Scientific Proceedings, Royal Dublin Society. 



StFMMARY. 



In parts I and II of this paper,' wliere the results of experiments on soft 

 iron wires only are given, the main conclusions arrived at were : — (1) The 

 amount of transient current produced by twisting a soft iron wire placed in 

 a longitudinal magnetic field, is inversely proportional to the load on the 

 end of the wire, for a range from about 10* to 3 x 10= grammes per square 

 cm., and when the load was increased about three times the transient current 

 was about haloed. (2) With a given longitudinal magnetic field round the 

 wire, and a given longitudinal stress per sq. cm. on it, the transient current 

 produced by twisting the wire was fovmd to be directly proportional to its 

 cross-sectional area. (3) With a given longitudinal magnetic field round 

 the wire, and a given current density in it, the twist of the free end of the 

 wire was found to be inversely proportional to the load ; and when the load 

 was increased seven times, the twist was decreased about 14 per cent. 

 (4) The current density in the wires being the same, the maximum twist of 

 the free end was found to be directly proportional to the cross-sectional area 

 of the wire, and when the cross-sectional area of the wire was increased 

 4'7 times, the maximum twist was increased about three times. 



For the experiments which form the subject of the present Part III of 

 the paper, a new batch of the best Swedish charcoal iron was obtained, 

 which is of practically the same quality as was used in the previous 

 experiments. 



With the soft iron wire of hardness H^ when placed in a longitudinal 

 magnetic field of 2"5 units, the twist of the free end is inversely proportional 

 to the load on the wire, and when the load is increased six times, the twist is 

 decreased 27 per cent. This diminution is about 7 per cent, more than was 

 found with a previous soft iron wire tested under the same conditions, but 

 this can be easily accounted for by the fact that the latter wire was a little 

 softer and a little larger than the former one. 



In all the three states of hardness Ho, Hi, and H2, the twist of the free 

 end is proportional to the length of the wire, and when the length of the 

 wire is halved, both the area of the cyclic curve in a field of 2*5 units and 

 the twist are decreased 50 per cent. ; also in the three cases the twist is 

 inversely proportional to the load on the end of the wire, and the harder the 

 wire, the more the twist is diminished as the load is increased. When the 

 load is increased six times, the twist is decreased 27 per cent, in the wire of 



1 Scient. Proc. Koy. Dublin Soc, 1909, vol. xii., pp. 101 and 175. 



