u 



Mr. Sidney G. Brown 



[Jan. 30, 



the wheel in phase with the roll, then there must be a quadrantal 

 error, but there will be no error if it is forced to operate completely 

 out of phase with it. 



When I describe the " Brown " Compass I will explain how this 

 is carried out. 



It is also essential, as Anschutz has remarked, that the real 

 moments of inertia shall be the same in all directions of the movable 

 system of the compass — that is to say, the moving system should be 

 in dynamic balance, as it is termed. 



If a child's hoop is suspended by a string and is swinging in one 

 direction, the hoop tends to set itself lengthwise to the direction of 

 the swing. On the other hand, if an exactly similar hoop is placed 



Fig. 7. 



over but at right angles to the first, and suspended as before, then on 

 swinging the hoops there will be no tendency for them to turn, as 

 they are now in dynamic balance. 



It is for this reason that the mass distribution of the moving 

 system of the Gyro-Compass should be in dynamic balance, and to 

 carry this out adjustable weights are fitted, usually in the direction 

 of the spindle of the wheel, to counteract the weight of the support- 

 ing ring i n the gyro casing, and thus there is no tendency for the 

 compass to turn, due to this cause, when under the action of rolling. 



