K S. Holden — Earthquakes in California. 393 



and in the Hand Booh of the Observatory, (page 54). The 

 complete set of instruments will give for each shock the time 

 of its beginning, and that of every tremor ; the amplitude of 

 the vibration in the east and west, the north and south, the up 

 and down directions at every instant. Such a complete set of 

 instruments requires continual attention and is far too delicate 

 and troublesome in adjustment for general use. The Duplex 

 Seismometer of Professor Ewing seems, however, to be well 

 suited for general purposes. It gives with considerable accu- 

 racy, the magnitude of the earthquake force in any two 

 directions as east and west and north and south. The vertical 

 component is not registered, and the time of occurrence must 

 be taken from a watch. CojDies of this instrument can be had 

 from the California Electrical Works (35 Market street, San 

 Francisco), for $15. It therefore seems to be a suitable pattern 

 for use in California, and elsewhere, since it combines compar- 

 ative accuracy, with cheapness. A complete set of Professor 

 Ewing's instruments, is provided as I have said, at the Lick 

 Observatory. The duplex seismometers multiply four times ; 

 while the vertical component is multiplied 1 t 6 q- times, the 

 horizontal component 3-^ times in the complete instrument. 



Another complete set, exactly similar, belongs to the Univer- 

 sity of California, at Berkeley, and is installed at the Student's 

 Observatory there, under charge of Professor Soule. This 

 Observatory also has a Gray-Milne seismometer, complete. 

 Copies of the duplex seismometer are set up also at the 

 following stations : 



(1.) San Francisco, near Cliff House, residence of Hon. A. 

 Sutro. 



(2.) San Francisco, 917 Pine street, residence of Hon. J. R. 

 Jarboe. 



(3.) Chabot Observatory, Oakland, in charge of Mr. Burck- 

 h alter. 



(4.) Private Observatory of Mr. Blinn in East Oakland. 



(5.) Kono Tayee, Clear Lake, residence of Capt. R. S. Floyd. 



(6.) Observatory of University of the Pacific, San Jose, in 

 charge of Professor Higbie. 



(7.) Students' Observatory, Berkeley, in chai'ge of Professor 

 Soule. 



(8.) One will be shortly installed at Smith Creek Hotel, at the 

 foot of Mt. Hamilton. 



(9.) Office of State Weather Bureau, Cai'son, Nevada, in charge 

 of Charles Freund, Esq. 



Copies of this instrument are also in possession of Warner 

 and Swasey of Cleveland, and of Capt. C. E. Button, of the 

 U. S. Geological Survey for experiments. I believe that one 

 will be shortly mounted at the Blue Hill Observatory, near 



