280 POPULAR LECTURES AND ADDRESSES. 



" being attached to a proper stand, or ' binnacle/ 

 " fixed in the ship ; thus the bowl levels itself to 

 " the plane of the horizon though the ship is tossed 

 " about in various directions by the waves. 



" The needles are either two with their ends 

 " brought together, or one of nearly oval form with 

 " pointed ends, which performs its duty more 

 " surely and swiftly. 1 The attachment of the 

 " needle, or needles, to the card circle is such that 

 " its centre is in the middle of the magnetic iron ; 

 " but, on account of the variation of the compass 

 " from the meridian, artificers in different regions 

 " and cities connect in different ways the needles 

 " to the card in respect to their directions re- 

 " latively to the thirty-two points. The first pre- 



1 This opinion of Gilbert's is not borne out by advanced know- 

 ledge of the laws of magnetization, which show that the oval ring 

 needle cannot be trusted to for keeping its magnetic axis securely 

 in a constant direction under whatever disturbing influence it may 

 be subjected to, as does a thin rod or bar. The oval form was 

 authoritatively condemned on this account by the British Admiralty 

 Committee of 1837, who found the theoretical objection amply 

 confirmed by experience. They actually found compasses of this 

 pattern, which had been in use for some time at sea, presenting 

 errors of as much as three degrees on account of the displacement 

 of the magnetization in the substance of the needle. 



