in changing the dimensions of Iron and Steel bars. 97 
an uniform and known rate of rotation, the dot will on the elon- 
gation of the rod, describe a curved line which, referred to the 
appropriate ordinates, will give not only the time of the motion 
of elongation, but also the mode or law of this motion. Of 
course the motion of retraction can be studied in like manner. 
The following experiments were made on rod No.3, of English 
refined iron, and each result is the mean of 50 experiments. 
Time of elongation. Time of retraction. 
(1.) 25 cells, zisth of a second. ~oths of a second. 
(2.) one cell, 3ths “ s Ith ~ “ s 
It is thus seen that, with 25 cells, the duration of the retrac- 
tion is six times as long as the duration of the elongation, but 
with a current from one cell the phenomena are reversed and the 
duration of the elongation is three times that of the retraction. 
Determinations of the times occupied in the elongation and the re- 
action of a rod when the inner or the outer helix forms in tiself 
a closed conductor, while the current is passed, m the respective 
cases, in the outer and in the inner helix. 
(1.) Terminals of inner helix not joined. Ourrent passed 
through the outer helix from 25 cells. Elongation of the rod 
15 divisions. Times of elongation ;i,th of a second. Times 
heli ) Same results oe above when the terminals of the outer 
“sak were united, and the current passed through the inner 
5.) One cell used. When the terminals of the outer or inner 
helix were not united and the current passed respectively 
through the inner and outer helix, the elongation was 1:1 divis- 
tons. The time of elongation, ;°,ths of a second. The time of 
retraction ,2,ths of a second. 
(6.) One cell used. The terminals of inner helix united. . 
The elongation was 1‘1 divisions. Time of elongation, ;';ths of 
4second. Time of retraction 1,%,ths seconds. : 
(7.) Same result as experiment (6) when the terminals of 
Cuter helix were joined, and the current from one cell passe 
through the inner helix. 
To observe a rod slow! retracting during 13 of a second 
oat most remarkable sight, and suggests many thoughts as to 
teraction of the induced currents passing in the helices and 
Am. Jour. oe Vor. VI, No. 32.—Avevst, 1873. 
