310 C. JDavkon — British Earthquakes of 1889. 



places in the line of direction of the fault, and shortest at that 

 place situated so that a line joining it to the centre of the seismic 

 focus is perpendicular to the fault-plane. On the other hand, the 

 apparent duration depends on the distance of the place of obser- 

 vation from the focus, and, what is far more important, it depends 

 on the power of the observer to detect the faint initial and final 

 tremors. On this account, chiefly, I think it is not possible to 

 discover any certain law in the distribution of places according to 

 the duration of the shock felt there. In this respect, more may 

 be learnt from the duration of the sounds. 



The following are the recorded durations of the shock : — 



About 15 seconds. Farnworth. 



6 ,, Blackburn, Bolton. 



Crosby, Heaton Chapel, Mailing. 

 Chorley. 

 Prestwich, 



Bacup, Cheetham Hill, Crumpsall, Darwen, Meltham, 

 Preston, Waterhead, Whalley. 

 ,, 1 „ Leftwich, Oldham, Tyldesley. 



Intensity. — In the following lists are given the names of the places 

 where it was possible to determine the intensity according to the 

 Itossi-Forel scale. 



VI. Bolton, Eamsbottom, Tottington. 



V. or YI. Bury, Chesham, Farnworth. 



V. Besses, Blackburn, Chorley, Darwen, Golborne, Heywood, 

 Horwich, Hulton Park, Ince, Eochdale, Turton, Whitefield, Wigan. 



IV. or V. Blackley, Castleton, Cheetham Hill, Crumpsall, Har- 

 purhey, Littleborougla, Middleton, Prestwich. 



IV. Accrington, Altrincham, Bolton-by-Bowland, Bowdon, Breight- 

 met, Cheetham, Eccles, Facit, Heaton Park, Lees, Leigh, Leyland, 

 Little Hulton, Manchester, Milnrow, Newhey, Northwich, Whit- 

 worth, Withington. 



III. or IV. Crosby, Melling, Preston, Whalley. 



III. Meltham, Stockport, Wardleworth. 



The observations are not sufficiently numerous to enable the 

 isoseismal of intensity VI. to be drawn. All the places where the 

 intensity was V. lie, however, within a well-defined curve which is 

 shown upon the map. This curve is approximately circular. Its 

 dimensions are 22 miles from north to south, and 23 miles from east 

 to west. It includes an area of about 396 square miles. Its centre 

 is half a mile west of the village of Bradshaw and two miles N.N.E. 

 of Bolton. 



It will be noticed that, at several places within this curve, the 

 intensity is given as only IV. This may be due to one of two 

 causes. (1) The intensity may really have been more than IV., 

 but the rattling of windows, etc., may have been recorded as the 

 most noticeable effect of the shock; or (2) the intensity may have 

 been different at two neighbouring places within this isoseismal, 

 this being only what we should be led to infer from Prof. Milne's 

 seismic survey of Tokio. 



Outside this isoseismal, the places where the intensity is known, 

 though numerous, are scattered over a much greater area, and it is 



