702 



Prof. E. Rutherford and Dr. H. Geiger on the 



For convenience the tape was measured up in four parts, 

 the results of which are given separately in horizontal columns 

 I. to IV. 



For example (see column I.), out of 792 intervals of 

 1/8 minute, in which 3179 a particles were counted, the 

 number of intervals giving 3 a. particles was 152. Combining 

 the four columns, it is seen that out of 2608 intervals containing 

 10,097 particles, the number of times that 3 a particles were 

 observed was 525. The number calculated from the equation 

 was the same, viz. 525. It will be seen that, on the whole, 

 theory and experiment are in excellent accord. The difference 

 is most marked for four a particles, where the observed number 

 is nearly 5 per cent, larger than the theoretical. The number 

 of a particles counted was far too small to fix with certainty 

 the number of groups to be expected for a large value of n, 

 where the probability of the occurrence is very small. It 

 will be observed that the agreement between theory and 

 experiment is good even for 10 and 11 particles, where the 

 probability of the occurrence of the latter number in an 

 interval is less than 1 part in 600. The closeness of the 

 agreement is no doubt accidental. The relation between 

 theory and experiment is shown in fig. 1 for the results given 

 in Table I., where the o represent observed points and the 

 broken line the theoretical curve. 



Fio. 1 



2 4 6 8 10 )2 



Number or <* /articles in interval 



The results have also been analysed for 1/4 minute intervals. 

 This has been done in two ways, which give two different 

 sets of numbers. For example, let A, B, C, D, E represent 

 the number of a particles observed in successive 1/8 minute 

 intervals. One set of results, given in Table A, is obtained by 

 adding A + B, C + D, &c. ; the other set, given in Table B, 



