198 Prof. A. M. Mayer on the Magnetic Elongations 



retraction on making a circuit and an elongation on breaking it. 

 The fact that so eminent an investigator as Dr. Joule obtained, 

 on first passing a current round a bar of hard steel, results 

 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 annealed ; but 

 even this fact granted does not explain why all the steel rods I 

 experimented on gave retractions on passing the current a second 

 time after they had been " saturated >} during the first passage 

 of the current. 



Examining the results of my experiments on rod 00 (of hard 

 steel " drawn to blue "), we see that the phenomena are exactly 

 the reverse of those occurring in rods of iron in the same cir- 

 cumstances, except in this one particular, viz. that after break- 

 ing the first- made circuit the rod is permanently elongated; and 

 this result agrees with all of those obtained by Dr. Joule. 



The experiments on rod (of hard steel " drawn to yellow ") 

 are noteworthy. On making the first circuit this rod retracted 

 *4 of a division ; and on breaking this circuit the rod elongated, 

 but only *25 of a scale-division, thus leaving the rod permanently 

 retracted '15 of a division; so that this rod of hard steel, which 

 after the experiment remained a powerful magnet, is shorter than 

 it was before it had been magnetized. On passing the second 

 current round this rod, it, like the two preceding steel rods, 

 retracted *2 of a division ; and on breaking this circuit it elon- 

 gated by the same quantity ; so that after the second and sub- 

 sequent passages of the voltaic current it persisted in the retrac- 

 tion it received after the first-made circuit was broken. 



The experiments 1 have just given on rod differ in every 

 particular from any obtained by Dr. Joule on rods which were 

 not subjected to tractile strain. I cannot but regret that this 

 eminent physicist did not experiment on rods of very hard steel 

 freed as far as possible from all strains ; for then my experiments 

 would have been strictly comparable with his. The experiments 

 which Dr. Joule made on rods of hard steel (except those I have 

 already quoted) were conducted on rods subjected to tractions 

 going from 80 lbs. up to 1030 lbs., while my experiments were 

 made on rods so supported by brass springs that only a fraction 

 of their weights was supported by the Vs on which their ends 

 rested. 



Referring to Dr. Joule's experiments on a " soft steel wire 

 1 foot long, J of an inch in diameter, tension 80 lbs./' we find 

 that this rod behaved like one of soft iron free from strain with 

 currents deflecting his galvanometer from 34° 40' up to 56° 30' ; 

 but with currents below 34° 40' no action whatever was observed 

 to take place in the rod, except its magnetization ; but when the 



