Warren sheaf. [volume] (Warren, Marshall County, Minn.) 1880-current, 1922-05-17
ASTRONOM
OBSERVATIONS
DIV Tor; ~ 1ohncn,
Tidal Force.
By Levi G. Johnson.

Tidal Force
Tidal force is the result of gravita-
ton as measured by the difference Of
its force on opposite sides of the
the Earth's center, depending on the
lance. The law that combines the
effects Of these two things, viz: Mass
and distance, is as follows: The tidal
force is proportional to the mass di-
rectly and to the cube Of the dis
tanceS. The moon, due to it's nearness
to us, is mainly responsible by it's
gravitational pull for the ocean tides.
AS we have already learned gravita-
ton decreases with the distance, there
fore the surface Of the Earth directly
under the moon is subject to stronger
pull than the center of the Earth
which therefore tends to draw the
surface up away from the center,
again the center is subject to stronger
pull than the opposite side, which like
wise tends to, pull the center away
from the opposite side, and if the
whole Earth was fluid it would sim
ply draw this fluid globe out into the
form of an ellipsoid, of which the
long diameter would be turned to-
wards the moon. But the Earth it.
self, being solid, cannot be drawn out
into this shape. while the ocean, be-
ing fluid, is thus drawn out. The. re-
suit is that we have high tides at the.
two ends of the ellipse into which the
ocean is drawn. and low tides in the
nlid-region. ~
The moons distance is about 80
times the Faiths radius, which means
that the distance from the moon to
the Earth's surface. center and OppO-
site surface. is to one another as the
numbers SO, 80 and 81. And as the
gravitation varies inversely with the
square Of the distance, therefore the
difference in pull on the Earth's sur
face and center is as 50 squared is to
60 squared, l. e., 34S1 to 5000, and
the difference in pull between the
Earth's center and opposite side is as
50 squared is to 81 squared, i. e., 5000
to 1921, which is nearly as much. Now
to calculate the tidal force Of the Sun,
it being about 800 times farther away
than the Moon (234OO times the
Earth's radius) the tidal force is dim
inished on account of distance to
1-59,319,OOO. While the Suns, mass
tweight) being 27OOO,OOO times that
OF the Moon, the Suns gain through
superior mass is therefore more than
overmatched by the effects Of greater
distance in the proportion of q to So.
The Moons tidal force upon the Earth
is therefore more than twice the
SUMS Now when the Sun and Moon
are in line, viz: new and full moon,
the two tides supplement each other,
(called spring tide), while when they
pull at right angles; viz, the Moons
quarters, they tend to neutralize each
other and rise only as high as the
superiority of the Moons force over
the Suns permit, (neap tide). But,
there is another circumstance that
varies the force, viz, the Moons
changing distance from the Earth, be-
ing at Perigee over $1,000 miles less
and at Apogee the same distance more,
than it's mean average, which results
in a variation of % per cent more at
Perigee and the same amount less at
Apogee than it's average. 1t is also
evident that the tidal force varies
with the Moons monthly swing North
and South, being greatest directly un-
der the Moon, and nearly none in
Polar regions. But, while the ocean
rides are the only manifest effects of
tidal force on the Earth, it seems
clear that the atmosphere must ex-
perience similar distortions. and even
the rigid body of the globe must suffer
an enormous strain, hence the suppo-
sition that tidal force has some influ-
ence over earthquakes. etc., but which
statistical observation has hitherto
failed to affirm. 1t reminds me Of pre-
dictions of disturbances on the Earth
caused by the positions of the planets :;
Of course the alleged influence could
be based on nothing but tidal force
Let us see then, how much force, they
can exert, H.: Jupiter's at opposition
is~1-16O,OO, of the moons average,
while Saturn's is 10 times less than
Jupiter's, etc. Then why believe in
such nonsense. -
Table for Week Of May 21-27.
I Sun Sun in Sun Moon