186 AN EMPIRICAL STUDY OF GYRATING BODIES. 



my own deduction, and to proceed upon the assumption 

 that he intended to say that an instrument made as he 

 describes and suspended in that manner will not rotate 

 horizontally. 



It has been shown that a gyroscope (his four •' gyro- 

 stats ^ are really gyroscopes) will not stay up at all if not- 

 permitted to rotate horizontally. If, therefore, there is 

 no such rotation, the instrument will drop till the axes 

 are vertical, or as nearly so as the interference of the 

 wheels will permit. There will be no up and down vibra- 

 tion, 1 consequently there can be no continuing forever, 

 even in case of a frictionless machine, and there will be 

 no " drawing out of the rod to a distance proportional to 

 the weight." Lack of horizontal rotation puts an end 

 to the other propositions. 



But suppose that I have misunderstood the dis- 

 tinguished gentleman, and that the instrument being 

 "so arranged that there is no moment of momentum'' 1 

 means that it does revolve on a vertical axis. It is 

 necessary to take this view of the matter, because, in 

 fact, it does so revolve. 



It has been shown in every case of horizontal rotation 

 —friction or no friction — that the weight descends, not 

 to a "distance proportioned to the weight," but to the 

 lowest possible point that the form of the instrument 

 permits, and that this occurs whatever the weight, the 

 only difference being not in the distance it descends but 

 in its rate of downward movement. In no case — save 

 when the axes have become as nearly vertical as the form 

 of the instrument will permit — will the weight hang down 

 at rest ; and in no case, whatever, will " the hook be 

 drawn out to a distance proportional to the weigh t." 



There may, or there may not, be an up and down 



1 If a gyroscope be suspended from a point in the line of the axis in such a way as to give 

 freedom to vibrate in one plane like a pendulum, but with no liberty of lateral motion, it 

 will swing back and forth just the same in all respects, whether it is rotating or not. This, 

 however, is a very different kind of vibration from that of which Sir William speaks. 



170 



