138 F. OMORi : 



At first, waves of both kinds occurred together (superposed 

 by some traces of the proper motion of the horizontnl pendulum, 

 which, however, are easily distinguishable, on account of the 

 great length of the period of the pendulum itself). The small 

 movements,^?, q, qr, st, etc., belong to the first kind, while the 

 large displacements, a b c, c d e, etc., belong to the second kind. 

 It will easily be observed that the waves of the first kind soon 

 disappeared, leaving behind only those of the second. 



The range of motion of the principal displacements of the 

 waves of the second kind, which I assume to be horizontal 

 movements and not tiltings of the ground, (see § 26 bel()w) were 

 as follows : — 



Displacement. 

 a b 

 be 

 d e 



f9 



Again, the periods of vibration of the two Avaves, abc and 

 c d e, were respectively 5.8 and 7.9 seconds. Tf the period of the 

 motion /"^ be assumed to be 8 seconds, we find hy calculation 



maximum velocity = ö mm. per sec, 



maximum acceleration = 3.5 mm. per sec. per sec. 



These values of the maximum velocity and the maximum 

 acceleration are very low, a fact which explains why we do not 

 feel such movements. The range of motion of one of the 

 principal displacements of the first kind, s, was 2.3 mm. 



This earthquake enables us on account of its great duration 

 to calculate the average periods in several portions of its motion. 

 Beginning with a point marked B in the diagram, I find for 



