St. Landry democrat., 1890-07-05
HOW FAR CAN WE SECT
simple Rules by which to Calculate tn
Range Of Vision.

simple Rules by which to Calculate the
Range Of Vision.
There is absolutely no limit to the
pormal vision, il the sight be unob-
structed- Yet we can see the stars,
which are trillions of miles away,
while we cannot see a tree twenty
miles distant. Why's It is true that
all objects diminish in apparent size
in direct proportion to distance, but
that is not the only reason. The chief
reason is that our vision is obstructed
by the curvature Of the earth. A
writer in Popular Science News gives
some figures to show how great this
curvature is.
It ia often matter OF interest and
importance to know how far we can
see from any given height, or, CON
versely, how far one must be above
the earth to see all object at a given
distance. The exact calculation Of
these figures would require the use OF
very complex formula, but for prac-
teal use, two very simple rules will
suffice.
Tho distance in miles at which an
object upon the surface Of the earth is
visible is equal to the square root Of
one and a half times the height of the
observer in feet above the surface. and
conversely.
The height in feet TO which All OBJ
server must be placed to see a distant
object is equal to two-thirds the
square of the distance in miles For
instance: Tho observer is in the rig
ging of n ship 100 feet above the
water, how far distant is the horizons
that ia. how far could all object
floating in the water be visible before
being hidden by the convexity OF the
earths One and one-half times 100 is
$50, and the square root Of $50 il, APP
proximately, ~, therefore the horizon
Is 12t miles distant
AS the deck of smaller vessels, like
pleasure yachts, IL rarely moro than
ten feet above the water, it follows
that the limit of vision from that point
is less than four miles in every direc-
ton.
An illustration OF the second rule
may be given as follows: a building is
So miles away; how high hill must
one climb in order to be able to see it3
As the square of the distance equals
1889, and two-thirds of that number
equals 726, it follows that we must
climb q hill 720 feet high before 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 observer.
must be taken Into consideration, but
this simply requires the duplication of
the problem. For instance: The
Washington monument is $50 feet
high; at what height must an observer
fifty miles away be in order to SEQ the
top of itl Surprising the observer to
stand upon the ground, we find by the
first rule that be could just see the
top % miles away, and 10 overcome
the remaining 81 miles, due to the
convexity of the earth, he would by
rule second have to climb to the height
of 294 feet.
Ii we apply similar calculations to
the Eiffel tower, the highest artificial
structure in the world, we obtain some
interesting results. Assuming the
height to be just LOCO feet, VS. find
that, standing ut the top, we enjoy
circle OF vision bounded BY horizon
80 miles distant, and that if another
similar tower should ever be erected,
it could be placed over 70 miles away
before the rays Of the electric lights
on their SUBMITS would be collapsed
by the intervening EARTH.
From the summit Of Mount Everest
in the Himalayas (27, GOO feet one
could see nearly 200 miles, provided
the air was clear enough, which
would rarely be the case.
Publishers Woes.
We have often heard Of the wall OF
the authors. Here is the wall Of the
publishers: a mors capracious, ty-
rannical and utterly spoiled set OF
people never existed than the book
buying public. The merest trifie gives
it offense. A price few cents too
high, cover of the wrong color, too
thick or too thin paper, too small or
too largo style Of type, publication
few days too late, two volumes instead
OF one or one instead Of two-any one
of these happenings is quite sufficient
TO kill book and leave its unfortu-
mats maker With nothing bat so many
pounds Of paper stock and old metal
10 turn into cash. Not one book in
twenty calls for third thousand, for
the book buying public" will otbuy
old books
Every season the makers are besieg-
ed by this vast array of unlaid spirits,
apparently doomed to walk the earth
and cry; Give lis new books with
out deigning even to intimate what
sort or Kind OF books it wants. It may
possibly--that is, there Is slight pos
sibihty that it may-take fancy to
some OF the few new ones; but, as for
the old 1T does not want them at any
price. The result is that these book
makers 60 on from year to year piling
up their store OF paper stock and old
metal. After all, why should these
booknakers expect to be freed from
the operation of fixed principles which
control other makers, such as coat
makers, hatmakers, shoemakers, etc.
What are booksa Simply manufac-
tured products, which il all civilized
nations have a certain vogue and then
pass tout OF fashion" American
Bookmaker.
Green House and Window Plants.
The plants are now all indoors, and,
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