MAGNETIC SURVEY OF JAPAN. 



!<;■ 



npproxiniate corrections so as to reduce our results to ouc epocli. 



We had hoped ])ef()re starting to have had the cooperation of 

 the observers at the Naval Observatory, where for some years fairly 

 systematic measurements of the magnetic elements have been made. 

 Since 1883, the declination has been taken rec^iilarlv everv dav at 

 7 a.m. — not a very good hour if probability of steady values or of 

 good means is aimed at. The Horizontal Force and Dip have been 

 taken each twice a month, the former alwavs in the afternoon between 

 2 p. m. and 5 p. m.. and the latter usually immediately thereafter, 

 excepting on ;i few occasions when it was observed in the morning. 

 The Horizontal Force was measured with the Deflectinsf jMasfnet at 

 one distance only. The mean values for the years 1885-6-7 are given 

 here, being calculated from the tables published in the Annual Reports 

 of the Naval Observatory. The Horizontal Force was measured in 

 foot- grain -second units ; but the values are here reduced for con- 

 venience to the centimetre-îjramme-sccond units. 



All show evidence of an annual rate of increase, ll will be 

 noticed more especially that the annual rate of change of Declination 

 is much smaller (about l'.ö) than the value deduced from Inö's and 

 Aral's observations. 



Another fact deducible from the Naval Observatory Reports is 

 that, so far as can be judged from the limited number of observations 

 made, the magnetic conditions diu-ing the summer months of 1887 



