The SPERRY gyro-compass in service. 295 



or dumb compass, to obtain the line of bearing, many errors are introduced 

 by the lag of the compass. As the gyro-compass has no lag whatever, this 

 source of error is entirely eliminated by its use, and line of bearing formations 

 can be kept with great accuracy. 



All repeating compasses used are of the same type and consequently 

 interchangeable. They may be mounted in gimbal rings or on the wall, 

 ceiling or pedestal fixtures provided. Repeaters are illuminated from behind 

 the dial; a small rheostat in circuit with the lamp makes it possible to 

 obtain any desired intensity of illumination. The pelorus repeaters may 

 be very faintly illuminated so that the light from the card will not interfere 

 with obtaining bearings at night ; the helmsman's repeater may be brightly 

 illuminated so that all graduations of the compass card are distinctly visible 

 from the wheel. 



A comment made by one of the navigating officers using the Sperry 

 gyro-compass serves to illustrate another important advantage. This com- 

 ment was to the effect that since using the gyro-compass for navigating the 

 ship he found little if any difference between the position of the ship by dead 

 reckoning and the position by observation. The position by dead reckoning 

 is that calculated from courses and distances run and is the position the ship 

 should be in ; the position by observation is that computed from observations 

 of heavenly bodies or land and is the actual position of the ship. This differ- 

 ence is called "current correction," current being the scapegoat on which the 

 delinquencies of the compass are fastened. In navigating a ship the calcu- 

 lated course is constantly modified as observations show it to be necessary. 

 In other words, the ship is headed as nearly as possible on the proper course, 

 and observations are taken to ascertain how far the ship is out of her course 

 and how the succeeding course should be laid to arrive at the destination. 

 This results in traversing a longer path than necessary, and in consequent 

 loss of time and fuel. In foggy or cloudy weather the ship might get so 

 far out of her course as to put her in a dangerous position. 



With the gyro-compass it will be possible to navigate the ship accurately 

 in any sort of weather and without taking observations to check the posi- 

 tion. Observations would of course be taken in good weather as additional 

 safeguard. 



Navigating officers using the Sperry gyro-compass assert that the 

 compass will entirely pay for itself within a year after its installation by the 

 saving in fuel which will result from the use of an accurate compass having 

 no lag. 



The device heretofore referred to for determining the position of the 

 meridian independently of the compass card has been found of much value 



