78 K- HONDA. 



calculated the change of lateral dimension in these tubes. The 

 result for iron coincided qualitatively with that of Bidwell. 



The first experiment on the change of length of an iron 

 wire by the combined action of longitudinal and circular mag- 

 netizations Avas made by Beatson'^ who observed the diminution 

 of length at the moment when an electric current was passed 

 through a magnetized wire. A similar result was afterward 

 obtained by Righi.-^ The same experiment was also repeated by 

 Bidwell/' who observed a large increase in the change of length 

 by longitudinal magnetization of an iron wire carrying a current. 



2. Through the kindness of Prof. Nagaoka, his apparatus^^ 

 for the [measurement of the minute change of length was placed at 

 my disposal. The apparatus consists of a small optical lever with 

 an arrangement for temperature compensation on the same prin- 

 ciple as the gridiron pendulum. The rod, by which the change 

 of length is made sensible to the lever, was slightly modified. 



In the annexed figure, T is the tube to be tested, /^^and F' 



are two circular brass rings 

 nr LH P protrudins; from the tube 



R' Ji >■ at a distance of 1 cm. from 



Q> the ends, and soldered to a 



brass rod passing through 

 the axis of the tube. The magnetizing coil was wound round 

 the tube parallel to its length extending from F to F' to envelope 

 it completely, and so arranged that the tube could slide in the 

 coil with little friction. F in the lower part of the figure shows 



1) Beatson, Archives des. Sc. pliys. et nat. 2, 113, 1S46. 



2) Righi, Mem. di Bologna 4, 1, 1879; Beibl. 4, 802. 



3) Bidwell, Proc. Roy. Soc. .'il, 495, 1892 ; Beibl. 17, 582. 



4) Xagaoka, Phil. Mag. 2T, 131, 1894 ; Wied. Ann. r,s, 487, 1894. 



