1908-7. TRANSACTIONS. 141 



panying the earthquake; only about 200 escaped. Ships were 

 thrown high and dry over Callao. 



In reading the descriptions of these old earthquakes one can- 

 not but perceive a certain mental attitude of the people towards 

 the phenomenon, and that attitude may best perhaps be ex- 

 pressed by saying with Shakespeare "Conscience does make 

 cowards of us all. " 



The San Francisco earthquake so fresh in your minds, and 

 which has been so much described and illustrated, will be dealt 

 with briefly. The great mountain masses in California running 

 parallel to the coast, and the adjoining ocean depths of the Pacific 

 are conducive, as already indicated, to earthciuakes. The break 

 would naturally occur about midway between these depths and 

 the mountains, and furthermore along the weakest line thereabouts, 

 that is, along an old geological fault, as was actually found to be 

 the case. The displacemej;it of the surface adjoined this old 

 fault or rift, which runs northwest-southeast in an almost ma- 

 thematical straight line for several hundred miles. The nearer 

 to this line, the greater was the displacement or earth movement. 

 Along the rift the greatest horizontal shifting was 16^ feet, the 

 western side moving northward, while the eastern side moved 

 southward. The maximum vertical motion was about 4 feet. 



It may be mentioned that our Ottawa Observatory seismo- 

 graph registered the arrival of the first tremor or shock seven and 

 a third minutes after its occurrence, which is equivalent to a 

 speed of transmission of 340 miles per minute. 



The disturbing force varies probably inversely as the square 

 of the distance from the rift, but as far as destruction to buildings 

 is concerned it depends very materially too on the nature of the 

 ground upon which the building stands. This was well illustrated 

 at San Francisco, where the earthquake damage was almost ex- 

 clusively confined to made or alluvial ground, that part of the 

 city that had been reclaimed from the tide fiats. This is an im- 

 portant point and one that will not be forgotten in future con- 

 struction in earthquake areas. 



The Kingston earthquake of last January, although more 

 destructive of life than the San Francisco one, yet as a world- 

 shaking phenomenon was very much smaller than the California 

 one of last April, for the minimum ampHtude or swing of the 

 recording instrument at Ottawa was nearly twenty times greater 

 for the latter than for the former. Earthquakes are generally 



