MAGNETIC SURVEY OF JAPAN. 165 



him, he represents the magnetic north as being- identical with the 

 true geographical north. Dr. Naumann, in a paper on secuhu* 

 changes of" magnetic dechnation published in the Transactions of the 

 Seismological Society of Japan (\ ol V, 1883), has given an interest- 

 ing discussion of some of Inö's bearings, which seem to diiter from 

 the true bearings by amounts that can be explained only on the 

 supposition of considerable local magnetic deviations. That the 

 average value of the Declination over Japan in Inö's days was zero 

 is no doubt true ; but, by assuming his magnet to point always true 

 north and south, Inö appears to have fallen into appreciable error 

 in laying down the positions of certain of the mountains in north 

 Japan. Inö began his geographical survey of Japan in 1800 A. D. 

 and finished it in 1818. 



In 18G0 Mr. Arai, the present superintendent of the Meteoro- 

 loo^ical Office, measured the maunetic declination at a localitv in 

 Yedo (nijw Tokyo) and found it to be 3° 11' AVest. In 18<S:^ a 

 second determination by the same gentleman gave the value 4° 24.' W . 

 From these two determinations we find by a simple calculation 

 that the mean secular variation of manMietic declination during 

 the interval was 3'. 3 per annum. If we assume this rate to hold 

 throughout the century we find, on reckoning either from 1882 

 or 1860, that the year <jf zero dechnation was 1802. This year falls 

 within the ])eriod during which Inö made his survev ; and the 

 concordance between the \arious observations is, to say the least, 

 strikin"'. 



a 



In 1880, Mr. Otto Schutt of the Geological Survey Department 

 made a series of observations (jf all the elements at certain stations 

 in the south easterly part of Ja]) in.* His furrliest north-west point 



* " FAn Bvitnuj zur Kenntni^s der Magnetischen Eni Kraft'' imhlished in the Mittheiluiiijen 

 der Deut>>clien Gesellschaft für Natur und Völkerkunde Ostasiens (22tüs Hest. 1880). 



