THE GYROSCOPE FOR MARINE PURPOSES. 149 



Other operating the precessional ring through an intermediate miter seg- 

 ment. This arrangement affords means whereby either of these rings may 

 be tilted at will by the simple act of drawing the cord through the center 

 of the gudgeons, and round either one or the other of the pulleys. No 

 movement, manipulation or stress whatsoever applied to the cord, could 

 in any way affect the oscillation of the pendulum for the reason just stated 

 that the cord passes through the center or axis of this oscillation, and in 

 line therewith. 



It will be observed, in operating this model, that the gyroscope itself 

 fails to respond to all the smaller angles. It responds freely to the large 

 ones or wide angle oscillations, but either does not respond at all or moves 

 very slightly with the smaller oscillations as stated. Not responding, it 

 cannot, of course, control or extinguish these smaller oscillations. It being 

 desired, especially in connection with improvement in conditions for gunnery 

 on battleships and war vessels generally, that the gunner should operate if 

 possible from a level gun platform, it therefore becomes desirable to 

 act on these smaller oscillations of roll of the ship so as to completely 

 extinguish them and hold the ship on a practically even beam. This 

 especially as now all the larger war vessels are designed for broadside 

 service and volley fire. The gunner therefore is compelled to keep an 

 absolutely true and incessant aim upon the target. If the ship is rolling 

 much or little this is a more difficult task. Again the recoil of the volley fire 

 throws the boat over and sets up rolling, and it is the duty of the gyroscope 

 to extinguish and prevent all rolling disturbances, from whatever source. 

 As we have seen, the lesser angle rolling cannot be taken care of by the 

 passive type of gyroscope. We must rely upon the active type. By this 

 means the full angle operation of the gyroscope is secured where necessary, 

 independently of the amount of motion or, in fact, any motion whatever 

 on the part 'of the ship, and is therefore in readiness to deliver to the boat 

 stresses which are equal and opposite to those received by the boat from 

 any source and prevent them from causing the boat to roll. 



It is interesting to note that when the boat is held free from motion, 

 as by the delivery of stresses equal and opposite to balance the wave effort, 

 no power is required to actuate the gyroscope other than to overcome inertia 

 and friction, which is almost negligible. When the roll is being suppressed 

 and the boat is moving then the boat is doing work upon the gyroscope, 

 and it then becomes the province of the actuator to emplace the oscillations 

 of the gyro properly with reference to those of the boat, and at such angular 

 velocity as to best suit the conditions, structure and mountings. 



The work of Sir John I. Thornycroft for preventing rolling, and his 



