TaUp for Determining Moments of Inertia. 



649 



w 



attached by a small vice V. In the diagrams shown, fig. 1 

 represents a side view of the table, and fig. 2 a plan of the 

 top of the table. P is a pointer attached to the centre of the 

 table, and below is a fixed pointer P' resting 

 beneath. In the top of the table a circular pi 



Fig. 1. 



on a table 

 roove (fig. 2) is 



Kff. 2. 



w 



tr 



PI 



cut, in which small pieces of lead LLL can slide. These 

 pieces of lead form together half of a circular ring of 

 rectangular cross-section. In setting up the apparatus a 

 plumb-line is first hung from the supporting vice Y f and the 

 pointer P x placed immediately below. The plumb-line is 

 then removed and the table suspended by the wire W. The 

 body whose moment of inertia we require to determine is 

 placed at the given position on the table and the lead weights 

 LLL moved round in the groove until the centre of gravity 

 of the whole is in the axis V'P', this being ascertained by the 

 pointer P being exactly above P'. The table therefore 

 always oscillates about the same axis ; and since the lead 

 weights are at a fixed distance from this axis, the moment of 

 inertia of the table remains constant. Any alteration of tile 

 total moment of inertia is only that due to the body placed on 

 the table. • - 



