388 



Mr. A. Mallock 



[May 2" 



Two methods of arriving at the desired information have been tried. 



The first is to record not only the periods, but also the ampli- 

 tudes of the free oscillations. In this method the oscillation is not 

 maintained, and the rate at which the motion dies out gives a 

 measure of the work lost at each instant. 



The second plan is to maintain a forced oscillation of constant 

 amplitude by the application of a known harmonic couple, and to 

 record the amplitude of the forced oscillation and the relation 

 between phases of this and of the maintaining couple. When these 

 elements are known it is a simple matter to calculate the work 

 expended in maintaining the constant amplitude. 



Cfc^ 



Fig. 5. 



In experiments such as these, where the object is to record 

 resistance, great care is required to exclude all sources of resistance 

 other than that which is to be measured, and in particular to elimi- 

 nate all chance of solid friction. Viscous resistance in the recording 

 mechanism when small can be determined by separate experiments 

 and its effects allowed for. 



The apparatus employed is on the lecture table, and as far as the 

 oscillating parts are concerned is the same as that used in the previous 

 series, except that provision is made for the application of a forcing 

 couple to the suspension wire, and a light horizontal arm is added 

 to the suspended rod, from the end of which arm a connecting rod 

 transmits the motion to the style recording the amplitudes on the 



