EARTHQUAKES OX THE PACIFIC C0A8T 127 



by some that the shock of Nov. 18 may have produced this shoal 

 which is not down on the charts. 

 East Oakland: Mr. Blinn's Observatory. The tirst shock was severe 

 (VI), lasting about two seconds. The time was very approxi- 

 mately 2h. 27m. 57s. (Blinn). ]\lr. Irelan gives 2h. 27m. 5Js. 

 Trees and hedges were seen to move. A few light articles were 

 overthrown, pictures were displaced, a clock was stopped (its pen- 

 dulum was in the plane N. E. 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 1 mm. in diameter. The third 

 shock was (III) at oh. 38m. 4.5s. p. m. The trace on the duplex 

 seismometer begins in an ellipse 2 mm. E. and W., 1 mm. N. and 

 S., and then there is a confused record of trembling 3 mm. N. 

 W. and S. E. by l^A mm. at right angles to this. 



1888. 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. 2914111. — 

 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 (V), time 

 3.28.8.— E. S. H. 



The duplex seismometer gives a record (magnified) beginning with 

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

 trace to the N. E. 1% 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 1 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 1 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 

 V2 of a millimeter, and their period appears to be about 14 a 

 second. 



The north and smith vibrations are well marked. From the zero 

 beat (beginning) until l^/i beats there are marked tremors. 

 From 11/4 beats to 4% beats vibrations having a double amplitude 

 of about one-half a millimeter, and a period of about '^4. to 14 

 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 com- 



