Hogben. — On the Earthquake of 4th December, 1801. 365 



x), 



y). 



u), 

 w), 



279,268*+ 93,020?/+ 10,8777* -3,575w= 19,801,880 



93,020*+ 121,252// + 6,379?*— 2,119w = 7,979,392 



10,877*+ 6,379/y+ 636?*- 197?*; = 785,488 



3,675*+ 2,119//+ 197?*- 63z*> = 268,101 



Hence * = 74-46 miles, y = 24-55 miles. K (see PL XL VI.) is 

 the epicentrum thus found. It is 56£ miles from Wellington, 

 59 miles from Wanganui. The equations do not give the ab- 

 solute velocity (?* is negative), or the depth of the centrum. 

 By a method of trial we find the former to be about 7 - 7 miles 

 per minute, and the latter probably a httle less than 10 miles. 

 K is 3 miles north-east of E'. 



The absolute velocity, with the same depth of origin, but 

 with the epicentrum E', would be 8-4 miles per minute. These 

 are both very slow, especially considering the marked (though 

 not severe) character of the shock. The following table shows 

 how these two solutions agree with the best of the recorded 

 times : — 



Time at Origin K. Time at Origin E'. 



(Mean absolute velocity, (Mean absolute velocity, 

 7 - 7 miles i>er minute. 84 miles per minute. 

 Depth, 10 miles.) Depth, 10 miles.) 



gives 4h. 32 - 8min. and 4h. 33'2min. 



Place. 



Otaki 

 Picton 

 Havelock 

 Foxton 

 Wanganui 

 (Blenheim 

 Feilding 

 Opunake 

 (Wellington 

 (Masterton 



Mean* 



4h. 32-9min. 

 4h. 32-2min. 

 4h. 32-9min. 

 4h. 32-7min. 

 4h. 31'4min. 

 4h. 32-7min. 

 4h. 32-7min. 

 4h. 32-6min. 

 4h. 32-4min. 



4h. 32-7min. 



4h. 33-8min. 

 4h. 33-lmin. 

 4h. 33-2min. 

 4h. 33-lmin. 

 4h. 32-5min.) 

 4h. 33-lmin. 

 4h. 33-4min. 

 4h. 33-3min.) 

 4h. 33-lmin.) 



4h. 33-2min. 



The time at the origin should be the same from whatever 

 place we reckon back ; the close agreement, however, is worthy 

 of note. 



Intensity : Method of Isoseismals. — The intensity on the 

 Eossi-Forel scale is indicated by Eoman numbers in the last 

 column. If we trace the isoseismal corresponding to intensity 

 iv., and smooth it out into an ellipse, we shall obtain for the 

 focus of the latter one of the points I, S, S', S", according to 

 the prominence given to the estimate of the intensity at 

 different places. S r and S" are too far to the east, for Foxton 

 and Otaki must be both on or nearly on the isoseismal VIE, 

 an ellipse with the same origin as focus. None of the points 

 S, S', S" agree with the times. The focus I may be said to 

 confirm in a general way the position already found for the 



origin. 



* Excluding Blenheim, Wellington, Masterton. 





