440 ANNUAL KEPORT SMITHSONIAN INSTITUTION, 1908. 



steel. We had no ground for assuming that it was not absohitely 

 rigid. The pole oscillations, on the other hand, demonstrate that the 

 earth is not absolutely, but only relatively, rigid, and they indicate 

 the degree of rigidity. 



Far greater yet is the degree of precision which our conclusions 

 many attain along another line of research, to wit, that of earth- 

 quakes. 



The awful phenomena of earthquakes, in which the firmest thing 

 we know — the ground on which we walk — begins to shake, and in 

 which often in a few moments all human work is reduced to ruins 

 and thousands of human lives destroyed, have always powerfully at- 

 tracted the attention of men. Fervid fancy was tireless in picturing 

 ever new horrors. It was supposed that the tremors were due to the 

 movements of fabulous monsters, or to the malign fury of demons, 

 or to the anger of the deity. With the increase of civilization, natural 

 science began to occupy itself with the phenomena of earthquakes. 

 At the present day civilized nations have united in common syste- 

 matic work. The Gottingen Geophysical Institute on the Hainberg 

 represents one of the German seismologic stations. For some jears 

 the Gottingen Scientific Society has maintained a station for geo- 

 physical obs3rvations in the tropical belt of the Pacific, at Apia, on 

 German Samoa, and one of its adjuncts is a seismologic station. 



At first the observation of earthquakes was naturally confined to 

 the direct investigation of the traces left by them. Soon, however, 

 special instruments were employed in order to gain a more accurate 

 idea of the nature and magnitude of the earthquake movements. As 

 these instruments were improved, the scope within which tremors 

 could be observed at a distance from their focus grew wider. Finally 

 it appeared that instruments of sufficient delicacy are able to record 

 the tremors produced by every large earthquake originating anywhere 

 on the globe. Since that time — from about 1890 onward — earthquake 

 investigation gained a mightj^ impulse; for the observer was hence- 

 forward no longer confined to local investigations, but enabled to 

 trace the earthquake processes of the whole earth from any station, no 

 matter where situated. 



Science asks. What is the significance of earthquakes in the history 

 of the development of the earth? ^^liat is the nature of the shocks 

 that are propagated to a distance? What paths do they follow? 

 What do they tell us regarding the condition of the globe ? Anxious 

 humanity will also demand an answer to the further question. How 

 can we know what localities are endangered, what antecedent symp- 

 toms may be used as warnings, and what sort of structures must be 

 erected in order to afford protection? 



You see the tasks are numerous and involve profound interests of 

 science and of human life. Thus we can understand the extraordinary 



