Intelligence and Miscellaneous Articles. 75 



3. ' On the Distribution in Space of the Accessor}- Shocks of the 

 Great Japanese Earthquake of 1891.' By Charles Davison, Sc.D., 

 E.G.S. 



The object of the author in this paper is to consider the geo- 

 graphical distribution of the numerous shocks which preceded and 

 followed the great earthquake of 1891. A brief summary of 

 Prof. Omori's work on the distribution of the after- shocks of this 

 earthquake is given, and the difference between his method of 

 treatment and that adopted in the present paper pointed out ; the 

 author furthermore indicates possible sources of error in his maps, 

 and explains how these may be practically neglected. 



In a map of the coast within the Mino-Owari district, the 

 boundary of the area over which the principal shock was felt is 

 enclosed by a line which bifurcates towards the south. The longer 

 axis of this area coincides generally, as shown by Prof. Koto, with 

 the direction of a fault-scarp which, however, is only prolonged 

 into the south-eastern fork of the disturbed area. This the author 

 speaks of as the main fault, and he infers the evidence of a secondary 

 fault running along the southern fork. 



In discussing the preparation for the great earthquake, reasons 

 are given for believing that the distribution of earthquakes in 

 1890-91 was little, if at all, due to the marked shock of May 12th, 

 1889, but that the earthquakes of these years were preparatory to 

 the great earthquake, the consequent relief at numerous and 

 widely distributed points equalizing the effective strain along the 

 whole fault-system, and so clearing the way for one or more almost 

 instantaneous slips along its entire length. This outlining of the 

 fault-system points to the previous existence of the faults, and 

 implies that the great earthquake was due not to the rupturing of 

 the strata, but probably to the intense friction called into action by 

 the sudden displacement. 



The distribution of the after-shocks is then discussed, and it is 

 maintained that the after-shocks of the Mino-Owari earthquake for 

 the first fourteen months were subject to the following conditions : — 

 decline of frequency, decrease in the area of seismic action, and a 

 gradual but oscillating withdrawal of that action to a more or less 

 central district. 



XII. Intelligence and Miscellaneous Articles. 



ON THE ACTION OF RONTGEN BAYS ON A JET OF STEAM. 

 BY FRANZ RICHARZ. 

 T)ROF. RONTGEN has already found that air traversed by his 

 J- rays becomes an electrical conductor, and this property lasts for 

 a short time even when the Rontgen rays no longer pass. According 

 to the theory first put forward by Hr. W. Giese and Prof. Arthur 

 Schuster, electricity is conducted in gases by dissociated atoms, 

 by " ions," — a theory which has been powerfully confirmed by 

 many experiments*. Robert von Helmholtz, in a research published 

 * See Wiedemann's Annalen, vol. lii. p. 389 (1894). 



