IV. COMPASSES, 651 



Sledge Compass. Used in Franklin's search-expedition 

 (1850-53). 



Card with single needle capable of being moved round under the card, 

 according to the magnetic variation, so that the North on the card coincides 

 with the true North. A light needle in case attached to shoulder strap, for 

 use without card when the horizontal force is weak. Spare card in cover, 

 and directions for use. 



Sledge Compass, as furnished to Arctic expedition (1875). 



Card with single rteedle capable of being adjusted to the meridian. Aper- 

 ture in leather, so that line of direction may be seen without opening cover. 

 Ivory lifter. 



Small Azimuth Compass, as furnished to Arctic expedition 

 (1875). For determining the variation of the compass. 



Single needle ; alloy pivot ; ruby cap ; graduated circle of alumina metal ; 

 sight-vane, and prism. 



3151b. MARINERS' COMPASSES OF VARIOUS 

 DATES AND PATTERNS : GENERALLY OBSOLETE. 



EXHIBITED BY THE ADMIRALTY HYDROGRAPHIC DEPARTMENT. 



Chinese Compass. Very small needle resting on steel pivot ; 

 cover of talc. 



Walker's Meridional Compass ; with apparatus for deter- 

 mining the latitude when the sun is on the meridian, also the sun's 

 altitude, and hour angle. 



Crow's Liquid Compass (Patent 1813). 



Card hollow, convex lens shaped, buoyant and pressing upwards against the 

 pivot. Expansion of liquid provided for by air chamber round upper rim of 

 bowl ; also by a spring valve allowing the escape of expended air and refilling 

 when required. In the original patent the liquid was entirely alcohol. 



Pope's Dipping Needle Compass (Patent 1820) ; with 

 arc showing dip of the needle. 



Gray don's Celestial Compass (Patent 1824) ; with appara- 

 tus for determining the latitude, the angular distance between 

 celestial objects, and their true azimuth. 



Danish Azimuth Compass ; with telescope for observing 

 distant bearings. 



Steering Compass, by Sir William Snow Harris ' (about 

 1831) ; with stout copper ring, to calm vibrations of needle. 



