INDUCTION OF MAGNETISM BY ELECTRICAL CURRENTS. 
291 
gathered that the magnetism induced by an equal current, increasing at first nearly 
with the section of the bars, becomes ultimately almost independent of their thick- 
ness, the attractions of the half-inch and inch burs being almost exactly equal to one 
another. 
Table II. 
Attraction, at 6 inches, of bars two yards long wrapped with 1 12 feet of wire. 
Diameter of bar. 
Intensity of 
current. 
Total change of 
magnetism by 
reversal of 
current. 
Magnetic set. 
Total change 
minus magnetic 
set. 
Set divided by 
square of current. 
Total change 
minus set, divided 
by current. 
r 
•0042 
•0150 
•0009 
•0141 
51-02 
3-357 
•0160 
•0826 
•0190 
•0636 
74-22 
3-975 
i X 
•0281 
•1440 
•0410 
•1030 
51-92 
3-665 
L 
■0988 
1-6531 
1-0030 
•6501 
102-75 
6-580 
r 
•0042 
•0451 
•0037 
•0414 
209-7o 
9-857 
•0167 
•2555 
•0513 
•2042 
183-94 
12-227 
\ inch < 
•0297 
•6227 
•2392 
•3835 
271-17 
12-912 
1 
•1048 
6-5007 
4-3887 
2*1120 
399-59 
20-152 
r 
•0044 
•0937 
•0095 
•0842 
490-70 
19-136 
•0192 
•5275 
•0870 
•4405 
236-00 
22-943 
inch < 
•0386 
1-2243 
•2597 
•9646 
174-30 
24-990 
L 
•1338 
10-6557 
4-9784 
5-6773 
278-08 
42-429 
r 
•0043 
•1280 
•0128 
•1152 
692-27 
26-791 
•0178 
•6088 
•0822 
•5266 
259-44 
29-584 
inch 
•0316 
1-0440 
•1833 
•8607 
183-56 
27-237 
L 
•1154 
6-1017 
1-6200 
4-4817 
121-65 
38-836 
1 
2 
3 
4 
5 
6 
7 
An inspection of the above results, obtained from bars of double length wrapped 
with twice the length of wire, leads to conclusions similar to those we drew from 
Table I. 
It appeared to me a matter of very great importance to investigate more closely 
the laws which regulate the magnetic set, and to determine with certainty whether 
the proportionality between the set and the square of the current, leading as it inevi- 
tably would to the better understanding of the nature of the molecular changes which 
occur in a magnetized bar, existed, and to what modifications it was subject. Seeing, 
therefore, that the supposed law began to fail when the thicker bars were employed, 
in which the mutual action of the particles distributed over a large section would 
naturally tend to counteract the magnetic induction developed on the exterior sur- 
face, I constructed two straight electro-magnets, one of an iron wire one yard long 
and 2^ of an inch in diameter, the other of an iron wire one yard long and 7^ of 
an inch in diameter. The former was wrapped with a single layer of covered copper 
wire i^th of an inch in diameter and 21 feet long, the latter similarly with wire 
27 feet long. The attractions of these wire electro-magnets were ascertained at 
