in changing the dimensions of Iron and Steel bars. 101 
elongation given to any of the soft iron rods when similarly 
experimented on. On passing the current around 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 re- 
tracting; again exhibiting a phenomenon the reverse of those 
observed in the rods of iron; and it is here important to re- 
mark, that all of the steel rods behaved in the same manner on 
the making and breaking 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, one yard long 
and a quarter of an inch in diameter, showed that the rod 
elongated on first passing the current; but on breaking this 
circuit, the rod retracted, while in my experiments, the ro 
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 experi- 
ment on this rod, pass around it a current sufficient to “ satu- 
rate” 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 increased, the retractions and elon- 
gations came nearer and nearer to equality, but in_no instance 
did he observe a retraction on passing a current and an elonga- 
hon on its cessation. F 
In his subsequent experiments, Dr. Joule worked on a steel 
tod of the same dimensions as that used in his former exper- 
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 jirst passing the current, and also in 
subsequently passing the current with successively increased 
intensities, a obtained results similar to those I observed in 
the rod of soft steel, but with this rod also he never observ 
a retraction on making a circuit, and an elongation on breaking 
It. The fact that so eminent an investigator as Dr. Joule 
i a a bar of soft steel, 
Tesults similar to those obtained by me with my bar of soft 
steel, leads me to suspect that the rod I experimented on may 
have retained some degree of “hardness” after it had been 
