776 SEC. 15. GEOGRAPHY. 



Steering Compass, by Sir William Snow Harris (about 

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



Preston's Liquid Compass. A steering compass ; same 

 construction as Dent's without air chamber. 



Dent's Axis Compass (Patent 1844). Card with four heavy 

 and deep needles, attached to axis working in socket above and 

 below, preserving card parallel to surface. 



Steering Compass, by Captain Walker, R.N. Card with 

 single needle, centre of gravity below point of suspension ; pivot 

 long and on a brass bell-shaped cap, the latter cap working also 

 on a pivot. 



Grey's Vertical Compass (Patent 1854). Liquid between 

 outer and inner bowls; card with two dipping needles; pivot 

 inverted. 



Rowland's Liquid Compass (Patent 1854). Eim of card 

 vertical ; pair of needles ; pivot inverted. 



Compass by Mr. Keen (Patent 1854). Porcelain bowl; card 

 two single needles pivot on springs inverted ; cap centred in 

 india rubber ring. 



Magnets used in correcting ship's compasses. Hardsteel ; 

 6 inch ; 10 inch ; and 12 inch. 



SPECIMENS OF THREE DIFFERENT SIZES (4-iNCH, G-INCH, 8 -INCH, 

 IO-INCH) OF MARINER'S COMPASS, WITH SUN AND STAR 

 AZIMUTH MIRROR, AND BINNACLE CONTAINING CORRECTORS 

 FOR QUADRANTAL SEMICIRCULAR AND HEELING ERRORS. 



Sir William Thomson. 



3145b. I. Binnacle, with correctors for quadrantal semi- 

 circular and heeling errors, with mirror azimuth instrument on 

 bowl, for taking bearings of sun, stars, or terrestrial objects. Small 

 size compass (4-inch card), suitable for armour-clads or other ships, 

 with quadrantal error exceeding 1 1. 



3145c. II. 6-inch Compass Card, suitable when quad- 

 rantal error is from 7 to 11. 



3145d. III. Medium size (8-inch card) suitable for 

 standard or steering compass in any ship, iron or wooden, steam or 

 sailing, having quadrantal error less than 7. 



