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U Diversity of California Publications. 



[Geology 



be very violent in the immediate neighborhood of their origin, 

 die out at a very short distance from it. and, indeed, this is one 

 criterion actually used to determine in which class a particular 

 shock should be put. 



Researches in science are like explorations in an unknown 

 -country. The careful explorer maps his route and determines 

 carefully his position with respect to known places from which 

 he starts; he gradually maps the country he traverses, deter- 

 mining the positions of the mountain ranges, the courses of the 

 rivers and so on. He may from some vantage ground obtain a 

 glimpse of distant regions and of broad rivers, and he may make 

 a fairly good guess as to what part these rivers play in the 

 drainage of the country; but this is merely a guess, and he must 

 proceed step by step, laying down his position and the positions 

 of the topographic features in order to get a true and exact 

 knowledge of the interior, and a correct conception of the courses 

 of these rivers. So it is in science. At certain moments we form 

 conceptions of phenomena which may, or may not, be correct. 

 We must not be satisfied with this, but by patient reasoning, by 

 careful observation and, where possible, by experiments, we must 

 gradually weed out the error and prove the truth and thus 

 establish a new starting point for future advances. It is by 

 such methods and only by such methods that we can increase 

 our knowledge of earthquakes. 



Let us then examine what occurs at the time of earthquakes 

 and by a careful comparison with known physical laws, try to 

 discover the actual process of events. We cannot do better than 

 to take for our example the great California earthquake of 

 April 18, 1906, which occurred a little after five o'clock in the 

 morning, and produced such disastrous results. Great praise is 

 due to the energy of the scientific men of the Pacific Coast, who 

 promptly induced the Governor of the State of California to 

 appoint a commission to investigate the earthquake, the necessary 

 funds being supplied by the liberality of the Carnegie Institu- 

 tion of Washington. The great mass of facts collected, together 

 with a discussion of them, are contained in the report of the 

 Commission, which was published by the Carnegie Institution. 

 It is impossible and, indeed unnecessary, to repeat all these 



