18 HEYL & BRIGGS— THE EARTH INDUCTOR COMPASS. 



If the sine brushes only are connected to the galvanometer, its 

 reading will be zero only when the vessel lies in the magnetic merid- 

 ian ; and if the cosine brushes only are connected, the reading will be 

 zero only in a magnetic east and west line. 



Fl'q.Z 



4C 



Figf-. 



-s 



We may connect the two pairs of brushes in series so that the 

 voltage applied to the galvanometer is sin 9 -{- cos 9. This function 

 will be zero only when ^=135° or — 45° ; that is, when the vessel 

 lies in a northwest and southeast line. And if we use the combination 

 sin 9 — cos 9, this will be zero when ^ = 45° or 225°; that is, in a 

 northeast and southwest line. 



