288 THE SPERRY GYRO-COMPASS IN SERVICE. 



the time taken by all classes of vessels to accelerate from one speed to another. 

 From this data the acceleration pressures were calculated and actually 

 applied to the experimental instrument by means of weights allowed to act 

 for a certain length of time. 



The manner in which all of these problems were solved and the strong 

 and accurate instrument which is the result can best be explained by reference 

 to Fig. I, Plate loi, which is a part section in the plane of the gyro wheel. 

 The wheel itself rotates on the axis A , which is carried in a special type of ball 

 bearing in the casing B. Casing B is in turn carried on the horizontal axis 

 C in the ring D, which is called the vertical cardan ring. The vertical ring 

 D is suspended by the stranded wire E and is guided about the vertical axis 

 by the steadying bearings F-F. The top of this suspension wire is held in a 

 frame which surrounds the sensitive element. Attached to this frame and 

 integral with it is a ring G which surrounds the vertical cardan ring. This 

 is termed the "phantom" ring because it is made to follow all tendencies of 

 the cardan ring to move about the vertical axis. This upper frame, which 

 surrounds the sensitive element, is mounted to swing in gimbal rings in the 

 manner that is familiar in connection with magnetic compasses. Attached 

 to the vertical cardan ring, and projecting through holes in the phantom ring, 

 are posts, not shown in the figure. On these posts are carried small silver 

 wheels which rest on a flat commutator carried in the movable frame of the 

 compass, of which the phantom ring and suspension head are integral parts. 

 This commutator has two silver segments insulated from each other by a 

 narrow piece of mica. When the frame and sensitive element are both at 

 rest, the silver trolley wheels attached to the posts on the vertical cardan 

 ring rest on both of these silver segments, thus energizing both sides of the 

 relay controlling the movements of the azimuth motor M, the purpose of 

 which is to drive the frame about the vertical axis. If the gyro tends to 

 move about the vertical axis these trolleys are moved ofif the insulating seg- 

 ment and on one of the silver segments, thus energizing the motor M in such 

 manner as to cause the frame, phantom ring, compass card and repeater 

 transmitter to follow the gyro. It can be seen that the top of the suspension 

 wire is always moving to follow the bottom, so that the wire is virtually 

 torsionless and the suspension frictionless about the vertical axis. 



Swung in trunnions in the phantom ring, and passing through the ver- 

 tical cardan ring but not touching it, is the bail or pendulum R, which is 

 attached to the gyro casing at the point marked S. The vertical cardan ring 

 is of such depth at the bottom as to permit the bail to swing freely through it. 

 The phantom ring is at all times held rigidly in position with reference to the 

 binnacle, although it is at the same time free to move around the vertical axis. 



