Some of the first experiments I made, while professor at the Indiana
State University, were detailed in the March and August numbers,
1872, of the _Journal_ of the Franklin Institute, and I think showed
conclusively that the earth, by induction, renders all articles of iron,
steel, or tinned iron magnetic; possessing for the time being polarity,
after they have been in a settled position for a short time.
In Dr. I. C. Draper's "Year Book of Nature" for 1873, mention is made
of the experiments in which I found every rail of a N. and S. railroad
exhibiting polarity.
The same statements were repeated in one of a series of articles sent by
me to the _Indianapolis Daily Journal_, dated Jan. 20, 1877, in which I
used the following language:
"Every article of iron or steel or tinned iron, by the earth's
induction, becomes magnetic. Thus, if we examine our stoves, or a
doorlock, or long vertical hinge, or even a high tin cup, by holding a
delicate magnetic needle in the hand near those objects, we find the
earth has, by induction, attracted to the lower end of the stove
utensils, etc., the opposite magnetism from its own; and repelled to the
upper end of the stove, etc., the same magnetism which exists in our
northern hemisphere. Consequently, the bottom of the stove, or of the
hinge, cup, etc., will attract the south (or unmarked end) of our
needle; while the top of the stove, etc., attracts the north, or marked
end of our magnetic needle. If we apply our needle to the T rails of a
N. and S. railroad, we not only find that the lower flange of the rail
attracts the S. end of our needle, while the upper flange attracts the
N. end of our needle, but we also find, where the two rails come nearly
together (say within two inches), that the N. end of the rail attracts
the S. end of our needle, while the S. end of the rail attracts the N.
(or marked) end of our magnetic needle."
[Illustration: MAGNETISM ON RAILWAYS.]
Quite recently, being anxious to see the effect produced on the needle
by rails laid E. and W., I experimented on some recently laid here;
starting from a S. terminus, in the town of New Harmony, and gradually
curving northeast, until the road pursues a due east course to
Evansville. There is, however, a branch road of about half a mile, which
starts from the Wabash River, at a _west_ terminus, and runs due east
to join the other, near where that main track commences its northeast
curve. The results (more readily understood by an inspection of the
diagram) were as follows:
1. At the south terminus of the railroad, the rails on the east side of
the track as well as those on the west side attracted at their south
ends the marked end of a small magnetic needle, both at the upper and
lower flange; the usual vertical induction being in this case overcome
by the greater lateral induction. Whenever, on progressing north, the
rails were at least about two inches apart, the upper flange of the
north end of any rail would attract the unmarked, while the south end
of its neighbor or any other of the north and south laid rails would
attract the marked end.
2. The same results were obtained from rails laid all around the
northeast curve, and even after they had acquired a due west to east
course; showing that each rail acquired the same magnetic polarity which
would be exhibited by any magnetic needle oscillating freely in our
northern hemisphere, dipping also at its north end considerably downward
if suspended at its center of gravity.
3. Applying the needle at the _west_ terminus, a few anomalies were
observed; but, especially nearer the junction, the rails all gave the
normal result found on the main track.
4. The wheels of the cars standing on the north and south track followed
the same law, exhibiting both vertical and lateral induction, so that
the lower rims and the forward or north part of the periphery attracted
the unmarked end of the needle, while the upper and rear, or south
portions of the periphery of the wheel attracted the marked end.
5. The wheels of cars standing on the east and west road exhibited
the following modification. The lowest rim of all the wheels, whether
standing on the _north_ rails or on the _south_ rails of said track,
in consequence of vertical induction attracted the unmarked end of the
needle, and the upper rims attracted the marked end of the needle; but
the middle portions of the periphery, both anterior and posterior, of
the wheels standing on the north rail, attracted the unmarked end, while
similar middle portions of wheels standing on south rails attracted the
marked end; in consequence of horizontal induction, the wheels being
connected by iron axles, and thus presenting considerable extension
_across_ the track, viz., from south to north.
Magnetite seems to have acquired its polarity in the same manner,
namely by the earth's induction, when the ore contains a large enough
percentage of pure iron. A large specimen (6 in. long by 3½ deep and
weighing 5½ lb.) which I obtained from near Pilot Knob, Missouri,
exhibits polarity, not only at its lateral ends, but also vertically,
as the lower surface attracts the unmarked end of a needle, while the
plane, which evidently occupied the upper surface in its native bed,
attracts the marked end of the needle.
Iron fences invariably exhibit only the polarity by vertical induction;
so also small buckets, bells, etc. But in the case of a bell about 3 ft.
in diameter at its base, and over two feet deep, tapering to about a
foot in diameter at the top, I found that although the top attracted the
marked end of the needle, the bottom attracted the unmarked end of the
needle only around the northerly half of the circumference, while
the southern portion of this lower rim attracted the marked end in
consequence of lateral induction, as in N. and S. rails.
Thus, upon a comparison of all these facts, it would appear that, if
the magnetism induced by the earth is due to so-called currents of
electricity, those currents must be _underneath_ the rails, and must
move from west to east, under the south to north rails, and from south
to north under the west to east laid rails, as indicated by the arrows
in the diagram.
This accords perfectly with what we should theoretically expect, in our
northern hemisphere, if the electricity in the earth's crust is due to
thermo-electrical currents from east to west, namely, from the more
heated to the less heated portion, on any given latitude, while the
earth revolves from west to east; as well as also from electrical
currents trending from tropical to Arctic regions.
As the network of iron rails spreads from year to year more extensively
over our continent, it will be interesting to observe whether or not
any effect is produced, meteorological, agricultural, etc., by this
diffusion of magnetism.
It may further interest some of your readers to have attention called to
facts indicating