292 POPULAR LECTURES AND ADDRESSES. 



disturbed, but the disturbance due to this cause, 

 except in a very small vessel, is scarcely 

 perceptible. 



There is also another cause of unsteadiness in 

 which the rolling of the ship produces oscillations 

 of the compass, and that is through what is called 

 the heeling error. When the ship is inclined over 

 to one side or other, the compass experiences a 

 deflecting magnetic force tending to cause it to 

 point in a different direction from that in which it 

 points when the ship is upright. This influence, 

 which sometimes amounts to as much as two 

 degrees for every degree of heel, is, in many cases 

 a more potent cause of unsteadiness than the 

 merely dynamical influence of the ship's rolling ; 

 and it is thus remarkable that, in many cases, the 

 two influences conspire, each tending to draw, in the 

 northern hemisphere, the north point of the compass 

 card, and in the southern hemisphere, the south point 

 of the compass card, to the upper side of the ship 

 with maximum force when the inclination is a 

 maximum ; and each is greatest when the ship's 

 head is north or south, and nearly evanescent 



