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BELL SYSTEM TECHNICAL JOURNAL 



energies, the others (those of which the paths are uncurved) either have 

 yet more enormous energies or else are neutral. These facts make it 

 impossible to suppose that photons are the immediate agents. Before 

 continuing with the deductions we will consider the third method. 



The third method of studying cosmic rays involves the use of a 

 "Geiger counter" or some modification thereof- — a metal-walled gas- 

 filled tube with a needle or (more commonly) a wire mounted inside it 

 and insulated from the wall, which is connected to one pole of a battery, 

 the needle or wire to the other. If the tube is properly designed and 

 treated, the E.M.F. of the battery properly chosen (this seems to re- 

 quire a lot of experience) the passage of an ionizing particle across the 

 gas between needle and wall is likely to evoke a sudden and violent and 

 very short-lived current-flow. If a telephone-receiver is in the circuit, 

 there is an audible click; if a galvanometer or electrometer is used with 

 an optical device for recording its deflections upon a moving film, there 

 will be a photographic trace of the discharge. 



In experiments on cosmic rays with this device, it is the custom to 

 employ a pair of counting-tubes (or even three) and to accept as valid 

 data only the discharges which occur in either simultaneously with 



Fig. 12 — Apparatus of Bothe and Kolhorster for counting ionizing particles and 

 estimating the absorption thereof in metals. 



discharges in the other. I illustrate the method by a sketch from the 

 work of Bothe and Kolhorster (Fig. 12) in which on the right one sees 

 the two counters in longitudinal section, on the left one sees them in 

 cross-section as they lie within their heavy armoring of metal. 



