The Daily Ardmoreite. [volume] (Ardmore, Okla.) 1893-current, 1907-08-22
THE LIMIT OF VISION.
How Far Can tho wv . Eye See on
Land or o, ssSI

There is absolutely Il limit to the
normal vision II the sight le unob-
structcd. Yet we eau scc 'he stars,
which are tTilliOns of miles AWAY.
while We cannI see tree twenty
miles distant. WhyI i, Il true that
all objects diminish In apparent siz.'
in a direct proportion 10 distance, but
that is not the only reason. The CHIEF
reason Il that our vision IL obstruc,ed
by the curvature Of the earth A writ.
or In Popular Science News gives some
figures TO show how great this curva
ture IL.
II Is often n matter Of interest ana
importance to know how far We can
see from any given height or. con
versly. how far one must be above
the earth 10 49, an object AT given
distance. The exact calculation OF
there figures would requlr. the use ol
very complex formulate, bu, for pruc
teal use two very simple rules will
suffice.
Tie distance In miles at which an
object upon tho surface Of the earth
~ visible Is equal 10 the square root
Of one and one-haf times the height of
the observer In feet above the surface
and conversely.
The height in feet To which an oh
server must lie placed TO see n distinct
Of the distance in.miles. For instance.
IL the observer IL I'm the rigging OF n
ship loo feet above the water, how fur
distant il the horizon that Il, how far
could an object floating In the water
be visible before being hidden 10y the
convcxity OF the eArthf one and one
half times 100 Is 150, and the square
root Of iJ0 is approximately twelve and
onehalf; therefore the horizon IL
twelve and one half miles distant.
As the deck OF smaller vessels, like
pleasure yachts. Is rarely more than
ten feet above the water, II follows
that the limit ~ vision from that point
n less than four miles In every direc-
tion.
All Va Aii' S'''hh Va"
may be liyen a. follows: A building II
thirty-three miles away. How high n
hill must one climb In order to be able
TO see Il? As the square Of the dis
tance equals 1899 and two-thirds Of
that number equals 126. II follows that
we must climb II hill Ie8 feet high be
fore we are able to see the building,
even with the most powerful telescope.
Usually, however, the height Of the
object as we'll as that Of the obs@N
er must be taken into consideration,
hut this simply requires the dupllca.
ton Of the problem. For instance,
the Washington monument Is Boz feet
hiN. At what height must an oh
server Atty miles away be in order to
see the top Of ~ Sdpposing the oh.
server to stand upon the ground, We
find by the frs, rule that he could
just see the top twenty-nine miles
away, and TO overcome the remaining
twenty one miles. due 10 the cOnYeNlty
of the earth. he would by rule second
have to climb to the height Of 29i feet.
II We apply similar calculations 10
the Eirel tower, the highest artificial
structure In the world, We obtain some
interesting results. Assuming the
height to be just 100 feet. we find
that, standing at the top. We enjoy n
circle OF vision bounded by horizon
thI-y-nine miles distant and that II
another similar tower should ever be-
erected II could be placed over seven.
ty-eight miles away before the rays
Of the electric lights on their submits
would be ecllpsed by the Intervening
earth
From the summit OF Mount Everest
In the Hlmalayas $1,000 feet, onr
could see nearly POO miles, provided
the air was clear enough, which would
rarely be the case.