158 A. TANAK ABATE AND H. XAGAOKA. 



dicular to it had become slightly curved. This change of shape neces- 

 sarily altered the moment of inertia of the magnet. 



The dimension of the mau^net was therefore redetermined. Tlie 

 magnet was laid on a thick plane glass plate, and placed in contact 

 with the o-radaated side of the standard metre scale. This scale is of 

 brass, constructed by I'reithaupt (Hesse Casse]), and equal to one 

 metre, at 20" C. The two extreme edges of the magnet were slightly 

 convex, and were not distinct enouorh to serve as marks for measur- 

 inof the lenç^th of the mao-net. Two similar, ri^-ht-ano-led, o^lass 

 prisms were made to touch the fjices of the magnet, perpendicular 

 to its length. The edge of the prism was well defined, and was 

 brought in the same plane with that of the metre scale. The readings 

 of the edges of the prism were taken by means of a micrometer 

 microscope. The magnet was placed on the glass plate on all its four 

 faces successively, and the same series of observations repeated for each 

 position of the magnet. The magnet was then taken off and the 

 distance between the edges measured under the microscope. This 

 done, the mao-net was reversed and its lenoth measured no;ain in the 

 same way as before. 



To correct for change of lengtli l^y temperature, two thermometers 

 were placed beside the magnet, and two laid on the scnie. All these 

 thermometers were previously compared with the stand:ird thermo- 

 meter. Temperature readings were taken simultaneously with those 

 of the micrometer. Generally, the temperature of the mngnet did not 

 differ by more tlian 0".l from that of the scale. 



The following table gives the results of oljservations by ^lessrs. 

 Ota and iSTakamurii. 



