THE NATURE OF THE COSMIC RADIATION^ 



By TuoMAS H. Johnson 

 Assistant Director of the Bartol Research Foundation of The Franklin Insti- 

 tute and Research Associate of the Carnegie Institution of Washington 



[With 4 plates] 

 1. HUMAN VALUE OF COSMIC RAY INVESTIGATIONS 



Scientific research projects divide themselves into two classes ac- 

 cording to the human value of the results; those from which some 

 new device or method develops, augmenting our comforts, conven- 

 iences, or abilities, and those resulting in new points of vieAV, 

 Values of the first type are evident in every phase of practical living. 

 The second are not as generally appreciated, though the values are 

 often more genuine. 



It is not always possible at the outset to know into which class a 

 particular search for the truth will fall. Oftentimes values of both 

 types develop. But in the case of certain astronomical investiga- 

 tions, of which the study of cosmic radiation is typical, the philo- 

 sophic interest is paramount. The total energy falling upon the 

 earth's surface in the form of cosmic radiation is about one-thou- 

 sandth of star light or one-billionth of sun light. Even if the cos- 

 mic ray energy were equal to sun light it would probably be an 

 inferior source of power, for the extreme penetrating ability of the 

 cosmic radiation prevents its concentration for conversion into use- 

 ful forms of work. 



2. METHODS OF INVESTIGATION 



Although the cosmic ray intensity is minute when expressed in 

 terms of total energy, single cosmic rays possess more energy than 

 any other known form of radiation, and they are easily detected, one 

 at a time. If we had suitable nerve responses we would be conscious 

 of about 25 cosmic ray shots through some part of the body each 

 second. The rays may be detected in several ways, all of which 



1 Lecture, Carnegie Institution of Washington, Washington, D. C, Mar. 12, 1935. Re- 

 printed by permission from the Journal of the Franklin Institute, vol. 220, pages 41-67, 

 July 1935. 



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