222 ACTIVE TYPE OF STABILIZING GYRO. 



will always be met by the maximum mass moment against rolling, whereas a 

 stabilizer based on resonance and itself possessing very large inertia will keep on 

 rolling the ship. 



The inertia of a pendulous damping mass can be destroyed quickly enough, 

 but this should always be done at such a rate as to maintain its period, and its mass 

 must then be re-energized by the ship at the cost of further roUing. 



If we consider a typical roll record, taken when the ship approximates periodic 

 resonance with the waves, we observe that the rolling is made up of individual 

 groups. The more regular the sea, and the more the apparent wave period equals 

 the period of the vessel, the greater the number of individual rolls constituting 

 a group, and, to a certain extent, the greater the amplitude of unrestricted rolling 

 reached. To ascertain the magnitude and character of the wave impulses a given 

 stabilizer would have to deal with in keeping the ship upright, one has to augment 

 the angles of roll recorded by the friction-damping angles for each single roll. 

 The latter angles are available from a natural dying-down record, taken at the 

 same steaming speed, and will be found surprisingly large where higher speeds 

 and effective bilge keels are present. It will also be observed that each group 

 represents two sets of wave impulses with some small impulses between them 

 where the ship is completely out of phase with the waves. The new non-resonance 

 type of stabilizer of Mr. Sperry is always in perfect tune with any impulse and 

 is found to enjoy twice as many "breathing spells" as would seem apparent from 

 the roll diagram, whereas a resonance device in the same sea will find between 

 the decreasing and increasing portions of the record a lapse in phase between the 

 sea and the ship, causing the pendulous mass either to give not enough or too much 

 counter moment, often actually producing roll. Its low specific quenching capacity 

 is, therefore, the very result of the resonance principle employed, and due to the 

 fact that only during an occasional roll increment it develops moments that are 

 in phase with and of the same magnitude as those received from the sea. 



Rear Admiral Bradley A. Fiske, Commander ist Division U. S. Atlantic 

 Fleet (Communicated) :— I have read the paper by Mr. Elmer A. Sperry, called 

 "Active Type of Stabihzing Gyro," with great interest and pleasure. What Mr. 

 Sperry has accomphshed already is most remarkable; and even if he does not 

 succeed in accomplishing everything that he is attempting, it seems sure that he 

 will accomplish enough to make him a benefactor of all "who go down to the sea 

 in ships." 



Whether Mr. Sperry will succeed in accomplishing all the great things that he 

 is attempting, I am, of course, unable to predict; but it is certain that it would 

 be extremely desirable that he should succeed, and therefore that he should be 

 given all possible encouragement. 



I have also glanced over the paper of Mr. Gillmor, called "The Sperry Gyro- 

 compass in Service." Mr. Sperry 's gyroscope compasses are fitted in the Florida, 

 and I am glad of the opportunity of testifying to their great efficiency for the pur- 



