The morning news. [volume] (Savannah, Ga.) 1887-1900, 1895-05-26

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the seventeenth century that real inves-
tigation began.
IN fact II was nearly the end Of the
eighteenth century that some method was
imported into the investigation by the pub
ncation Of a series Of observations nv
FIoi- Busch. No theories. however. were
advanced sufficient to account for the phe-
nomena- The credit OF hrst Offering a
truly scientific explanation belongs to
Gaspard Monge 07i6-lSl0. an eminent
French mathematician who accompanied
Napoleon IN his expedition TO Egypt in
To understand the phenomenon OF mir
age Is not difficult, although the mathe-
NAUTICAL solutions OF every phase are I'M
/ doubtedly so. II is well known that the
density OF the atmosphere decreases with
the hight above the ground. This is the gen.
eral rule undoubtedly. II may. however.
happen that although the stratum OF air
nearest the ground Is usually the heaviest
It may become lighter than one above IT,.
as. for instance. when the air is intensely
heated by the suns rays. Such condition
Is what we may all accidental and Will be
due TO peculiarities OF the locality or to pc
culiar conditions of the atmosphere Now
We know that If ray of light passes from
more dense to a less dense medium. it
is refracted in a direction away from the
perpendicular to the surface at the point
where 1t enters the second medium. Sup
pose ray OF light to pass through a series
OF strata of decreasing density, and we
shall see that by the constant bending
away of the ray 1t will at last have di-
rection which is at right angles to the sur
face Of the medium.
What happens? 1t doets not enter the me-
dunn at all, but is totally reflected. You
can try this in a very simple way. Take
clear, round glass bottle, such as a flor
ence-oil flask, and half-ill 1t with water
Hold 1t above your head, and the surface
of the water is a mirror in which you sec
reflected the objects below the bottle. Or
take a large tumbler fill it with water.
place a spoon in it, hold it above you so
that you see the under-side of the surface
of the water and you will see the image of
the spoon.
Let us apply this to the ordinary mirage
as described by African travellers RAYS
from city, from palms, from rocks, from
mountains pass through the various strata
of air, of which the uppermost is densest,
until they strike the lowest, which is least
dense, let us say from the heat of the sand.
Here they are totally reflected and the
eye Of the traveller sees the objec.s reflect
ed as i'm mirror. The color of the sky is
also reflected and gives the appearance of
water, and so you have Rosetta" imaged
in an enchanted lake.
But it is evident that peculiarities Of
AONdlNy VERTICAL strata as
we'll as horizontal ones, of varying density
Here we get images distorted and magni-
fired by the simple effects of refraction for
We are looking at them, as 1t were,
through lenses, albeit they are of air, not
of crystal; such an effect may not unfre-
quently be observed by looking across a
river, a street or on the seashore. By this
we account for NJ. Bonnefont's famingoes
and thistledown ships.
In another phase of mirage, objects low
down near the horizon, or even below II,
appear lifted above II. Instances of this
are not uncommon. Helm has described
a case of this kind observed in the noun
tains of Thuringia, where he suddenly be-
held three lofty peaks appear above an
intermediate chain which generally con-
cealed them from sight, and these peaks
appeared to be so clearly defined that he
was able to distinguish, with an ordinary
glass, tufts of grass that were distant four
German miles (about Is of our miles," 1t
has even been said on credible authority
that at the Peak of Teneriffe mirage
made visible the Allegheny Mountains,
which are nearly 5000 miles awy.
The explanation is not far to seek. In
the former cases we considered the re-
suit of the density of the air decreasing
as Ii descends to the ground. In this case
the density increases, but not normally.
In a normal condition of the atmosphere,
a ray of light from the horizon is refract-
ed to such an extent that its path has
about twelfth part of the curvature of
the earth. But what IL conditions are
modified? If the density decreases with
the hight abnormally, il is possible that
the path of a ray may have q curvature
amounting to quarter and more OF the
curvature of a great circle of the earth
Strange as it may seem, it is possible in
this way to have "a gun which can shoot
round corner"
Proceeding to other phases of this mar
velous natural phenomenon, we come to
three cases which are connected with
each other: l. A reflection is seen above
the object, but it is inverted, and above
that a second reflection, which is erect. 2.
The inverted reflection is seen alone. 3.
The erect reflection is seen alone. Re-
markable instances of one or other of these
are on record In December, 1869, between
8 and o clock in the morning, the river
Seine, at Paris. appeared delineated in the
sky with its bridges, surrounding build
ings and the hundreds of gaslights upside
down.
Capt. Scoresby, the Arctic navigator,
narrates a curious incident. He says:
1--WE had already observed similar appari-
lions but this one was peculiar for the dis
tinctness of the reflection in spite of the
great distance of the vessel. Its contour
was so well defined that in looking at it
with Dollond's glass 1 could distinguish
the details of the mast and the hull OF
the ship, which l recognized as that Of
my father. On comparing our books we
saw that we were "a miles from each
each other that is, 1912 miles from the no
rizon, and far beyond the limits of vision"
Another instance is worthy of notice, be-
cause of the scientists who were witnesses
of il. Upon the shores of the Orinoco,
Humboldt and Bonpland discovered that
at noon the temperature of the %nd was
127 degrees, while at six yards above the
ground the temperature of the air was
only lO4 degrees. The hillocks of San Juan
and Ortez, the chain called the Gallera,
situated three or four leagues off, seemed
suspended in the air; the palm trees ap-
peared to have no hold on the ground,
and in the midst of the savannah of Cara
cas- these savants saw, at a distance of
mile and a half, herd of oxen appar-
emily in the air"
without entering upon a learned dis
ouisition, it will suffice to say that these
phases depend on what is called the re-
fractive index of each stratum of air,
which may be such as to cause intersec-
lions in the paths of the rays If there
is no intersection we only see the direct
image; if there are two intersections we
shall see the inverted image above the
h. L.,