St. Landry democrat., 1890-01-04
How Far Can We See r?

LITTLE BOYS AND GIRLS HAVE OFTEN
TRIED THIS.
| There is absolutely no limit to the nor
NAL vision, if the sight be unobstructed.
| Yet we can see the stars, which are trillions
of miles away, while we cannot see tree
twenty miles distant. Why? It is true
| that all objects diminish in apparent size
in q direct proportion to distance, but that
is not the only reason. The chief reason
is that our vision is INSTRUCTED by the
curvature of the earth. a writer in P0pu-
Tar Science NeoDs gives some figures to
show how great this curvature is.
1t is often a matter of interest and i'm
portance to know how far we can see from
any given height, or, conversely, how far
one must be ubovs the earth to see an OBJ
ject at given distance. The exact calcu-
lation of these figures would require the
use of very complex formulate. but for
practical use two very simple rules will
suffice.
The distance in miles at which an object
upon the surface of the earth IS visible is
equal to the square root of one and half
times the height of the observer in feet
above the surface, and conversely,
The height in feet to which an observer
might be placed to see distant object is
equal 10 two-thirds of the square of the
distance in miles. For instance The OBJ
server is in the rigging of ship 100 feet
above the water; how far distant is the
horizon that is, how far could an object
floating in the water be visible before bid
den by the convexity Of the earth? One
and one-half times 100 is $50, and the
square root of $50 u.s. approximately, 125,
therefore the horizon is 125 miles distant.
AS the deck of smaller vessels, like
pleasure yachts, is rarely more than ten
feet above the water, it follows that the
l!mit of vision from that point is less than
four miles in every direction.
An illustration of the second rule may
be given as follows: A building is thirty
three miles away; how high hill must
one climb in order TO be able to see it Z AS
the square of the distance equals 1883, and
two thirds of that number equals 726, it
follows that we must climb hill 726 feet
high before we are able TO see the build
ing, even with the most powerful telescope.
Usually, however, the height Of the OBJ
iect 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 552 feet high at what height must an
observer fifty miles away be in order to
see the top of it? supposlng this observer
to stand upon the ground, we find by the
first rule that he could just see the top
twenty nine miles away, and to overcome
the remaining twenty-one miles, due to
the convexity of the earth, he would, by
Rule 2, have to climb to the height of 294
feet.
If we apply similar calculations to the
Elffel tower, the highest artificial struc
ture in the world, we obtain some interest
ing results. Assuming the height to be
just 1000 feet, we Ind that standing at the
top we enjoy circle of vision bounded by
3 horizon thirty-nine miles distant, and
that if another similar tower should ever
be erected it could be placed over seventy
eight miles away before the rays of the
electric lights on their submits would be
9clipsed By the intervening earth.
From the summit of Mount Everest in
the Himalayas (27,00O, one could see
nearly 200 miles, provided this air was
clear enough, which would rarely be the
,age.-Go!den Days.
Have we g Christian civilization? We
ire told in the city of New York $50 600
children are day and night under the de-
influences of the saloon. We
ire told by the Citizens League of Chi
ago that 10000 children go DAY after day
INTO your saloons and drink and bring
4wsy drink. We have heard from the
platform here of your $40, 000, 900 for liquor
md see, 5000, 00l for beer. Do you think
he churches point heaveawsrd? Do you
hink great societies that meet together
md send away their millions to the heather