82 REPORT— 1903. 



Earthquake Frequency. — The number of earthquakes recorded wore as 



follows : — 



July to December, 1902 . Bidston, 69 Shide, 40 Edinburgh, 37 Kew, 30 



During the year 1903 . „ 134 „ 78 „ 70 „ 64 



During 11 months in 1901 . „ _94 „ 90 „ 85 „ 63 



Total for two years 228 1G8 loo 127 



Each of the earthquakes considered was recorded at more than one 

 station, and therefore it is exti-emely unlikely that artificially produced 

 disturbances have been included in the computations. 



Earthquake Duration. — Between July and December there were ten 

 earthquakes, each of which was recorded at all four stations. The total 

 number of minutes which the instruments were caused to move by these 

 disturbances were : — Edinburgh, 691 ; Kew, 610 ; Shide, 606 ; and 

 Bidston, 545. 



Amplitudes — The sum of the maximum amplitudes in millimetres for 

 ten earthquakes was as follows : — Shide, 19-4 ; Kew, 14-1 ; Edinburgh, 

 12-0 ; Bidston, 9-0. 



These quantities regarded as angular displacements may be respectively 

 read as 9"-7, 7"'2, 6"-5, and 4"-5. Add to these the corresponding 

 quantities for earthquakes recorded between January and June, then the 

 totals for the year 1902 are : Edinburgh, 21"-5 ; Shide, 2r'-l ; Kew, 20"-9 ; 

 and Bidston, 13" -2. 



If in making these comparisons the large earthquakes are omitted, 

 then the amplitudes of motion as recorded at different stations are 

 practically identical. 



Commencements. — Out of thirteen records (June to December 1902) 

 at Bidston the commencements have been the earliest — or not more than 

 two minutes later than those recorded at other stations — nine times, at 

 Shide seven times, at Edinburgh six times, and at Kew three times. 



Conclusion. — For the present, at least, the conclusions arrived at are 

 as follows : — • 



1. Bidston records the greater number of earthquakes and obtains 

 earlier commencements for the preliminary tremors more frequently than 

 at other stations. 



The durations and amplitudes recorded at Bidston are less than at 

 other stations. 



2. Kew records the least number of disturbances, and commencements 

 are frequently late. Durations and amplitudes are similar to those 

 obtaining at Shide. 



3. At Edinburgh and Shide, frequency, time of commencement, and 

 amplitude are similar, but at the former station the duration is greater 

 than at the latter. 



VI. Earthquake Commenceineitts as recorded at Strasshurg and 



in Britain. 



The records referred to in the' following note are those obtained in 

 1902 from the Rebeur-Ehlert pendulums at Strassburg or Hamburgh 

 and the Milne pendulums installed at Kew, Shide, Bidston, and Edin- 

 burgh. The multiplication of the Strassburg apparatus is about eight 



' See B.A. Report, 1898, p. 268. 



