Richmond daily palladium. [volume] (Richmond, Ind.) 1876-1904, 1890-01-17
HOW FAR CAN WE seq
00Dls Rules by which to Cale1Iafs Dc
Range of Vision.

Range Of Vision.
There is absolutely no limit to the
normal vision, If 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 Whyi 1t 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 INSTRUCTED
by the curvature of the earth. A
writer in Popular Science News gives
some figures to show how great this
curvature is.
It is often a matter of interest and
importance to know how far we can
zee from any given height, or, con-
versely, how far one must be above
the earth to see an object at given
distance The exact calculation of
these figures would require the use Of
very complex formulR, but for prao-
teal use, two very simple rul viii
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 OBJ
server must be placed to see distant
object Is equal to two-thirds the
square of the distance in miles. For
instance: The observer is in the rig
ging of ship 100 feet above the
water, how far distant is the horizonf
that is. how far could an object
floating in the water be visible before
being hidden by the convexity of the
earth2 One and one-half times 100 Is
$50, and the square root of $50 is, ap-
Proximately, 12i, therefore the horizon
Is 12S miles distant
As the deck of smaller vessels. like
pleasure yachts, is rarely more than
ten feet above the water, 1t 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
81 miles away; how high a hill must |
one climb IN order to be able to see 1T |
As the square of the distance equals |
1853, and two-thirds of that number |
equals 726, it follows that we must |
climb a hill 72O feet high before W /
are able to see the building, even with
the most powerful telescope.
Usually, however, the height Of tho /
object Is we'll as that Of the oheesyse /
naust be taken into consideration, hnf
this amply requires the duplicAtio nof
he prDblena. For in1tanca. The
monument is tS2 fest
high i at what heightmust an ohoefver
fifty miles aWay b in order 70 ase flhe |
lop Of itiss GpEpoGng the observer to
Itand upon the ground, we find by the
drst rule that he could just see the
OPP 20 miles away, and to overcome
he remaining 81 miles, due to the
;onvexity of the earth, he would by
'ule second have to climb to the height
If 294 feet.
If we apply similar calculations to
he Eiffel tower, the highest artificial
tructure in the world, We obtain some
interesting results Assuming thet
leight to be just 1000 feet, we find
hat, standing at the ton. we enjoy a !
9 miles distant. and that if another
imilar tower should ever be erected,
could be placed over rs miles away
efore the rays of the electric lights !
n their SUBMITS would be eclipsed
y the intervening earth.
From the summit of Mount Everest
4 the Himalayas (27, 600 feet one ,
ould see nearly 200 miles, provided
ne air was clear enough, which !
Tould rarely be the case.