290 
MR. JOULE’S INTRODUCTORY RESEARCH ON THE 
Table I, 
Attraction, at 6 inches, of bars one yard long wrapped with 56 feet of wire. 
Diameter of bar. 
Intensity of 
current. 
Total change of 
magnetism by 
reversal of 
Magnetic set. 
Total change 
minus magnetic 
set. 
Set divided by 
square of current. 
Total change 
minus set, divided 
by current. 
current. 
r 
•0044 
•0164 
•0014 
•0150 
72-31 
3-409 
i i'wli < 
•0197 
•1012 
•0266 
•0746 
68-54 
3-787 
•0417 
•3020 
•1085 
•1935 
62-40 
4-640 
L 
•1450 
2-7747 
1-7036 
1-0711 
81-03 
7-387 
r 
•0041 
•0364 
•0038 
•0326 
226-05 
7-951 
i inch < 
•0197 
•0414 
•2336 
•8798 
•0628 
•4085 
•1708 
•4713 
161-82 
238-34 
8-670 
11-384 
L 
•1446 
8-2871 
4-9179 
3-3692 
235-20 
23-300 
r 
•0045 
•0857 
•0113 
•0744 
558-02 
16-533 
^ inch 
•0194 
•4573 
•0882 
•3691 
234-35 
19-026 
•0419 
1-2162 
•3207 
•8955 
182-67 
21-372 
•1460 
8-6948 
2*7628 
5-9320 
129-61 
40-630 
r 
•0045 
•1017 
•0128 
•0889 
632-10 
19-755 
inch <; 
•0195 
•5089 
•0817 
•4272 
214-86 
21-908 
•0416 
1-0935 
•1377 
•9558 
79-57 
22-976 
•1404 
5-6858 
1-0248 
4-6610 
51-99 
33-198 
1 
2 
3 
4 
5 
6 
7 
Although the covered wire was fine and wound close to the iron, it could not be 
expected to act with exactly equal advantage in the bars of small as of large diameter, 
chiefly on account of the circuit taken by the wire being, relatively to the circum- 
ference of the bar, greater in the small than in the large bars. In comparing the 
results together, it should therefore be borne in mind, that those obtained with the 
bar of ^th of an inch diameter are somewhat diminished from the above circum- 
stance. 
A very cursory inspection of the results convinced me that the magnetic set 
followed a very different law from that which regulated the magnetic action under 
the influence of the current. I have therefore subtracted the former from the latter 
in the 5th column of the Table. Even after this separation has been effected, it will 
be seen from column 7 that the magnetic action over and above the set increases 
with considerably greater rapidity than the intensity of the current, a result which 
is I believe owing to a portion of the set actually existing during the action of the 
current being destroyed on the breaking of the circuit. It will be remarked, on 
inspecting column 6, that the set of the bars of ^ and of an inch diameter increases 
nearly in proportion to the square of the current, but that with the thicker bars the 
ratio is diminished ; so that, although the set of the bars of small diameter is greater 
than that of the large bars when a current of powerful intensity is employed, the 
reverse takes place when a weak stream is used. From the 7th column it may be 
