MAGNETIC SURVEY OF JAPAN. 183 



tube of the magnetometer case, serves as a guiding slot in "which the 

 small toothed piece moves. 'J'he ring nn is milled on the outer 

 surface. When it is turned l)y the finger, tlie toothed piece in gear- 

 in<2r with it rises or falls accordinn^ to the direction of turnino; ; and 

 with it the sliding; tid)e also moves, and opens or closes the vice. 



The mngnetometer case expands below into a disk (//), with a 

 hemispherical knob on its lower surface. This knob rests in a 

 tetrahedral hole cut in the base-plate. l^y screws passing through 

 the disk and bearing on the base plate, the magnetometer case can 

 easily be adjusted to a true verticality. (See Fig. 3, Plate VIT, also 

 Fig. 2, Plate YI). 



To mount the magnet and damper in the case, after they have 

 been connected by the spider-line, the top-cover must first be un- 

 damped and removed. The small screw, h, is uncrewed a little so 

 as to leave the triangular space or notch in the shelf quite open. 

 The top is then held inverted in the one hand ; and with the other 

 the stem a' is carefully lifted until the damper hangs free. The dam- 

 per is then dropped through the slit, the magnet and mirror carefull}- 

 deposited on the table near by, and the screw h tightened so as to jam 

 the "handle" of the fan-shaped damper up against the sides of the 

 notch. The top piece is now held up in its proper position, so that 

 the magnet and mirror hang freely from it. These are next gently 

 lowered into the tube- case of the magnetometer, and the top is clamped 

 in the position which makes the mirror hang level with the circular 

 windows. The stem a' will now hang in its proper position between 

 the arms of the vice, which should be opened before these operations 

 are begun. If the hanging is done carefully by an experienced hand 

 there should be little or no twist on the spider line. Any twist can 

 however be easily removed by gi'ipping the stem below the magnet 

 with the vice, inverting the magnetometer case, unscrewing the small 



