io8 



NATURE 



\yune 2, 1887 



zontal motion continued during several revolutions. To 

 avoid confusion only the first of these is reproduced in 

 the figure : the motions which occurred subsequently 

 were smaller, and, as usual, the disturbance subsided 

 very gradually. The circles in which the three com- 

 ponents are recorded have been arranged so that simul- 

 taneous motions are on the same radius. Radial straight 



lines, where they are drawn, mark seconds of time. The 

 disturbance begins at a^ b, and c in Fig. r. In its early 

 portion it is marked very conspicuously by a feature 

 which has been noticed (also at the beginning) in previous 

 records — the presence of short- period oscillations super- 

 posed on larger and slower motions. These are particu- 

 larly well defined in the horizontal motion, where they 



Fig. I. 



-Earthquake recorded at the T'nivtrsity, Hongo, Tokio, Tapan, January 15, 1887, 6.52 p.m., by Prof. Sekiya. The horizontal motion is magnified 

 i"8 times ; the vertical motion is magnified 29 times ; the radial lines mark seconds of time. 



occur, during the first part of the disturbance, with a 

 period of about one-sixth of a second, or with about 

 twelve times the frequency of the principal motions. The 

 greatest amplitude of horizontal motion is found when 

 these small oscillations have nearly died out, at the 

 place marked A. By that time the vertical motion has 

 become comparatively small, A few seconds later two 



considerable vertical oscillations appear on the record ; 

 but the vertical component is, by a long way, the first to 

 vanish. In the original record the horizontal components 

 are each magnified five times, and the vertical component 

 eight times : the same ratio between horizontal and 

 vertical multiplication is of course maintained in the 

 figure given here. At three places, A, B, and C, the 



