32 Mr. Sidney G. Brown [Ja n - BO, 



weight. As the Bhip changes its speed the acceleration will act upon 

 the pendulous weight and cause an oscillation to be started. This 

 oscillation is termed the " Ballistic Deflection." 



The permanent north steaming error and the transitory error, 

 due to the ballistic deflection, are in the same direction, and mathe- 

 maticians have calculated that with an undamped Gyro-Compass, if 

 the time of its oscillation is set to 85 minutes in any particular 

 latitude, the ballistic deflection can be made exactly the same as the 

 deflection due to the north steaming error ; this being so, the 

 compass should move into its new resting place without further 

 oscillation. 



This would be true if, as before indicated, the compass was 

 undamped in its swings ; but the mathematicians have overlooked 

 the fact that all Gyro-Compasses are damped, and the ballistic de- 

 flection must, therefore, include a term due to the damping. 



This damping term up to the present has been neglected ; but 

 in practice it is found that when a ship is steaming and turning to 

 alter its course, the compass does not come deadbeat to its new 

 position, but has an oscillation started which is common to all 

 existing Gyro-Compasses. The extent of this oscillation may be 

 termed the " Damping Error." 



On a merchant ship the damping error is of little moment ; but 

 on a war vessel which is manoeuvring it may be serious, as it may 

 swing the compass off its correct reading by several degrees. 



I have made certain modifications in my compass to remove the 

 damping error, but will not explain my method as it has not yet 

 been tested in practice. 



I have drawn attention to several faults that have to be rectified 

 if the compass is to be of use on a ship, and I shall now discuss the 

 last, but by no means the least, of the errors that may arise if the 

 instrument is not properly designed. 



This error was not known when the Gyro-Compass was first 

 brought out ; it proved a most difficult fault to correct, and its 

 elimination has had more to do with the design of the later forms of 

 tiyro-Conipasses than any other factor. 



If a gyro wheel is precessed towards and kept pointing to the 

 north by an ordinary pendulum weight it will work well on board 

 ship, provided that the ship is steaming on a fairly smooth sea ; but 

 if the direction of the compass points anywhere in the quadrants — 

 that is. N.W. or N.E., S.AV. or S.E.— and the ship rolls, the wheel 

 will try to set itself so as to bring the rim of the spinning wheel in 

 line with the roll, and in a long continued and heavy roll the com- 

 inay show an error of twenty or more degrees, a most serious 

 fault, and one that would render the instrument quite useless in a 

 heavy sea. This error is called the " Quadrantal Error." 



The extent of the error depends upon the violence of the ship's 

 rolling and the direction of the axis of the wheel. 



