Evening star., 1939-12-09
Of Stors, Men
And Atoms
Notebook Of Science Progress
In Field, Laboratory
And Study

In Field, Laboratory
And Study
By Thomas r. Henry.
The direction of the earth's magnetic
field is constantly changing.
This Is so markedly true that If Co.
lumbus, who crossed the Atlantic by
means Of a compass indicating the direc-
ton Of NORTH" should repeat his mo-
mentous voyage with the same instru-
ments today he would land somewhere
on the North American coast instead Of
the West Indies.
The compass remains one Of the most
valuable of navigating instruments, but
constant observations must be made to
provide corrections for its deviation from
north. This is one Of the Jobs of the
Carnegie Institution of Washington. It
has made extensive determinations of
magnetic changes in recent times, both
at sea in the non-magnetic ships Galilee
and Carnegie and on land through nu-
merous expeditions to all parts of the
globe.
1t is especially concerned with data
which will help explain magnetism,
which still remains almost as much of
mystery as when the force was first dis
covered. Some Of the results of recent
investigations will be illustrated in a
model of the globe now being prepared
at the Department of Terrestrial Mag
netism here for the annual exhibition
of Carnegie scientific results which will
follow the annual meeting of the trustees
on December Is.
Without knowing the distribution of
magnetic attraction within the earth, it
is impossible to correlate the observed
changes reported by the explorers with
any other observable phenomenon.
Among the most recent fields of inves-
tigation followed by the Carnegie scien-
lists is the study of fossil magnetism"
the permanent alignment of magnetic
particles in clay and stone artifacts OF
known date. It is even possible to date
ancient flood deposits by the same meth
od-thus providing new clock of past
ages.
There are regions where the earth's
magnetism changes rapidly. Thus at
London the compass direction shifted by
IS degrees between 1860 and 1900, and
at Cape Town the strength of the earths
field has decreased about 20 per cent
since 1885. These gradual changes may
continue for century or more in one
direction at varying rates. and then may
be followed by changes in the reverse
direction. Measurements on the mag
netism of rocks indicate that similar
changes were in progress in prehistoric
times. The cause still is unknown. No.
body knows why the earth acts as a
magnet The cause lies deep in the
earth, beyond the present possibility of
exploration
Most of what is known about the
earth's interior is derived from study of
earthquake waves. Apparently the earth
consists of several major portions-a
rocky crust about 60 miles thick, man
tie Of material resembling glass, and a
central core, about half the diameter of
the whole globe, which has some of the
netism may originate in any one or all
three Of these regions. Sufficient mag
netic material to produce the earth's
magnetism does not exist in the crust,
Carnegie Institution measurements have
shown. At greater depths the tempera-
ture is probably too high for magnetic
material to exist. A magnet heated un-
til II }c hot 1ocoe &c ,,,,J
There is no way Of knowing the actual
temperature deep in the earth, nor can
science determine the effect of great
pressure in permitting material to remain
magnetic at higher temperatures The
best that can be done, the Carnegie
magnetism experts say, is to set up a
model reproducing the observed mag
netism and its secular change. The ma
jor portion Of the earth's magnetism OBJ
served near the surface could be pro-
duced by small but exceedingly strong
magnet placed near the center of the
globe. The axis of this magnet would
intersect the surface in polar regions,
but would not be quite parallel to the
earth's axis Of rotation. The rest of the
earth's magnetism could be represented
satisfactorily by about IL smaller mag
nets, each about one-flftieth as strong,
at suitable distances on the surface of
the core. The north poles Of some OF
| these magnets would be directed radially
outward and of some radially inward.
Once this model has been built the
secular changes can be accounted for by
adding still smaller magnets to the earth
each year. They must be fairly near the
surface. The magnets in the model,
representing the yearly secular change,
are about one-hundredth as strong as the
magnets in the residual field Thus if
secular change should continue as at
present for more than century, a new
residual field would develop resembling
In strength and complexity the present
| one.
The models are intended merely to give
picture of what is taking place. They
do not tell why it takes place, any more
| than photograph of tree tells why
| the tree grows. One can bore into tree
cut open its leaves and dig up it's roots,
| but the earth cannot be dissected to lay
bare the roots of magnetism. The ex-
planation promises to remain chal-
lenge to science for generations.
Proposes Drastic Action
BY United States.
Ernt~-