602 Prof. C. Barus on the 



gradually established*. "While the occurrence of beats id 

 a system of two degrees of freedom presents no novelty, 

 the evanescent character of the beating in the above 

 apparatus is to be pointed out. In order to make the two 

 component periods more nearly the same, ballast would 

 have to be removed from the watch. As I did not do this 

 I cannot say whether beating in such a case would be more 

 permanent. 



(5) The exceptional or intermediate periods are an average 

 between the two free compound periods, and are produced 

 when the system swings part of the time between successive 

 observations in one mode and part of the time in the other. 

 At first I was inclined to regard this transition from one 

 possible mode to the other as due to incident il influences (air- 

 currents, jar, temperature). It is probable, however, that 

 the case is to be sought in the mechanism itself, and due to a 

 change in the natural period of the balance-wheel according* 

 as the watch is more or less run down. Thus during an 

 interval of 36 hours, the watch at rest changed its rate from 1 

 + 5 sec. /hour during the first 12 hours, to —4 sec/hour 

 during the last 12 hours. Conformably with this I noted 

 that when the watch was allowed to run 36 hours without 

 rewinding, the violently swinging long periods first observed 

 were apt to fall off to the short periods of but slight motion 

 during the last twelve hours. Again, on starting the watch 

 for the long period immediately after winding, if the swing 

 is not quite wide enough, the short period eventually 

 supervenes. This observation is suggestive : the rata at 

 which energy is drained off by the resistances is in excess of 

 the rate at which energy is imparted to the rocking watch. 

 Like phases in the watch and the balance-wheel will not, in 

 general, be at once established, and hence the connecting 

 mechanism, as a rule, is ill adapted for effective transfer. 

 Unless the long period is approached from a longer period 

 (excessive swing of the pendulum), the former will thus be 

 out of reach and the vibration will fall off to the short 

 period. 



Furthermore, if the. period of the balance-wheel increases- 

 (as above) in the lapse of time, the corresponding long 

 period will also increase. Hence the watch is now put in 

 the same conditions observed when the watch is swung for 

 the long period from too short an arc. The short period is 

 eventually induced. 



(6) The above observations as a whole offer an interesting 



* An attempt to find the change of the period of these beats in the 

 lapse of time failed. 



