i-10 



H. NAGAOKA. 



of a Thomson Graded Galvanometer. For obtaining strong mag- 

 netizing forces, a large coil wound in 12 layers was used with a 

 sufficient number of Bunsen cells. 



The arrangement of the coil and the twisting apparatus is 

 shewn in Fig. 5. 



Fig. J. 



il 



M 



Transient Current in Iron and Steel. 



The transient current produced by twisting an iron wire placed 

 in a magnetizing field has already been studied to a small extent. 

 The results of this earlier investigation have been given in the paper 

 referred to above. The method used in the experiments now to be 

 discussed was different from the earlier method ; and in addition, 

 wires of various thickness were examined. The present results are, 

 however, essentially the same, although there are many features which 

 passed unnoticed in the earlier and less detailed experiments. 



I shall first of all describe the experiment in the varying magnet- 

 izing held, the wire being, in each successive field, twisted to and 

 fro through a given constant angle. 



Most of the experiments were made on a soft iron wire, 1.24 

 mm. thick and 27 cm. long. The wire was carefully annealed, and 

 deprived of residual magnetism by heating it red hot as it lay in a 

 position perpendicular to the magnetic meridian. This precaution is 

 always necessary, for if there remain but a small quantity of residual 



