Evening star., 1938-09-20
OF STARS,
MEN AND ATOMS
Notebook of Science Progress
in Field, Laboratory
and Study.

in Field, Laboratory
and Study.
BY THOMAS r. HENRY.
There are sudden. irregular. unex-
planned changes in the rate of the earths
rotation on It's axis.
1t is as II the whirling planet were
given occasional pushes by some titanic
hand, with resulting increases In speed
OF as much as second in q year.
This discovery has just been an
nounced by DR.. Ernest w. Brown, pro-
fessor Of astronomy at Yale University,
in the annual report of the Smithsonian
Institution.
More than q century ago Simon New
comb. the celebrated American astron-
omer, found certain irregularities in the
motion OF the moon which he was un-
able to explain and which mathematic-
1ans ever since have failed to clear up
while they worked on the ASSUMPTION
that the moon itself was to blame. Grad.
ually they have calculated the lunar mo-
tions with ever greater and greater pre-
clsion, but still the puzzling, variations
persisted.
Dr. Brown has checked these moon OBJ
servations against observations Of the
movements of the sun compared with
those Of the earth for the past $50 years
and he finds almost precisely the same
differences. This leaves little room to
doubt, he says. that the real changes
observed are in the earths rate of rota-
ton. or the length Of the terrestrial dav.
His calculations show three such sud
den changes in the days length since
accurate solar observations are avail
able-one about 1890, another about
1897, and still another In 1917. The
1897 change altered the apparent length
OF the year by about q second.
Such changes, he says. are consider
able from an astronomical point Of
view, however little practical Importance
there may be to change Of q second in
the length OF the year. Just at present,
he says, the deviation Of the earth from
showing correct time Is greater than it
ever has been since observations were
made with sufficient accuracy and 1t is
reasonable to assume that a new change
may be expected soon.
Prof Brown advances what he stresses
Is only an hypothesis unsupported by OBJ
servation to account for the sudden
changes. The maximum variation thus
far observed would be accounted for by
an increase OF S inches in the earths
radius.
my own idea" he says, "is TO imagine
the existence Of layer Of material not
too far from the surface, which is at or
near critical temperature, the latter
being defined as one In which q small
change in temperature produces q rela-
lively large change in volume. There
are many substances which possess this
property. Thus a small change in the
interior condition of the earth might
easily produce relatively large change
IN the volume Of the layer, causing neces-
sary expansion or contraction at the
only portion which is free to move.
namely. that above the layer
"A change in volume OF considerably
less than l per cent in a layer with a
thickness Of mile would be amply suf-
flcient to take care OF the maximum OBJ
served change. Incidentally it may be
noted that the change in volume conse-
quent on any change in temperature
gives rapid method Of transfer of heat
in mass composed Of different ma
terials. for changes of pressure are
transferred without delay. and the COOL
ing OF hot mass could be made much
more rapid in this way than by mere
conduction.
The hypothesis gives a mechanism
for mountain building which has some
rather attractive features. The elasticity
Of the surface materials Of the earth is
amply sufficient to take care Of any
such increase in the volume Of its crust.
AS matter of fact, however, the sur
face is broken and assured in all direc-
tions, and the effect OF an expansion
would be to open these assures. They
would be partially filled by matter drop
ping from above or pressed in from be-
low. When the subsequent contraction
came, they would not be able to close.
and there would necessarily be q bulging
toward the surface.
The evidence We have indicates that
the major changes take place at inter-
walls Of the order Of century or less, so
that the same assures are likely to re-
peat their successive openings and clos
ings, resulting In successive elevations Of
the same region. The energy necessary
for the process is thus traced back to the
interior heat OF the earth, and the supply
would seem to be ample.
1T is not entirely impossible that the
hypothesis could be tested If and when
the next great change occurs. Some de-
vice which could measure very small
changes in the opening of fissure could
certainly be set up. If one costing a
small sum only could be constructed and
numbers of them placed in various parts
Of the earth. especially in those regions
where mountain building is known to be
going on, the information needed could
be obtained.