ON THE EARTHQUAKE AND VOLCANIC PHENOMENA OF JAPAN. 151 



assistant of the Meteorological Bureau, who has worked with me, pointing 

 out doubtful information, translating paj^ers, calculating areas, determining 

 centres, tilling in maps, and in carrying out other tedious operations for 

 the last twelve months. 



The chief reason for terminating the catalogues at the end of 1892 is 

 because the material subsequent to that date has not yet been reduced to 

 the map form, and to examine all the documents necessary to accomplish 

 tliis would have occupied at least another year ; also it may be added that 

 what has been done is in all probability sufficient to determine whether 

 work of this description is likely to lead to results of sufficient importance 

 to guarantee its continuance. 



(6) Explanation of tlie Catalogues. 



In the first catalogue the shocks are placed in chronological order from 

 1 to 8,331. When disturbances have apparently been simultaneous in 

 two distant localities, they are included under a single number. 



In the second and third columns the date and time for each disturbance 

 are given. When the latter is noted to seconds, the record refers to the 

 commencement of motion at an observatory, like that in Tokio, which is 

 provided with automatic chronogiaphs. Until the end of 1887, these 

 recoi'ds, Mhich are practically correct, refer to Tokio mean time, or 

 9 hr. 19 min. 1 sec. before Greenwich mean time. Subsequently to this date 

 the times given are those of Long. 135° E.,or nine hours before Greenwich 

 mean time. The other time records are only approximately correct, and. 

 cannot be used in any investigation relating to the velocity Avith which 

 earthquake motion is propagated. 



The fourth column gives in square ri (1 square ri=5-96 square miles) 

 the land area which was shaken. For small shocks which were only felt 

 at one or two stations the determination of this quantity has largely 

 depended upon the judgment of the observer. The figures given are those 

 obtained from the maps by means of a planimeter and entered in the 

 records of the Meteorological Department. In the second catalogue, based 

 upon a second inspection of the maps, it will be noticed that many mate- 

 rial alterations have been made in these quantities. In many instances 

 the land areas of the first catalogue are total areas, but in others they only 

 represent an insignificant portion of a disturbed tract, the centre of which 

 was beneath the bed of the ocean. The limits of the areas given are those 

 places round an origin up to which the movement was perceptible to 

 people or sufficiently strong to have been recorded by ordinai-y seismo- 

 graphs. With instruments like delicately adjusted horizontal pendulums, 

 there is no doubt that movements might have been detected far beyond these 

 arbitrary limits. For example, shock number 4,145 has assigned to it a 

 land area of 15,750 sq. ri, when we have good reasons for believing that 

 with suitable instruments it might have been noted at any point upon the 

 surface of our globe. 



The number in the fifth column approximately indicates, as shown 

 upon the key map, the epicentre of a disturbance, or a number on the 

 coast line nearest to a submarine origin. In the second catalogue, the 

 position of a submarine origin, by means of a distance in tens of miles 

 and the direction in which it is to be measui-ed from a central number, is 

 defined more closely. On the key map the numbers referring to squares, 



