and Retractions of Rods of Iron and Steel, 197 



The phenomena of elongation and retraction observed in rods of 



steel. 



The phenomena observed on the magnetization and demag- 

 netization of the rods of steel have not been referred to. Here 

 we have presented to us remarkable results. On first passing 

 the current round rod 000, of soft steel, it elongated "8 of a 

 scale-division, behaving like a rod of soft iron ; but on breaking 

 the circuit, to my astonishment it again elongated '6 of a divi- 

 sion, thus leaving this rod with a permanent elongation of 1*4 

 o( a division ; and this elongation exceeds the permanent elon- 

 gation given to any of the soft-iron rods when similarly experi- 

 mented on. On passing the current round the rod for the 

 second time the soft-steel rod again did not act like a rod of iron ; 

 for it retracted *25 of a division, instead of elongating as did the 

 rods of iron in like circumstances; and on breaking this circuit 

 the rod elongated '25 of a division instead of retracting , again 

 exhibiting a phenomenon the reverse of those observed in the 

 rods of iron. And it is here important to remark that all the 

 steel rods behaved in the same manner on the making and break- 

 ing of the second and subsequently formed circuits. 



The results just described differ from those obtained by Dr. 

 Joule. Referring to his memoir (Phil. Mag. vol. xxx. p. 85), 

 we find that experiments on a rod of soft steel, 1 yard long and 

 i of an inch in diameter, showed that the rod elongated on first 

 passing the current ; but on breaking this circuit the rod re- 

 tracted, while in my experiments the rod again elongated on 

 breaking this circuit. Indeed the experiments of Dr. Joule in- 

 dicate that a rod of soft steel behaves like one of iron, except 

 that the elongations and retractions are of less extent than in the 

 case of an iron rod. It is important, however, to observe that 

 Dr. Joule did not, in his first experiment on this rod, pass 

 round it a current sufficient to "saturate" it, but gradually 

 increased the intensity of the current in successive experiments ; 

 and it is to be remarked that, as the intensity of the current in- 

 creased, the retractions and elongations came nearer and nearer 

 to equality ; but in no instance did he observe a retraction on 

 passing a current and an elongation on its cessation. 



In his subsequent experiments Dr. Joule worked on a steel 

 rod of the same dimensions as that used in his former experi- 

 ment ; but it was " hardened to a certain extent throughout its 

 whole length, but not to such a degree as entirely to resist the 

 action of the file." On first passing the current, and also on 

 subsequently passing the current with successively increased in- 

 tensities, he obtained results similar to those I observed in the 

 rod of soft steel ; but with this rod also he never observed a 



