[king] PE NETRATING RADIATION FROM THE EARTH 101 



gçct^ 3_ — Discussion of Observations on the Gradient of the Penetrating 



Radiation. 



An excellent summary of the present state of knowledge on the 

 subject of the penetrating radiation and an account of the difficulties 

 attending the exact measurement of its intensity has recently been 

 published by A. B. Chauveau.* An account of the attempts to 

 measure the gradient is given in Sect. 18 of the paper just referred to. 

 While it is unnecessary to repeat the summary of the paper quoted 

 it will suffice to state that observations taken from the top of high 

 buildings or other structures have a doubtful value both on account 

 of the unknown radium content of the building material and the prob- 

 ability of a contrilmtion to the penetrating radiation being due to a 

 distribution of active deposit from the atmosphere. On the other 

 hand the results obtained from balloon ascensions have not revealed 

 the required gradient, and as no explanation of the failure has been 

 forthcoming, the writer has ventured to bring forward evidence to 

 show that the results may be vitiated by ionization contributed by 

 radiations from an active deposit on the car of the balloon or even 

 on the electroscope itself. This explanation has already been suggested 

 to explain the variation of Wulf's observation on the Eiffel Tower 

 from the requirements of theory, f 



It is well known that balloons may become very highly charged 

 relatively to the surrounding air. An account of the subject is to be 

 found in the Report of the Advisory Committee of Aeronautics, 1909- 

 1910.Î According to evidence there collected (p. 119) and also to ex- 

 periments and calculations described by G. W. Walker (p. 112) it 

 seems probable that a balloon takes a considerable length of time to 

 attain the potential of the surrounding air. It is probable that in 

 the course of an ascent the balloon may be at a potential of several 

 thousand volts from that of the air in its neighbourhood: definite measure- 

 ments on this point were made by Dieckmann in 1911 during two 

 voyages of a Zeppelin airship.* If this difference of potential should 

 happen to be negative (as in the case of a balloon rising rapidly from a 

 normal negative earth) enough active deposit might be collected on 

 the balloon, its car and fixtures and perhaps even on the electroscope 

 itself to give rise to a penetrating radiation of sufficient intensit}'' to 



*Chauveau, A.B., "L'ionization de l'air en vase clos et la radiation pénétrante, 

 Part I, Le Radium, 10, Jan. 1913, p. 17, Part II, Le Radium, 10 Feb., 1913, p. 69. 



tChauveau, loc. cit., p. 73; Rutherford Radio-activity, 1913, p. 636. 



JPublished by Wyman & Sons, London, 1910; see also abstracts 24, p. 159 and 

 54, p. 180. 



* Dieckmann, M., Zeit. fur Flugtechnik und MotorluftscMfahrt, Jan. 14, 1911; 

 Abstracted in Report of the Advisory Committee for Aeronautics, 1910-11, p. 124. 



