ox THE EAUTHUUAKE AND VOLCANIC I'lIENOMENA OF JAPAN. 



the sensitising screw in the bed plate, the pitch of the screw being 1 mm. 

 One complete turn of the screw attached to A tilted the bed plate of this 

 instrument through an angle of 1 in 228. For E and F one complete turn 

 represented an angle of 1 in 222. 



The ratio of unity to the numbers in the second and fourth columns is 

 the tangent of the angle corresponding to a deflection of the boom through 

 a distance of 1 mm., the values of these angles expressed in seconds of arc 



being given in the third and fifth columns. 



E and F 



To bring the points of E or F to the centre of the scale, a rough 

 adjustment is made with the sensitising screw, after which the boom may 

 be slightly moved to the right or left by means of a stone about 40 lb. in 

 weiglit which I shift on the floor of the chamber towards or away from 

 the instrument. 



(/(.) DaiJij Tiltincj. 



The approximate times at which the diurnal wave reached its maxi- 

 mum and minimum, and the amplitudes of these waves for dates between 

 January 24 and March 1, 1894, are given in the table, p. 97. Should it be 

 necessary the table may be completed from December 9, 1893, up to the 

 middle of June 1894. With but few interruptions the records have been 

 continuous. It will be observed that the records for F, which is parallel to 

 A, are only one or two in number. The letter s means that the diurnal wave 

 is too small to be measurable, while blank spaces indicate that it was not 

 visible, the photographic trace being a straight line. Had greater sensi- 

 bility been given to F it is quite possible that the daily wave would have been 

 recorded ; but this could not be done because, even with the stability it 

 had during three days, the end of the boom often wandei-ed through a dis- 

 tance greater than 1 inch, and the spot of light left the fllm. This wander- 

 ing of the pendulums has been already referred to. On two occasions when 

 F gave measurable waves (January 31 and February 2) the times of their 

 occurrence approximately coincided with the movements of Eand A — that 

 is, the movement of the pendulums in one direction was reached in the 

 evening, after which they gradually returned to reach their normal position 

 in the morning. The pendulums E and A, although at right angles to 

 each other, have shown a marked synchronism in their movements. It 

 would seem that these two instruments have either been simultaneously 

 acted upon by independent forces, or that tliey have recorded components 

 of a common force, which has acted in ditt'erent directions at the two 

 stations. 



The latter explanation appears to be the more satisfactory, because 



