ON THE EARTHQUAKE AND VOLCANIC PHENOMENA OF JAPAN. 117 



one degree. The pitch of a screw was one millimetre, and its distance 

 from the axis on which the bed plate was tilted may be taken at 220 

 millimetres. All the instruments excepting A had usually a sensibility 

 of 1° for 3 mm., which is approximately equal to a tilting of 1" for each 

 millimetre of deflection. Occasionally the sensibility was increased two- 

 fold or threefold. The reason for this indefiniteness respecting sensibility 

 is that the notes relating to the calibration of the instruments were burned. 

 The chief value of these determinations is to give angular values for the 

 diurnal wave, and because it will be shown that this is a quantity with 

 large variations depending upon locality and weather, the necessity of 

 accurate measurements becomes more apparent than real. 



The Pendulum at A. — Sensibility, September 26, 1894. 1°:=12 mm. 

 or 1 mm.=:0""20. This instrument, which was adjusted to have a sensi- 

 bility twice or six times greater than the other instruments, was installed 

 in my private observatory on a massive well-built stone column resting 

 upon a bed of concrete. Towards the east and west it was protected by 

 60 feet of building, but to the north and south by only about lOfeet. The 

 only window in the room, whicli was on the south side, was always closed 

 by a curtain on the inside and a solid shutter upon the outside. The 

 reason that it was oriented to record N.E. and S.W. motions was because, 

 as was explained in the last Report, there were reasons for believing that 

 in such a direction earthquake and other motion had a maximum. The 

 daily movements were often eclipsed or made indefinite by the occurrence 

 of tremors. When they were visible, although on one occasion they were 

 represented by deviations of 8 mm., it was rarely that they exceeded 2 or 

 3 mm. In many instances it seems that a second wave was superimposed 

 upon the ordinary diurnal disturbance. Excursions towards the N.E. were 

 usually completed between 5 and 15 hours, Avhile the S.W. motion ended 

 between and 3 hours (tig. 6, p. 134). 



Pendulums at C and D. — These were installed upon rock in a ca\e at 

 Kamakura, about 27 miles distant from the pendulums in Tokio. One of 

 these recorded motion in the direction of the dip of the strata, and the 

 other in a direction at right angles to this. Their records are described 

 in the Report for 1893-94. 



Pendtdums at E and F. — These pendulums were in directions N.E. 

 and N.AV. or parallel to C and D. The N.W. booms were parallel to A. 

 The installation was iu an underground chamber, where as at Kamakura 

 the daily change in temperature was practically unappreciable. These 

 records are described in the Report for 1893-94. 



Pendidums at G and II. — The pendulums G and H were placed on the 

 rock in a cave at the Yokohama Brewery. Their orientation corresponded 

 to that of C and D or E and F, and their records are referred to in the 

 above-mentioned Report. 



Pendidivm at I. — This pendulum was in an exceedingly damp cave 

 at Kanagawa, about three miles distant from G and H. Its boom, like 

 that of A, pointed towards the north-west. The few records obtained 

 from this station are described with those of the above-mentioned three 

 stations. 



The Pendulum at J. — Sensibility, August 18, 1894, 1° = 6"5 mm., 

 or 1 mm. = 0"-39. January 5, 1895, 1°=3 mm., or 1 mm. = 0"-80. 



This was an aluminium boom which, with its plate and index, had a 

 total length of about 4 feet 9 inches. Its cast-iron stand rested upon a 

 slab of slate upon the top of a short brick column, which rose from a layer 



