26 POPULAR LECTURES AND ADDRESSES. 



an instrument adapted for showing, in a manner 

 most convenient to the mariner, the azimuth of 

 the ship's length relatively to the magnetic north 

 and south line. It consists of a circle of card- 

 board, or of mica coated with paper, marked on 

 its upper side with the points of the compass, or 

 degrees, or both points and degrees, and carrying 

 two or four parallel bars of magnetised steel 

 attached to it below, and an inverted cup of 

 sapphire or ruby, or other hard material, attached 

 to it over a hole in its centre. It is supported 

 by the crown of the cup resting on a hard metal 

 point standing up from the bottom of a hollow 

 case called the compass bowl. The compass bowl 

 is covered with glass to protect the card against 

 wind and weather, and the bowl is hung on 

 gimbals in a binnacle attached to the deck, and 

 bearing convenient appliances for placing lamps 

 to illuminate the card by night. The cheapest 

 and roughest instrument made according to this 

 description provided the bearing cup is of hard 

 enough material and properly shaped, and provided 

 the bearing point is kept sufficiently fine by 



