Mr Benneit, The Rotation of the Non-Spinning Gyrostat 73 



of the conical movement seems to need more emphasis than it has 

 hitherto been awarded. It is here expKcitly isolated. 



The gyroscopic compass, Uke the magnetic compass, may at 

 times suffer disturbance from this same source, if the compass- 

 position in the ship and the run of the sea are such as to produce 

 a circular or elliptical movement of the binnacle. 



§ 6. It would be hard to trace to its primitive source the know- 

 ledge of the small piece of mechanics here discussed. It is really 

 implicit in all treatises on Rigid Dynamics, but fails to emerge 

 clearly amid the pressure of more important movements. Among 

 empiricists it must be well-nigh prehistoric. The sailor in coihng a 

 rope makes a winding motion of the feeding hand to remove the 

 kinks from the overtwist of the piece which is to form the next 

 turn of the coil. The circus clown, with the vertex of his conical 

 cap resting on his finger-tip, or the end of a stick, easily makes it 

 turn round and round; and the postman collecting his mail knows 

 how to twist up the neck of his bag with a circular movement of 

 the hand he holds it by. Later among empiricists are those who, 

 accustomed to handle magnetic compasses, are very familiar with 

 the rotation of the card produced so readily by giving the bowl 

 a horizontal circular translational movement (without rotation). 

 More lately still Mr S. G. Brown has noticed the conical motion 

 and its effect. In the abstract of his lecture to the British Associa- 

 tion* it is described as a "new phenomenon" and is stated as being 

 "explainable mathematically." More fully in his lecture to the 

 Royal Institutionf he states that in virtue of the "wobbling" 

 {videlicet conical) motion, "the needles and. card would then have 

 a force applied trying to carry the moving system round in the 

 direction of the wobble." This mode of expression is of course 

 entirely illegitimate. The rotational movement observed needs no 

 "force" to explain it; the very essence of the inertia effect is that 

 it occurs with no spin about the axis of rotation and no couple 

 about that line either. Mr Brown announces also (but without 

 demonstration) that if his compass-disc "is carried round in a 

 horizontal circular path without any wobble the plate still goes 

 round or tries to go round with the circular movement" and that 

 this "should be of interest to mathematicians." It seems likely that 

 the sheer paradox in angular momentum thus propounded will 

 readily dissolve when all the relevant physical data are revealed: 

 and meanwhile the interest is but that of a heresy resting on 

 hearsay. 



* British Association, Bournemouth, 1919. Evening Lecture, Fr. Sept. 12, 

 "The GjToscopic Compass." Abstract, 11. 9-14. 

 t Nature, March 11, 1920, p. 45, col. 2. 



