MATHEMATICAL TABLES 269 



from this the after-shocks appeared to be independent. Search was made 

 for periodicities of the solar and lunar days and half-days, a fortnight and a 

 month, and for any evidence that returning waves tend to stimulate a new 

 shock, but no such evidence was found in any case. It appears that, except 

 within an interval very close to the main shock, after-shocks may be con- 

 sidered as related to the main shock and nothing else. 



It appears, however, that if data used in testing suggested periodicities 

 include after-shocks, the random amplitudes found would be greatly 

 increased by the dependence of the after-shocks on the main shocks of their 

 series. This makes the events occur in batches, and the usual tests for the 

 significance of an amplitude found by Fourier analysis fail. No alleged 

 periodicity can be trusted if it is based on data that include different series 

 of after-shocks. 



An analysis of deep focus earthquakes is in progress, in the hope of ob- 

 taining a test of the 20° discontinuity and improvements in the estimated 

 thicknesses of the upper layers and in the times of S at short distances. It 

 has been found that the times of P, adapted to a discontinuity and to a 

 continuous time curve that would be consistent with the data of normal 

 earthquakes, would differ by a maximum of about i-6 sec. in deep ones. 

 This is perhaps just within the range of observability if relevant data can be 

 found. 



Reappointment of the Committee. 



The Committee asks for reappointment and for the renewal of the grant 

 of £100 from the Caird Fund. 



MATHEMATICAL TABLES. 



Report of Committee on Calculation of Mathematical Tables (Prof. E. H. 

 Neville, Chairman ; Dr. A. J. Thompson, Vice-Chairman ; Dr. J. 

 WiSHART, Secretary ; Dr. W. G. Bickley, Prof. R. A. Fisher, 

 F.R.S., Dr. J. Henderson, Dr. E. L. Ince, Dr. J. O. Irwin, Dr. 

 J. C. P. Miller, Mr. Frank Robbins, Mr. D. H. Sadler, Mr. W. L. 

 Stevens and Dr. J. F. Tocher). 



General activity. — Eight meetings of the Committee have been held, in 

 London. 



The grant of £200 has been expended as follows : 



Wages and insurance for computer for forty-seven weeks 

 Calculations for Bessel functions of order greater than one 

 Calculations for Airy Integral, etc. .... 

 Secretarial and miscellaneous expenses 



Personnel. — The Committee has been particularly unfortunate this year 

 in losing by death two of its oldest members. Dr. J. R. Airey, who died on 

 16 September, 1937, joined the Committee in 1907, and remained associated 

 with it until his death. During this period he was indefatigable as a com- 

 puter, and was responsible for the production, single-handed, of a vast 

 amount of tabulating work. He was Secretary from 1920 to 1929, and 

 served as the clearing-house for tabulation work for the British Association 

 until the time when regular meetings in London became the recognised 



