ON SEISMOLOGICAL INVESTIGATION. 

 Table X. Origins rvliich are extremely doiibtful — continued. 



87 



The origins indicated in the last table are for the most part conjectural. 

 In those instances where a disturbance has only been recorded at Shide 

 and Kew, and we are without evidence showing that the seismograms 

 refer to earthquakes observed in Great Britain and Europe, it seems pro- 

 bable that they represent adjustments in the strata on the eastern side 

 of the North Atlantic. Time entries for these stations, a few minutes 

 later than the corresponding entry for Toronto, suggest that we are 

 here dealing with a disturbance originating on the western side of the 

 same ocean. 



Origins indicated by terms like Indian Ocean and Pacific Ocean only 

 show how little information can be derived from certain seismograms. 



Here and there a few impossible entries are recorded. For example, 

 the greatest interval of time which could elapse between the arrival of an 

 earthquake in Mauritius and Bombay or Madras is thirty minutes, yet 

 for earthquake 326 it will be observed that the entries for the latter places 

 are respectively forty-one and forty-five minutes. To correct such entries 

 it is necessary to compare together the original seismograms, which has 

 not been always possible. 



15. Illustrations of Seismograms. 



The following illustrations of seismograms are only to be regarded as 

 sketches of the original photograms. The accuracy of any given reproduc- 

 tion has been largely dependent upon the clearness of the figure from 

 which it was copied. They show the range of motion and the principal 

 characteristics of wave-groups, but they do not show details like small 

 serrations so clearly exhibited in many of the original records from which 

 they have been reproduced. The numbers correspond with the numbers 

 given for particular earthquakes in the preceding text and those in the 

 Shide records contained in the first circular of earthquake registers issued 

 by the Seismological Investigation Committee. The arrow with its time- 

 mark gives the time for a particular phase of movement, which is usually 

 that of the commencement. The number following the letter S gives the 

 time-scale in millimetres per hour. Thus S=60 means that 60 milli- 

 metres equal one hour. 



