55 



:\I A(tNETI( ' KXI'EIUMENTS. 



Tlic'R' is no magiiL-lir iiiipanitiis at piTsriit in tlio ri|ui[iiiR'iit nf tiiu (jbserva- 

 lory, nor does tliu jiliysi'al laboratory of tli- uniwrsity i)L)s^es3 any of siitKcicnt 

 ilulicacy for inakiiij:; accurate magnetic measnrcineiits. During June and July 

 1S80, Mr. Fujisawa. a special student in physics in the University, made a series 

 of observations with tlu' aid nt' such ajiplianccs as cnuld be nbtained, for the 

 purpose of det<irn)ining the liorizontul comi)onent of niagnetisni at Tokio, with 

 a view to making a com|iarison between the result and a similar series upon the 

 sunnnit i)f Fujinoyama. Although ]iretending to no great degree of accuracy the 

 results are, ])erliaps, of sufficient interest tu justit'y their ]iidilication in this 

 report. From a rejiort furnished bv I^Ir. Fujisawa the following brief account 

 of the experiments is tidjen. 



Two magnets were used in the determination. The fust ( A I was 12 cm. 

 in length, rectangular in section an<l wei^hi-tl (;s.,S3 grannnes. The secoi; 1 (I'li 

 was 1(J em. in length, rectangidar in section and weighed 57. .OS grammes. In 

 tlio determination of the horizontal component of magnetism at Tokio the 

 ordinary method was piusue<l, the operations consisting in determining the period 

 (d' vibration and tin- ih-tleetion fmni the magnetic meridian of another magni't 

 jilaced at a measured distance. The time of a single viliration was determined 

 by making a Chronographie record (d' tlie transits of a point u|i')n the end of 

 tho magnet across the vertical wiies of a telescopj placed at a distance of about 

 5 metres from the magnet. In tliis way the period of vibration of the magnet 

 could \ni obt<iined to a <lcgree of accuracy considerably exceeding tlivt attainable 

 in the other factors of the determination. The moment of inertia of the mag- 

 net was determined from its ligure, its synnnody being such as to render that 

 method sufliciently accurate. In the iletermination of the horizontal component 

 magnet (Al w;vs used ; no deflection measureme'ids were made with thi' other 



The following is one series of the results of observations lor the iiriiod of 

 this magnet; the time t}irough<put is in sidereal seconds .-uid the location for this 

 «fries was in tin- physical laboratory of the (Iniversity at Tokio. 



Jidv 1 



Time of vibration 

 10.0202 



io.C2(;o 



1O.C202 

 10.620G 

 10.0200 

 Mean 10.0227' 



Tliesf, with other results, were combined willi tin; residts of deflection ob.serva- 

 tioti«, the latter, owing to the ini|M'rfe(t nature of the apparatus, bi'ing more 

 irregular. 'I'lie mean of flve complele deli-rnduations gave for the horizontal 

 component ; 



