392 



NATURAL SCIENCE. 



June, 



regarded as complete, and Mr. Omori has subjected them to a careful 

 analysis, of which the principal results are summarised in this paper. 



One of the most interesting sections in Mr. Omori's memoir is 

 that on the periodicity of the fluctuations in the number of after- 

 shocks, but as this does not seem to have any necessary connexion 

 with the present subject, I have, in order to save room, omitted all 

 reference to it here. 



As the results, to a certain extent, are the same in each case, it 

 will be sufficient to describe a single earthquake in some detail, with 

 a brief reference to the others. That on which our knowledge is 

 most complete is the Mino-Owan earthquake, generally known in this 

 country as the great Japanese earthquake of 1891. 



Fig. 1. Area affected by the Earthquake of i I 

 This figure is reduced from a map appended by Mr. Omori to his paper on the 

 isoseismal lines of the great Mino-Owari earthquake of 1891. I regret that I am 

 unable to give the proper reference. But the omission is probably of little moment, 

 for the paper is written entirely in Japanese. 



The Mino-Owari Earthquake of 1891. — This great earthquake, one 

 of the most disastrous within historic times, occurred on October 28, 

 at 6.37 a.m. (mean time of 135 degrees E.). The area disturbed by it, 

 including both land and sea, was not less than 320,000 square miles. 

 Its boundary and the principal isoseismal lines 2 are shown in 

 Fig. 1. In the region enclosed by the first isoseismal, the destruction 

 of buildings was nearly complete ; in the area of the second isoseismal, 



2 " Isoseismal lines " are lines of equal intensity of the earthquake force. 



