618 BELL SYSTEM TECHNICAL JOURNAL 



and turned in to the office on each day except Sundays and holidays 

 was recorded and tabulated for the period from November 1, 1923 

 to September 30, 1925, inclusive, excluding June, July, and August 

 of each year, when there might be considerable variations in the popu- 

 lation of the building. Distribution (b4) shows the result of a count 

 of the number of times that the number 12 appeared as the last two 

 digits of a ten-place logarithm in a sample consisting of a column of 

 100 logarithms in Duffield's table,'^ and (b5) shows the number of 

 fires per day in New York City in 1924, as reported daily in The New 

 York Times, the figures for July 4 and for Election Day being discarded 

 for obvious reasons. The last four examples in this group were 

 taken from telephone company records of local service observations. 

 A sample consisted of the calls observed at one central office in one 

 month, and the series of samples used was selected from a complete 

 record for all the central offices in a large city by the requirement 

 that the number of calls per sample be not less than 450 nor more than 

 550. Distribution (b6) was obtained for the number of incorrect 

 reports, (b7) for the number of cutoffs, (b8) for the number of double 

 connections, and (b9) for the number of calls for the wrong number. 



Group three is headed by Bortkewitsch's classical example of the 

 Poisson exponential.^^ He found from the records of the Prussian 

 army the number of men killed by the kick of a horse in each of 14 

 corps in each of 20 successive years, and, after discarding the records 

 for 4 corps which were considerably larger than the others, treated 

 the rest as one series of samples. This is distribution (cl). Series 

 (c2) is similar to (b4), except that the samples of 100 two-place num- 

 bers were obtained from several different sources, logarithmic tables, 

 trigonometric tables, and numbers listed in a telephone directory. 

 Examples (c3), (c4), (c5), and (c6) show the variation in the number 

 of telephone messages recorded per five-minute interval for certain 

 groups of coin-box telephones in a large transportation terminal. 

 The number of calls registered for each of 23 such telephones in each 

 of about 20 five-minute intervals between noon and 2 p.m. was 

 recorded on each of seven days (no Saturdays or Sundays included) 

 but as the telephones are arranged in groups the distribution of the 

 number of calls per interval was calculated for each group rather 

 than for the individual telephones. These shown here are for a 

 group of two telephones (c3), a group of four (c4), another group 

 of two (c5), and a group of six (c6). The next four examples are 



18 "Logarithms, Their Nature, Computation, and Uses," by W. W. Duffield, 

 Washington, 1897. 



18 Bortkewitsch, op. cit. 



