128 KEPOiiT— 1891. 



tity V^/a. In two cases where fracture may have occurred at a bad 

 joiat the quantity V^/a Avas more near to a when F=4'l lbs. 



As an illustration of the practical ajDplication of the above investiga- 

 tion, let us assume that the greatest maximum acceleration to be expected 

 is 1,000 mm. per sec. per sec, which is a quantity four times greater 

 than anything yet recorded in Tokio, and then determine the height to 

 which a brick column 2 feet square may be built above its foundations 

 and be able to withstand this motion. 



If X is the height required and iv the weight of one cubic inch of 

 l)rickwork=:'0608 lbs., then by substitution we derive from the above 

 formula 





When F=5 lbs. then .'c=6ft. Sin. 

 When F=151bs. then a^=llft. 7 in. 



A detailed account of the relationship of this formula to the formula 

 previously emjaloyed, together with a^n account of the experiments, is 

 being offered by myself and Mr. F. Omori, a graduate of the Imperial 

 University, to the Institution of Civil Engineers. 



For assistance in carrying out the experiments my thanks are due 

 to Mr. D. Larrien, who provided the truck and rails on which the 

 experiments were made ; Mr. K. Tatsuno, Professor of Architectui'e, who 

 designed and built the walls and columns ; the authorities of the Univer- 

 sity, who provided the workshop and workmen, to Mr. Y. Yaniagawa, 

 who superintended the electrical appliances ; and, finally, to my colleagues, 

 who from time to time rendered valuable assistance. 



Earthquakes in Connection with Electric and Magnetic Phenomena. 

 1. Magnetic Phenomena. 



The conclusion to be derived from the notes relating to magnetic 

 phenomena and earthquakes published in the Report for last year was 

 that, for Tokio at least, the records of the Magnetic Observatory, which 

 is continually being shaken by earthquakes, only show disturbances 

 which may be the result of mechanically-produced movements. Since 

 then I have read an account of the experiment of M. Mourreaux, chief of 

 the Magnetic Observatory of Pare Saint-Maur, near Paris. Having had 

 his instruments disturbed at the time of earthquakes, M. Mourreaux 

 suspended on the same stand as the magnetograph a copper bar having 

 the same foi-m as the magnetic one. The bifilar suspension for the copper 

 bar was made identical with that used for the magnet, and the movements 

 of each were recorded photographically. 



With three earthquakes the records for the magnet were disturbed, 

 whilst the records for the copper bar were not disturbed. This experi- 

 ment has been discussed by G. Agamemnone (' Atti dellaKeale Accademia 

 dei Lincei,' vol. vi., January 5, 1890), who points out that for various 

 reasons the period of the copper bar and the magnet must be different, 

 and, therefore, by a given movement one might be caused to move whilst 

 the other remained at rest— -a conclusion with which the present writer 

 concurs. 



Near an active volcano, where masses of magnetic matter may be 



