Trouton — On Motion of a Body near Points of Equilibrium. 41 



nearly constant from 20 down to 4, and perhaps fairly so for the 

 rest, considering the difficulties of the experiments at very short 

 periods. 



A very interesting suggestion was made by Prof. Fitz Gerald as 

 to the cause of the observed time in the cases at the end of the table 

 being shorter than would be expected. It was to the effect, that 

 the acceleration of the wheel might be due to the period of oscilla- 

 tion being then comparable with the period of internal vibration of 

 the wheel about the axle as fixed, and to the tendency to isocronism 

 in vibrations, of approximately the same period as in the explana- 

 tions of Anomalous Dispersion. To test this, the rim of a smaller 

 wheel, its spokes being removed, was connected by spring spokes to 

 the axle, so as to present an artificial internal vibration not so 

 extremely fast as that of the wheel itself, thus giving opportunity 

 to observe the effect on the wheel at more manageable periods. 

 With this apparatus, the first thing noticed is that the wheel refuses 

 to vibrate through those arcs which have their time of swing nearly 

 the same as the time of the artificial internal vibration, and again 

 through those arcs which have a period about three times this, and 



E2 



