New-York tribune., 1919-12-22

travei around the sun in perfectly cir
cular orbits ard that a correct diagram
OF all these orbits could be drawn on q
piece of paper, where they would ap-
pear as circles all having the same
center, where the sun ia situated. Such
diagram would not be perfectly cor
rect, but it would be a close approx
nation 10 the actual facts. Anything
that would be true if the planets
moved ,as indicated in this diagram
would be equally true in a diagram
representing the actual motions with
perfect exactness. The difference would
be merely a matter Of mathematical
detail, not affecting the general prob
lem.
To Appear Near Neptune
"Considering our planets as moving
IN their circular orbits, we can glance
at them at some particular moment Of
time, say, January 81, 1920. On that
date we should see each planet in a
particular point Of its orbit, and astro-
nomical calculations show that on that
date the earth and planet Neptune are
so placed that Neptune will be visible
to US practically all night and will. rise
very high in the sky at midnight. This
being understood, let us consider how
the force of gravitation controls or
bltal motions of the planets. This con-
trolling force comes almost entirely
from the sun, but in a slight degree
each planet so eXerts a gravltatlOnal
pull on each Of the others. We can
imagine that there exists this sup
posed unknown new planet, whose orbit
is far outside that Of Neptune
I'VE may also suppose that the new
planet is so placed in its orbit that it,
too, will be high up in the sky at mid
night, like Neptune. In that case we
should see Neptune and the new planet
so that they would appear quite close
together. The new planet will, of
course, be further away than Neptune,
and if conditions were right it mi light
be directly behind Neptune, so as to be
eclipsed from our view. In that case
the gravitational pull Of the new planet
exerted upon Neptune would tend to
pull Neptune away from US. This
could not be observed because moving
Neptune away little would not change
the direction in which we see it, In
the same way man walking directly
away from an observer does not change
his appearance when he takes a step
or two but if he s not walking ex-
actly away from the observer single
step may change his position per
ceptibly with respect to surrounding
houses and trees.
"ln the case of Neptune and the new
planet the two bodies will presumably
not be exactly in the same direction as
seen from the earth; therefore the new
planet will not merely pull Neptune
away from US, but will pull it to some
extent in a sidewise direction. And
there are excellent surrounding OBJ
jects by means of which we could de-
tect 2 sidewise motion of Neptune be-
cause we have in outer space a back
ground of stars with which to compare
Neptunc's position. Such comparisons
have been made ever since the discov-
cry Of Neptune, and in late years Nep-
-une has shown indications Of being
subjected to just such a sidewise pull
rs we are imagining.
Sometimes Neptune is pulled to one
side and sometimes to the other, or, in
other words, its orbita motion is some
tines retarded little and sometimes
accelerated This is just what we
should expect because the supposed
outer planet would alternately bring
about just these two results"