226 KNOTT AND TANAKADATE 



The method of comparison was the shnplest that could be 

 imagined. Sekino's vahies of the maofnetic elements at any station 

 were subtracted from the corresponding values obtained on the present 

 Survey. This gave a series of differences for each set of elements. 

 The algebraic sum of these differences may then be assumed to give 

 some hint as to the existence, at any rate, of a secular variation. 



As regards the Dip there is a distinct tendency for the differences 

 to be negative. That is, our values are on the whole smaller than 

 Sekino's. Thus, out of the 27 Stations, there are only four, for 

 which our values of the dip are greater than his. Dividing the alge- 

 braic sum of all the differences by the number of stations we get for 

 the average difference —8'. 8 or — 7'.0, according as we include or 

 neglect Hakodate, for ^Yhich the difference ( as much as — 1°10'.4) 

 is peculiarly large. We may therefore regard this — 7'.0 as an indi- 

 cation that the dip is subject to an annual diminution of about 2' per 

 year. This does not agree with the results of the observations made 

 at the Naval Observatory,* which hint rather at a rate of increase. 



As regards the Horizontal Forces, again, there is a marked ten- 

 dency for the differences to be positive, six only out of the twenty- 

 seven beinir neofative. The mean difference is + .00091 ; or, in other 

 words, our values are greater than Sekinos by fully one-third per cent. 

 This means an annual rate of increase of .00023. This result is in 

 agreement with the result already indicated by the observations made 

 at the Naval Observatory. 



The differences obtained by a comparison (^f the Total Forces are 

 very nearly as often positive as negative. The general drift, however, 

 is in the negative direction ; so that the Total Force seems to be 

 subject to a mean diminution of —.00012 per year. 



* As this paper was passing through the press, this Observatory was incorporated with 

 the University, and is now known as the Tokyo Observatory. 



