74 REPORTS ON THE STATE OF SCIENCE. — 1915. 



can be used in studying the residuals. Thus, in the quake of July i, 

 1914, the following residuals : 



Station. Machine. 



Graz .... W 



Zagreb. ... W 



are to be considered subject to corrections +19 s. and -j-il s. approxi- 

 mately (change sign of tabulated corrections, which apply to the C in 

 0— C). Similarly, those for Pulkovo —9 s. and —28 s. are subject to 

 corrections (A=85-2°) + 8 s. and +24 s. 



XII. Shide Bulletins. 



From Jamiary 1914 the Shide Bulletins have been arranged with 

 a view to the ultimate discussion of the best material. Earthquakes 

 not observed at many stations appear only on the ' chart ' as in the pre- 

 vious year's records ; but for the better observed earthquakes, whereas 

 for 1913 the recorded times were printed without discussion, from Janu- 

 ary 1914 they have been compared with calculated times. Epicentres 

 were at first adopted from the Pulkovo determination simply ; but as 

 it was found that these were often sensibly in error (owing partly to the 

 errors of the tables) fresh determinations of epicentre have been recently 

 made at Shide. 



The preparation of these bulletins has very considerably increased 

 the work at Shide ; but it is hoped that the extra work is profitable. 



XIII. New Method of Computation. 



Some of the labour has been abridged by the adoption of a new method 

 for calculating the distance of a station from an epicentre. If (/■, d) be 

 the longitude and latitude of a station, (L, D) those of the epicentre, 

 and if we put 



a = cos I cos d b = ain I cos d c = sin rf 



A= cos L cos D B=sin L cos D C= sin D 



then the formula used is 



2 versin A = (a_A)-+(6-B)=-|-(c-C)-. 



The quantities a, i, c are constants for the stations and have been tabu- 

 lated. A, B, C are readily formed for each epicentre. A table of squares 

 to 4 figures is amply sufficient to give the [a — A)^, &c., and a table has 

 been formed of 2 versin A which saves even the division by 2. A fuller 

 description of the process and the table for 2 versin -2^ will be found in 

 ' Mon. Not. R.A.S.,' Ixxv. p. 530. 



XIV. Standardizing a Milne-Shaw Seismograph. 



[This section is kindly contributed by the Superintendent of the 

 Meteorological Office. It was written by Mr. L. P. Richardson, of 

 Eskdalemuir, and was completed on September 3.] 



This instrument (No. 3) was set up at Eskdalemuir, in July 1915, by 

 Mr. J. J. Shaw. A description of it will be found in Section VI. of this 

 Report. 



The pivoted mirror and the link which connects it to the boom are 

 both very light, and in the first instance the instrument has been re 

 garded as a simple boom connected to a massless multiplying device. 

 The theory of such a boom is set out in most text-books on seismology. 



