54 BEXJ. PIKE'S, JR., DESCRIPTIVE CATALOGUE. 



outer one being fixed by horizontal points, both to the inner 

 circle which carries the compass box, and also to the outer 

 box ; and the two sets of axes being in directions at right 

 angles to one another, by the combinations of movements 

 determined by these axes, the inner circle, with the compass 

 box and its contents, always retains a horizontal position dur- 

 ing the rolling of the ship ; and the pilot, by looking at the 

 position of the needle, can steer his course in any required 

 direction. Although the north pole of the magnet, in every 

 part of the world, when freely suspended, points to the 

 northern parts, and the south pole to the southern parts, 

 yet its ends seldom point exactly towards the poles of the 

 earth. The angle in which it deviates from due north and 

 south is called the angle of declination, or the variation of 

 the compass ; and this declination is said to be east or west, 

 according as the north pole of the needle is eastward or 

 westward of the astronomical meridian of the place. This 

 deviation from the meridian is not the same in all parts of 

 the world, but is different in different places, and it is even 

 continually varying in the same place ; the present declina- 

 tion of the needle is 



Price, with wood bowl, $2.50. 

 Fj g- 87 " " brass " $4.50. 



Brass Boat Compass. (Fig. 87.) The brass 

 boat compass with nautical floating card. 



Price, 2 inch diameter, $2.25. 

 " 3" " " $2.75. 



The Azimuth Compass. (Fig. 88, page 55.) The azi- 

 Aiuth compass differs from the ordinary mariner's compass, 

 only in the circumference of its inner box being provided 

 with sights, through which any object, either in the horizon 

 or above it, may be seen, and its bearings from the magnetic 

 points of the compass determined, by reference to the posi- 

 tion of the card, with respect to the sights. For this pur- 

 pose the whole box is hung in detached gimbals, which 

 turn on a strong vertical pin fixed below the box, which is 

 thus capable of being moved around horizontally, and of 

 the sights being directed to whatever object is to be viewed 

 through them. On one side of the box there is usually 

 inserted a nut, or stop, which, when pushed in, presses 

 against the card and stops it ; this is done to enable the 



