42 Scientific Proceedings, Royal Dublin Society. 



also to a slight degree at five times. So tliat if the wheel be tilted 

 and left to itself, as it gradually settles down, instead of the arcs 

 getting systematically less each time, the wheel is noticed to skip 

 one or two swings at five, several more at the "three period," and 

 likewise again on coming to accordance with the period of the 

 " spring rim," leaving a whole number of swings unperformed. 

 Experiments were made to see if the time of swing previous to 

 absorption or skipping of the swings was altered ; but no alteration 

 was detected : this, so far as the experiments go, not bearing out 

 the suggestion as to the cause of the discrepancy. 



After the " five period absorption," and again markedly so after 

 4 three period absorption," there is a recurrence of swings of about 

 the same length and slightly less than the absorbed ones. When 

 the wheel comes to any of these periods of accordance, the "spring 

 rim" is greatly disturbed and vibrates violently. In the case 

 where the periods are the same, the energy is never given back to 

 the wheel, which quickly stops ; but in the other two cases the rim 

 rapidly quiets down, giving back its energy to the wheel, which is 

 the cause of the persistence of the swings after each absorption. 



The analogy is very interesting between the absorption of 

 certain light vibrations by the molecules of some substances and 

 the absorption of certain vibrations by this apparatus. Also the 

 analogy with fluorescence perhaps would make the apparatus a 

 suitable mechanical model of fluorescence. The energy absorbed 

 at one period by the internal vibration is given out at another 

 period, as in fluorescence ; but it must be borne in mind that, unlike 

 the case of light, the energy is given out at a faster period than it 

 was absorbed at. 



