CHAPTER V. 



SHIP'S MAGNETISM AND THE COMPENSATION OF THE COMPASS.* 



63. The ship's compass. The style of ship's compass which 

 is now almost universally used is that which is due to Lord 

 Kelvin. The card of this compass is shown in Fig. 69. The 



Fig. 69. 



points of the compass and the circle divisions are printed on 

 a paper ring to which is attached a light rim of aluminum which 

 keeps it in shape. Radial threads connect the paper ring to 

 a central disk which contains a sapphire cap by which the com- 

 pass is supported on an iridium point. Eight small magnets of 

 glass-hard steel are tied to the radial threads four on either side 



* A good discussion of this subject is given in Gray's Treatise on Magnetism and 

 Electricity, Vol. i, pages 85-100, Macmillan and Company, 1898. For full details, 

 the reader is referred to Lord Kelvin's Instructions for Adjusting the Compass, to 

 be obtained from James White, of Glasgow. The practice in the United States 

 Navy concerning the matter of compass errors and compass adjustments is given in 

 several small pamphlets which are published by the United States Navy Depart- 

 ment, and in a book entitled A Treatise on Navigation, by Commander W. C. P. 

 Muir, U. S. Navy, Annapolis, 1906. The practice in the British Navy is given 

 in the Admiralty Manual of Deviations of the Compass. 



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