E. S. Holden— Earthquakes in California. 401 



supposed by some that the shock of Nov. 18 may have pro- 

 duced this shoal which is not down on the charts. 



East Oakland : Mr. Blinn's Observatory. The first shock 

 was severe (VI) lasting about two seconds. The time was very 

 approximately 2h. 27m. 57s. (Blinn). Mr. Irelan gives 2h. 

 27m. 54s. Trees and hedges were seen to move. A few light 

 articles were overthrown, pictures were displaced, a clock was 

 stopped, (its pendulum was in the plane ISLE, and S.W.) ; 5 

 chimneys were thrown down on 23d avenue ; a noise was heard 

 after the first shock. The second shock was (II) at 3:48 P. M. 

 The duplex seismometer trace is a loop about l mm in diametor. 

 The third shock was (III) at 5h. 38m. 45s. P. M. The trace on 

 the duplex seismometer begins in an ellipse 2 mm E. and W., 

 1™ 1ST. and S., and then there is a confused record of tremb- 

 ling 3™™ KW. and S.E. by li mm at right angles to this. 



December 11, 3:29 p. m. — Lick Observatory : the shock was 

 sudden and (IV) in intensity. Time by watch 3h. 28m. 59s. ; 

 by earthquake clock 3h. 29^m. — J. E. K. A humming noise 

 was heard after the shocks. There were two such at an 

 interval of 2 sec. The time of the last was 3h. 28m. 58s. plus 

 or minus 3 sec— E. E. B. Intensity (Y), time 3:28.8.— E. S. H. 



The duplex seismometer gives a record (magnified) begin- 

 ning with a sharp straight trace to the N.~W. 3 mm long, then a 

 straight trace to the N.E. lf mm long, then a straight trace to 

 the N\W. nearly 2 mm long, and at the end of this the pen 

 has recorded a confused tremor in a space about l mm square. 

 The record of the Ewing seismograph is as follows : (The 

 adjustment of the marking pen for seconds has been changed 

 so that there are 95 beats of the pen to 1 min. of time.) 



There are very slight vertical tremors for the first three 

 beats ; they then vanish completely. Their period is from -§- 

 to -|- of a second of time ; their double amplitude is not above 

 ^■of a millimeter. 



The east and west vibrations last only for two beats though 

 the faintest perceptible tremor lasts until the twentieth beat 

 after the beginning. Their greatest double amplitude is not 

 above \ a millimeter, and their period appears to be about \ a 

 second. 



The north and south vibrations are well marked. From the 

 zero beat (beginning) until \\ beats there are marked tremors. 

 From \\ beats to 4f beats vibrations having a double amplitude 

 of about one half a millimeter, and a period of about -§- to \ of 

 a second time. At the end of the 6th beat the marked tremors 

 cease and a very faint tremor continues to the end of the 20th 

 beat, and possibly to the end of the 33d beat. As a basis of 

 computation we may assume from the record of the north and 

 south component : 



