Evening star., 1922-03-19
Magnetism of Railways.

THAT the rails on a railroad be-
come magnets under the inhu-
ence of the earth's magnetic field has
long been known. Any steel bar held
In the direction OF magnetic north ana
south and hammered so as to jolt its
molecules will assume a magnetic
state. In the case of the railroad
passing trains furnish the necessary
hammering. Experiments on the
magnetism OF rails have been made
ana have brought to light some facts
of interest.
Under the influence of the earth's
magnetic field steel rails subjected to-
mechanical actions assume perma-'
nent magnetization. The case IL the
same AZ with a steel wire or bar,
which, being in a magnetic field, nat
ural or artificial, becomes magnetized
whenever through torsion or trac-
tion the elastic limit of the metal is
exceeded.
With reference to the rails he ex-
amined, one engineer offers the fol-
lowing observations: Two magneti-
cations are simultaneously developed
in perpendicular directions one
along the length of the rail, the other ,
in the direction of its height-and
these two forces are superposed, one
being stronger than the other, ac-
cording to circumstances.
In fact, a rail in position is affect.
ed at once by the horizontal compo-
nent and by the vertical component Of
the earth's magnetic field; the former
tends to develop a longitudinal mag
| netixation, the latter a vertical mag
netization, as may be shown by the
compass.
The longitudinal magnetism 10
more decided II the rail is in the dh.
rection Of the magnetic meridian. =
becomes insefisible with rails Wf0eo
axis makes an angle OF moro thais
thirty degrees with the meridian.
The magnetization is ordinarily
stronger when the rail has been
greatly used: that is to say. when 1t
has been laid a long time and sub
jected to mechanical strain that has
contributed to modify the molecular
structure Of the metal.
The preceding statements apply to
rails that have been taken up. When
in place the line of rails with their
connections of magnetic metal form.
30 to speak. a single magnetic bar;
the magnetism IL latent and does not
appear until the rails are freed by
removing the plates. The case Is the
same as with long bar magnet; the
neutral zone, intermediate between
tho poles, gives TO appearance OF
maxnetism and, nevertheless, when
the bar is broken into several pieces
all are found to be magnetized.
It Is only in badly kept roads. where
Joints are too loose or badly Joined. or
where contiguous rails are on sensi-
bly, different levels, that we can de-
tect magnetixation. 1t Is also evident
1t switches, crossings, etc.. and at
all points where there is Q Jolt when
. train passes.
When the line Is east and west .
curious thing occurs. When q com
pash is held over a joint the north
pole turns either toward east or west,
but always in the direction in which
, the trains move when the track -
double. This il because the track be-
| Ing at right angles to the magnetic
meridian, the horizontal magnettsa-
ton is absent and there is nothing to
interfere wit the vertical compo-
nent. Now. ut each joint the end OF
the rail on which the wheel Is enter
ink IL always more powerfully ham
merkd than that which 1t is eaving.
ana on It IL developed more strongly
the south pole induced by this vefti-
cal component OF the earth's mag
| netism. =