MICHIGAN ACADEMY OF SCIENCE. 45 



As a modern scientific theory the earthquake centrum dates from the elab- 

 orate description by Mallet of the great Neapolitan earthquake of 1857. 

 How firmly the idea was then implanted is shown by the fact that ]\Iallet 

 made no attempt to prove the existence of a centrum, but devoted all his 

 energies to fix its location. By methods which are now known to be wholly 

 unreliable he obtained a great number of results ranging with noteworthy 

 uniformity from depths of 10,000 to 45,000 feet, and it is significant of his 

 state of mind in respect to the certainty of a centrum, that he adopted the 

 average depth for its exact position. His assumption was, in short, that 

 within this subterranean "focal cavity" gases were imprisoned and their 

 struggles to liberate themselves sent waves in all directions with equal ve- 

 locities. These waves would reach the sin-face of the earth first at a point 

 immediately above the centrum — the epicentrum — and at later instants 

 the disturbed points would be situated upon lines roughly circular in outline 

 and surrounding the epicentrum with successively larger and larger diam- 

 eters. This conception of the cause of earthquakes rendered it manifestly 

 impossible to establish relations between earthquake shocks and the geological 

 structure of the country, and thus the field of seismology came to be yielded 

 by geologists to a group of applied mathematicians now generally referred 

 to as elasticians. For nearly half a century the centrum theory has now 

 been orthodox doctrine, and an elaborate superstructure of ingenious math- 

 ematical deduction has been raised upon it as a foundation. 



The revelation that large earthf[uakes and volcanic eruptions within the 

 same province are not sympathetically related, has removed at one stroke 

 the raison d'etre of the centrum idea. It is also a significant fact that the 

 great achievements in seismology during the past twelve years have been 

 reached by studies which have largely ignored the orthodox faith of the 

 science. 



The history of science has furnished many examples of theories which 

 have contained a small element only of truth, but yet enough to suggest 

 experimentation and to widen the field of study. Such theories have evolved 

 through enlargement of the true and elimination of the false. The centrum 

 earthquake theory illustrates a false though cjuite plausible assumption, 

 the effect of which has been like a bandage l)ef()re the eyes shutting out the 

 light and involving in deep mystery even the simplest of natural phenomena. 

 It will be my endeavor in the brief time that I may claim j^our attention 

 to present earthquakes in a new light, or, in other words, as geological phe- 

 nomena to be studied in relation to the changes in the earth's surface by which 

 they are accompanied, and upon which they appear to depend. 



In order to bring before our minds the more important of earthquake 

 phenomena we may profitably consider for a few moments the great Indian 

 earthquake of 1897, which deserves to rank with the greatest in history. 

 No earthciuake has been more fully or more ably studied, and the results, well 

 illustrated, completely fill a bulky volume of the Memoirs of the Geological 

 Survey of India. Almost the total damage which resulted from this earth- 

 quake was the result of the initial shock, and all destruction occurred within 

 the first fifteen seconds of the disturbance. Before two and a half minutes 

 had elapsed all of the heavy shocks had passed, l)ut in this brief interval of 

 time an area of one and three-quarters millions of square miles had been 

 shaken, and one hundred and fifty thousand square miles had been laid in 

 ruins. 



A member of the staff of the Geological Survey of India, who was in the 

 town of Shiliong at the time of the earthquake, has stated that a rum1)ling 



