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BELL SYSTEM TECHNICAL JOURNAL 



water, as we shall see, is serving not merely as a screen for keeping out 

 the rays of radioactive matter in the earth but as an instrument for 

 studying the penetrative power of the unknown rays themselves. 

 Records, as I just said, were made an hour apart, and ordinarily were 

 continued over two days at each depth. 



Meters 

 32.4 



II 



Hours 

 10 



15 



20 



78.6 



i!if!!il!!!il!!iil!i!!!i!!!!!! 



173.6 



!itoi;:;?^^";;'::;!-;::!''^^N,;,, 



230.8 



i pi:!!i;i;«iiii;i|';'!ii^^^ 



Fig. 2 — Photographic registration of the position of the string of a string electrometer, 

 showing gradual shift due to discharge by cosmic rays (Regener). 



Measurements were made at seven depths: in metres, these amounted 

 to 32.4, 78.6, 105.2, 153.5, 173.6, 186.3, and 230.8. They were plotted 

 as function of depth; the resulting curve, shifted downward by 0.78 (we 

 need not consider the exact meaning of the units along the axis of 

 ordinates) appears as / in Fig. 3. It is concave-upward, of a shape 

 which suggests that there are both a Restgang, and ionizing-rays di- 

 minishing in strength as they descend through the water from above. 

 But it is not sufficiently prolonged to permit the eye to decide with 

 confidence the value of the Restgang; the exact effect of the ionizing 

 rays is therefore not to be judged by inspection. How did Regener 

 proceed? He postulated that the readings y at the three greatest 

 depths (depth measured downward from the surface being denoted by 

 x) are sums of a constant and an exponential term: 



y = A + ^e-"^; X = 173.6, 186.3, 230.8, 

 and found what values must be given to A, B, and m in order to get the 



