226 



Determination of the moment of inertness of the Ane- 

 mometer wings. 



The method employed was following: the wings with 

 their surroiinding ring were fixed on the centre of a mag- 

 net, fitted out with a mirror and a suspension-arrangement. 

 The time of oscillation of the magnet, whose moment of 

 inertness was well determined *), with out and with the wings, 

 was now observed and hence the moment calculated after 

 the formule 



M' 



Mo 



\-\-ta 



l-\-tfi)l\T.. 



ri \ 2 

 a \ 



M\ = M, 





T" \2 

 -L a 



t:. 



where 



i/o = moment of inertness of the magnet = 47.13 92 6 



+ 0.0 08 2 8. 



M' = moment of inertness of the vings I. 



M" = > ^ .II. 



t = the temperature. 



a and /? the linear dilatation- coefficients for the magnet 

 and the aluminium, T,,, T',,, T"n the times of oscillation of 

 the magnet without and with both wings. 



At the temperature of IT^^.o G we received 



Tn = 3\ 3 2 3 Tu = 1 Q". 2 8 8 T"„ r=: 9. 1 8 9 ; 



hence 



M\, = 1083.6 1 +0.18 J/"o = 312.66 and also M\ 

 more than 3 times of M"q 



^) It was one of the magnets used for earth-magnetic observa- 

 tions iu Sodankylä 1882 — 84. 



