evidence. 



This procedure will have the further advantage of presenting a 

 very beautiful illustration of the slow, step-by-step process by which 

 most advances in science are made, each experimenter building on 

 tlie past, but pushing on, if he is fortunate, a little beyond where his 

 predecessors had gone, until presently the world finds itself in the 

 full glory of a new conception of nature without having been con- 



^ This article is mado up from several recent papers by the authors; the first part, 

 clown to page 222, bcinjr the substance of an eveninc discourse, with additions, delivered 

 b.v Professor Millikan at Leeds, on Sept. 2, 1027, during the nieetin); of the British Asso- 

 ciation, is reprinted b.y permission from the Supplemont to Nature, No. 30.36, Jan. 7, 1028. 



'Swann, Phys. I!ev. (20, .'572; 1027), finds thi' ioiiiz.ition due to such rays on the summit 

 of Pikes Peak to be 0.7.'5 per c. c. per sec. per atnio.'<ph<re, whili^ we found them in the 

 same place to be close to t\ ions. 



■■'Hoffmann, Ann. dor I'hysik (82, 41.3; 1027), finds the ionization at sea level 0.20 per 

 c. c. per sec. on the assumption, taken from Kolhilrster's 102(5 findings (Zeit. f. Physik, 

 ".'■>, 117 ; l!t2ri),that the absorption coefiicient is invariant and of value m1IjO=22X10' cm.->. 

 We, on tbf oilier hand ( I'liys. Kev.. 2S, S.'".l ; 1020), found the absorption coiflicient 

 definitely variable (the rays therefore inhomogeneous), and the ionization at lea level 

 1.4 ions. 



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