1920] on The Gyrostatic Compass 33 



If the compass points direct N., S., E., or W. the error is nothing, 

 but it would be a maximum in any of the directions before mentioned. 



I think Anschutz was the first to point out the error and suggest 

 a cure ; this I gather from one of his publications in the year 1911, 

 in which, speaking of the tendency of the compass to wander when 

 on board ship, he says : — 



" Theoretically the influence of rhythmic turning movements on 

 a gyroscopic apparatus must disappear completely if not only the 

 real, but also the apparent moments of inertia of the movable system 

 become equal for each plane." 



If we go back again and study our simple Gyro-Compass, we .see 

 that the movable system is not symmetrical. In the direction of the 

 axis of the wheel the effect of tilting movement is more or less 

 resisted by the spinning wheel ; this may be termed the stabilized 

 direction, while at right angles to this — that is, in the direction of 

 the rim of the wheel — there is no resistance to tilting encountered, 

 and this direction we term the direction of free swing. 



A simple form of Gyro-Compass pointing therefore in a direction, 

 say, N.W. on board a rolling ship, has a force applied to it tending 

 to turn it so as to bring its direction of free swing into line with 

 the roll. 



Anschutz gets rid of the error by multiplying the number of his 

 gyro wheels, and by constructing the instrument as symmetrical as 

 possible. 



In England the quadrantal error was first discovered and studied, 

 I believe, by the Admiralty Compass Department. 



In the year 1914 the Sperry Co. claimed to have effected a cure 

 for the error by attaching the pendulous weight, not directly to the 

 gyro casing, but through a pin arranged to move in a slot in 

 the casing. 



In order that the axis of suspension of the pendulum may remain 

 vertical when the compass oscillates with the rolling of the ship, a 

 small auxiliary gyro was employed to stabilize the pin connection 

 between the pendulum and the gyro casing. 



We therefore see in these applications of Anschntz and Sperry 

 two general ideas. 



In the first case the idea is to make everything symmetrical, like 

 a ball, so that there is no stabilized or free swing direction to the 

 wheel, and therefore no tendency to turn ; while in the second case 

 a method is provided to prevent the point of application of the 

 pendulum weight from moving, and acting as a crank, and by 

 keeping the pendulum weight always vertical in the X.AV. direction 

 to destroy its power of turning the compass. 



In the " Brown " Compass the quadrantal error is eliminated by 

 making the weight operate completely out of phase with the roll — 

 that is, at 90° displacement. 



If a Gyro-Compass is worked by a weight which tends to precess 



Vol. XXIII. (No. 114) d 



