Moment of Inertia of Magnets. 131 



§ 1. Determination of the Moment of Inertia of a 

 Standard Bar. 



The instrument is shown in fig. 1. It consists of a cradle, 

 A, suspended by a stout quartz fibre (length 30 cms., 

 diameter 0*37 mm.). The bar, B, to be tested rests on this 



Fie. 1. 



cradle while the position o£ the cradle is read by reflexion o£ 

 a scale in the mirror C. A table, I, which can be raised or 

 lowered by a lever, K, has a hole-slot-and-plane on its upper 

 surface, and the three feet, F, Gr, H, of the cradle rest in these 

 when the table is raised. The conical hole, 0, in which the 

 leg F rests is so placed that the cradle when supported on the 

 table lies about half a millimetre to the left of its position 



when hanging free. The 



object 

 K2 



of this arrangement is that 



