184 



KNOTT AND TANAKADATE 



sn'ôw 5, and so leavino; the dnmnar to lianof freelv. It is for this reason 

 indeed that tlie fan-shaped body, d, is called jjy tliat name. For, in 

 virtue of its sjiape, it very speedil\" r-onies to aj)proxi]nate rest as it 

 swings in the small space between the bell-glass and the shelf, and of 

 course comes to final rest only when all twist has Ijeen taken out of 

 the spider line. Tf the suspension is left for a few hours in this posi- 

 tion, say overnight, Ave are safe in assuming that the twist has been 

 ])racti('ally elimimited. A slight tip will now bring the handle of the 

 «lainper into the notch, where it is securely clamped by screwing the 

 screw h home. The magnet<^meter, when placed erect, is now ready 

 for use. This magnetometer is an essential part of the a])pnratus 

 required both for the declination and deflection experiments. The 

 Declinometer will now be described. 



The peculiar feature of the electromagnetic declinometer is a 

 coil of wire of a convenient form, whose axis can by a simple ex- 

 perimentMl method be accurately made to coincide with the magnetic 

 meridian. The coil is shown in Plate W. Fig. 1, and also in the 

 annexed cut. It is wound on a 

 flat rectario-idar frame of brass in 



Fig. 2. 



(^ natural size), 



two separate parts, a certain por- 

 tion in the middle being left 

 vacant. Looked at from above, 

 it is srpiare. Two pivots pp 

 project from the middle of the 

 sides in a direction perpendicular 

 to the axis of the coil. These pivots are hollow, and ai*e made of 

 the same external diameter as those of the telescope belonging to the 

 Iheodolite. The upper and lower surfaces are pierced so as to allow 

 the magnetometer to project above the coil. The middle part of the 

 frame where no wire is coiled is equal to the height of the frame and 



