— 11 — 



OGASAWARAJDIA. 



Date axd Time. 



H 



Magxet. 



Obsekvee. 



Anenst 15th 4 P.JI 



.3198 

 .3133 

 .3184 

 .3155 

 .3177 

 .3164 

 .3154 

 .3199 

 .3129 

 3169 



B 

 D 

 C 

 A 

 B 

 A 

 D 

 C 

 D 



K 



S 

 S 

 S 

 S 

 H 

 S 

 H 

 S 

 8 

 S 





Anffust 16th Q\ A.M 



IJP-M 



August 17th 8JA.M 



2 P.M 



Q 



31 





lu 





1 



Mevn 



3166 1 









II 



DECLINATION. 



Declination experiments were carried out by means of 'an electro-mag- 

 netic declinometer (see Fig. 2). This instrument essentially consists of three 

 parts, a theodolite, a coil, and a magnetometer. 



The theodolite is one of the ordinary kind, and forms the base of the 

 instrument. Its azimuth-circle reads to 5." 



The coil* is wound on a rectangular bronze frame in two parts with an 

 open space in the center. The hollow pivots are of the same diameter as 

 those of the theodolite telescope and project at right angles to the axis of the 

 coil, which is disposed symmetrically about their line of collimation. Two 

 narrow slits in the middle of the ends of the coil approximately define the 

 median plane of the coil. About 700 turns of a fine insulated copper wire are 

 wound in this frame in two layers, and the ends of the wire are led off from 

 the same point in the coil. The two leading wires are twisted together 

 and terminate in a twin-plug. In order to prevent tho leading wires from 

 being easily cut they are tied to the frame by an elastic string. The total 

 weight of the coil approximately equals that of the telescope belonging to the 

 theodolite. 



The magnetometer is an ordinary small reflecting ono. It stands upon 

 an independent tripod nearly centred with the theodolito and projects through 

 the open space in the center of the coil. A small mirror magnet is suspended 



• For the discussion of tho proper proportion of the sliapc ot the coil «ec Proc. R. S. E. 

 Vol. Xll (1883-4). 



