ON SEISMOLOGICAL INVESTIGATIONS. 41 



The last instrument constructed is in charge of Mr. L. Bernacchi, of 

 the ss. ' Discovery.' If possible it is to be used in the Antarctic Regions. 

 Continuous records have been received from stations marked with an 

 asterisk, whilst Mexico, New Zealand, Trinidad, Philadelphia, and Balti- 

 more have sent occasional records. 



The last registers issued by the British Association Committee are 

 Circulars Nos. 2 and 3. These refer to Shide, Kew, Toronto, Victoria, B.C., 

 San Fernando, Cairo, Cape Town, Mauritius, Calcutta, Bombay, Kodai- 

 kanal, Batavia, and Cordova. These are complete up to the end of 

 December 1900, excepting for Cordova (Circular No. 2), the entries for 

 which end on June 21, 1900. 



The instruments now in use at the Shide station are : — 



1. A photographic recording horizontal pendulum oriented North and 

 South, This is the type of instrument similar to those at other stations. 



2. A pair of pendulums similar to the above oriented North-South 

 and East- West. This instrument was kindly presented to your Secretary 

 by Mr. A. F. Yarrow. 



3. A pair of horizontal pendulums writing On smoked paper. These 

 have arms 14 inches in length, and each carries a 10 lb. weight. 



4. A pair of horizontal pendulums also writing on smoked paper 

 The arms are 9 feet in length, and each weighs about 100 lb. This and 

 instrument No. 3 give open diagrams. 



5. A simple spiral spring seismograph for vertical motion. Record 

 photographic. 



6. A large balance arranged to show tilting. 



Analyses of Records for 1900. 



An analysis of the earthquakes recorded during the year 1900, similar 

 in character to that given in the Fifth Report issued by your Committee 

 for the records of the previous year, is in progress. Its length precludes 

 it from appearing in these reports. 



On the Approximate Frequency of EarthquaUes at different Stations. 



In the following table the large numerals to the right of or beneath 

 the name of a given station indicate the actual number of disturbances 

 recorded at that station during given intervals of time. For all stations, 

 excepting three, these intervals are the years 1899 and 1900. The three 

 exceptions are Cairo, for which the interval is the year 1900 ; Calcutta, 

 from July to December 1900 ; and Cordova, from January to June 1900. 

 Inasmuch as at all stations, for a variety of reasons, there have been 

 interruptions in the continuity of observations, these time intervals must 

 only be regarded as approximations. As it is difficult in the case of 

 certain minute disturbances to determine whether these have a seismic 

 origin or are due to some other cause, the large numerals are only approxi- 

 mations. 



The small numerals to the right or left of a large numeral give 

 the percentage of the earthquakes recorded at the station to which it refers, 

 which are common to the registers of the other stations. For example, out 

 of 210 records at Shide, 58 per cent, of them were also noted at Kew, and 



