648 Mr. W. H. Derriman on an Oscillating 



Equation (6) gives 



*V v _ 



7-v- 1 ' 



p "lir 

 V A, 



When the attenuation is rapid the attenuation-constant ap- 

 proaches the value -^ where A is the actual wave-lenath along 

 the wires. 



Queen's College, Belfast, 

 2nd March, 1903. 



LXVII. On an Oscillating Table for Determining Moments of 

 Inertia. By W. H. Derriman, B.Sc, Demonstrator in 

 Physics, University College, Liverpool*. 



TI1HE following description .of an oscillating table for 

 X determining moments of inertia is given in the hope 

 that the apparatus may prove useful in the laboratory, both 

 for determining moments of inertia of bodies experimentally, 

 and also for illustrating: some of the laws relating to moments 

 of inertia. 



With this apparatus the moment of inertia of a body can 

 be determined not only for axes which do, but also for axes 

 which do not pass through the centre of gravity of the 

 body. 



If a body of moment of inertia I is suspended by a wire and 

 allowed to make torsional vibrations, the time of vibration, t, 

 is given by the formula 



t = 2ir 



-A- 



where c is a constant depending on the dimensions and nature 

 of the material of the wire. This gives the well-known means 

 of determining the moment of inertia of a body about an axis 

 passing through the centre .of gravity of the body, the constant 

 c being determined by another experiment with a body of 

 known moment of inertia . 



The apparatus which it is the object of this paper to 

 describe consists of a circular wooden table TT supported 

 by brass rods liliR, to which the suspending wire W is 



* Communicated by the Physical Society : read January 23, 1903. 



