382 



Sir E. Rutherford and Mr. A. B. Wood 



Oil 



path taken by some o£ the rays through the mica on account 

 of the nearness of the source and screen. Calculations 

 showed that the influence of obliquity could only account for 

 a small fraction of the difference actually observed. 



Fijr. 3. 



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4- 6 



Range in cms. 



10 



The results we have so far obtained certainly seem to 

 indicate either that (1) the long-range alpha particles are 

 expelled with variable velocities over a comparatively narrow 

 range, and in this respect differ markedly from alpha particles 

 from ordinary radioactive products which are known to be 

 expelled with identical velocity, or (2) that two homogeneous, 

 groups of alpha rays of characteristic ranges are present. In 

 order to distinguish definitely between these two hypotheses, 

 it would be necessary to count many thousands of alpha 

 particles, but other evidence suggests that (2) is the more 

 probable explanation. 



The slope AB ends at about a range 10'2 cm. and when 

 the number of alpha particles is reduced to about two-thirds 



