36 Mr. Sidney G. Brown [Jan. 30. 



The gyro wheel runs at 15,000 revolution per minute, and thus 

 acts as a powerful blower, giving- an air-pressure equal to some 

 3 inches of water. 



Fixed to the vertical ring, but connected through the hollow 

 bearing m to the inside of the case, is the air jet L. This jet blows 

 into the two halves of the air box K, and thence through the 

 pipes J. The air-pressure is thus transmitted to the oil in the two 

 sets of bottles C and D. 



H is another air jet similarly mounted and employed to act upon 

 a pair of contact-making vanes I. 



The contacts I, through the agency of the controller which is 

 fixed on the switch-board, is to work the repeaters and the step-by- 

 step motor Y. This motor forces round the follow-up ring N to 

 keep the contact-making vanes I always opposite the air jet, and in 

 doing this all the repeaters on the ship follow suit. 



U is the compass card fixed to the upper portion of the vertical 

 ring, and is the lubber line support. 



By removing the four screws marked n the Gyro-Compass can be 

 completely removed from the gymbal rings. 



The instrument thus removed is shown in Fig. 5. 



To explain the action of the oil bottles I have introduced the 

 Figs. 9 and 10. 



Fig. 7 illustrates the simplest form of compass, in which the 

 wheel and case B are controlled by the pendulous weight W. 



When the case tilts as shown, W is moved to one side of the 

 vertical support, and the weight tries to bring the case again to the 

 horizontal. 



Suppose the wheel revolves in the direction of arrow a, the righting 

 torque is in the direction of arrow b, then the wheel and case will turn 

 in azimuth in the direction of the arrow e. 



Such a compass would have a quadrantal error, because the weight 

 W would produce stresses in phase with the roll. 



Fig. illustrates the method of control of the "Brown" compass. 

 When the case B is horizontal, the bottles EE are half full of oil, 

 and the air jet L is blowing equally into the two halves of the air 

 box K ; but when the case tilts as shown, then the air pressure blows 

 into one side of the box more than the other, and in such a direction 

 as to force the oil from the lower bottle into the one raised. There 

 is, therefore, a considerable righting torque indicated by the weight 

 of the oil W trying to restore the case back again to the horizontal. 



When the pendulum swings under the action of the rolls of the 

 ship, the air jet L moves from one side to the other side of the air 

 box in tune with the roll, blowing the oil periodically from one bottle 

 to the other. At the middle of the swing of the pendulum the air 

 jet is at the middle of the air box, and there is no difference of air 

 pressure, and therefore no movement of the oil ; and when the swing- 

 is at the end of its path and not moving, the air jet is at one side of 



