212 REPORT — 1882. 



always constant. Sometimes the needle remained permanently deflected, 

 and at otlier times it gradually fell back towards zero. 



These currents I regard as being due to a mechanical disturbance of 

 one of the earth bar.s, causing a difference of contact with the soil ; and, 

 in consequence of this, an alteration iu the moisture, oxidation surface, 

 &c., at one end of the circuit, thus giving rise to a difference of potential 

 relatively to the other end of the circuit. 



No doubt actual earthquakes act upon the earth plates of telegraphic 

 lines in a similar manner, but the currents which are in this way pro- 

 duced at the time of an earthquake are due to different causes than those 

 which appear sometimes to have preceded earthquakes by considerable 

 intervals of time. 



In the experiment upon artificial earthquakes ray thanks are especially 

 due to Mr. T. Fujioka and Mr. M. Kuwabara, of the Imperial College of 

 Engineering, and not least of all to Mr. John Reid, agent of Nobel and 

 Co., and to Mr. Denys Larrieu, who not only furnished me -with dyna- 

 mite, but on several occasions also gave me their personal assistance. 



The great difficulties which had to be overcome in making these 

 experiments, as, for instance, obtaining dynamite from the Government 

 stores, its transportation, its storage, the difficulties in obtaining a piece 

 of ground on which to experiment, manufacturing the necessary instru- 

 ments, obtaining telegraphic wire and firing apparatus, the making of 

 electric fuses, the anxiety lest accidents should occur, the training of a 

 body of assistants, the putting in of bore-holes, the almost unexceptionally 

 bad weather which had to be encountex'ed on days for which permission 

 had been obtained, &c., have already been referred to in a letter to this 

 Association. 



For the use of the ground where the experiments were performed and 

 for the loan of numerous tents for the places where the instruments were 

 established, and for a body of attentive servants, my thanks are due to His 

 Excellency General Yamada, Minister of the Interior, and to Mr. Arai 

 Ikunosuke, Director of the Meteorological Department. For the loan of 

 telegraph wire, firing apparatus, and other instruments I tender my 

 thanks to the directors and officers of the Department of Public Works, 

 especially the Department of Imperial Telegraphs, the ^aval and War 

 Departments, and the Imperial College of Bngineei-ing. 



Although several good diagrams of actual earthquake motion were 

 obtained, in consequence of my instruments being continually removed 

 for the purpose of making experiments on artificial disturbances, each set 

 of which took several weeks' prepax'ation, many earthquakes were passed 

 by unrecorded. Had the instruments, however, been continually in their 

 places, the records would not have been so numerous as in previous years, 

 the last season being comparatively a poor one — there only being between 

 May 1881 and May 1882 fifty-seven shocks, as compared with eighty 

 which were felt during the corresponding period of the previous year. 



The greatest activity was in February and March. 



Although earthquake disturbances were comparatively few in the 

 Tokio area, the records obtained by the help of post-cards from the 

 districts north of Tokio show that during certain months there was in 

 North Japan an activity greater than was anticipated. In fact, judging 

 from the records which were obtained although the season was a poor 

 one, it was calculated that, taking Japan as a whole, there were every 

 year, on the average, two or three shocks per day, a number as great 

 as that which is usually assigned for the whole world. 



