MAGXETIC SIKVEY OF JAPAN. 



17Ô 



The rravelliiig was usiialJy eitectod by ineaus ol" jinrikishu ; and 

 there cannot l)e the least doubt that the rattling and jolting did not 

 increase the steadiness (jf the chronometer. Frequent sextant obser- 

 vations were therefore absokitely necessary, so that a fairly accurate 

 value of the mean daily rate could be obtained. Then^ always must 

 be, however, a certain doubt as to whether the mean rate so obtained 

 is really the true rate when the chronometer is resting. It is highly 

 probable, in fact, that irregularities must resuh from sufh a j'oJting as 

 jinriküha give : we can only hope that these irregularities balance each 

 other in the long run. 



The results obtained will be discussed along with the observations 

 of the Southern Party. Their mode of operating was in many details 

 quite different from the mode adopted by the Northern Party, and 

 calls for a full account both of instrimients and methods. 



The following account is drawn up, almost in his very words, 

 from Mr. Tanakadate's own descriptive notes. 



Section III. 



With the Exception of the theodolite, which was fitted up both 

 for transit and for magnetometric observations, the South Party 

 resembled the North Party in its equipment. A chronometer, (Negus 

 Sidereal, 1629), a dip circle, a box of tools and necessary books, and 

 a tent, completed the out -fit. 



The dip and vibration Experiments were always carried out by 

 Mr. Imagawa ; wdiile Mr. Tanakadate undertook the chronometei- 

 rating, and the declination and defiection experiments. Usually the 

 one acted clerk to the other, noting down what the latter read otf. 

 In the vibration experiments, the observer signalled the vibrations. 

 and the instants of signal were timed by Mr. Tanakadate from the 

 chronometer and noted down. In the transit-observations, however. 



