HoGBEN. — The Wanganui Earthquake. 589 



and B, even if the times are those of the maxima farthest 

 apart in time, unless we assume a much greater duration of 

 the earthquake than the recorded facts allow us to assume, or 

 unless we suppose the possibility of errors of observation in 

 no way warranted by the character of the returns, which bear 

 internal marks of accuracy, and show in each class a remark- 

 able agreement, Gisborne and Greymouth being the only 

 places where the error amounts to half a minute (and these 

 were not used in the calculation). If the velocities are dif- 

 ferent the times cannot well be times relating to different 

 maxima of the same series of waves, for the velocity of pro- 

 pagation of the waves of any series will be constant at the 

 origin.^' The position of S is not affected by the question just 

 discussed. 



The velocity — eighty-five miles per minute, or, say, 7,500 ft. 

 per second (for the A places) — is the highest yet found for 

 any New Zealand earthquake, the velocity in the Nelson, 

 1893 — about fifty miles per minute, or 4,400 ft. per second — 

 being the only one at all near it. 



The maximum intensity measured by the acceleration of 

 the earth particle at the surface at Wanganui was about 

 800 mm. to 900 mm. per second^ say, one-twelfth of that 

 due to gravity — according to Holden's mechanical equivalents 

 of the Eossi-Forel scale.! 



The amplitude or the period we have no means of mea- 

 suring, and consequently cannot find the wave-length. 



I have drawn the probable isoseismal for the intensity vi. 

 on the Eossi-Forel scale, and partly those for vii. and viii. 



On the map I have marked the positions of the epicentra 

 of all the earthquakes of this district for which the data were 

 full and accurate enough for mathematical purposes. They 

 are as follows (approximately) : — ■ 



F. Feb. 20, 1890 ... Trans. A. A. A. S., 1891, "New 



Zealand Earthquakes." 



K.Dec. 4,1891... Trans. N.Z. Inst., xxv., p. 362. 



A. July 5, 1891 ... Trans. N.Z. Inst., xxiv., p. 



577. 



P. Aug. 20, 1891 ... 



Q. May 18, 1893 ... 

 E. or S. Dec. 8, 1897 ... J- Now first published. 



T. May 16, 1898 ... 



V. July 8, 1898 ... J 



A large number of other shocks agree generally, as far as 



* Ibbetson, " Elasticity Arts," 268 and 276. 



t Holden, American Journal of Science, June, 1888 ; Hogben, 

 " Earthquake Intensity in Australasia" [Trans. A.A.A.S., 1893). 



