EARTHQUAKES ON THE PACIFIC COAST 45 



1906. January 14; Mouo Ranch. 



1906. January 16; San Francisco; 10:33 a. m. and 2 p. m. Feeble shock.— 

 A. G. McAdie. 



1906. January 17; Lick Observatory; 12:46:56 a. ni. Two light shocks, 

 ;)l)out 1 second apart. No instrumental record. 



1906. January 25; Phoenix, Arizona; 1:40 p. ni. Marked tremors and rock- 

 ing motion; north to south. This same shock, but more violent, 

 felt at Flagstaff, Ariz. — L. X. J., Weather Bureau. 



1906. January 31; Mills College. 



San Francisco; 10:.58 p. m. — A. G. McAdie. 



1906. February 26; Lick Observatory; 5:24:40 a. m. Two light shocks, 

 about a second apart. Duplex gave slight displacement to the 

 west. 



1906. March 3; Calexico, Canipo. Cuyamaca, El Cajon, Riverside, Point 

 Loma. 



San Diego; 12:24:50 p. m. Force II; direction southwest to north- 

 east. — F. A. Carpenter. 



1906. March 4; Calexico, Cuyamaca. 



1906. March 5; San Francisco; 9:30 p. m. — A. G. McAdie. 



1906. March 19; Xapa. 



1906. March 20; Cuyamaca. 



1906. April 11; Xiles; 12:54 a. m. — Wm. Barry. 



1906. April 18; San Francisco. 



The Sax Franxisco EARTiHiiAKK- 



By Prof. A. Ci. McAdie, U. ^. Weather Bureau. 



The morning of Wednesday, April 18, was clear and pleasant over 

 the greater portion of the Pacific coast. An area of high pressure 

 was moving steadily and somewhat slowly eastward over Idaho. 

 The weather map gives the conditions existing a few minutes 

 previous to the great earthquake, and it may be noted that the 

 pressure distribution is of a type which has been found to pre- 

 vail when certain earthquakes occur in California. A study of 

 the relation of atmospheric pressure and earth movement had been 

 under wav in the office of the Weather Bureau at San Francisco 

 for some "years, and while no very definite conclusions had been 

 arrived at, it was plain that the greater number of earthquakes 



