Year: 1865

When the density of two or more media are
alike, the rays of light pass through them
in straight or right lines. Hence. a GOOD
marksman, with his riff e, can take exact sight
and hit his mark. When one medium is more
dense than another, the rays are turned aside
and pass in curved lines. This, in Dioptrics,
Is called the Refraction of Light. Under such
circumstances, the eye sees its object, not
straight ahead, but in curved lire, cores
ponding to the circular passage of the light.


When the atmosphere is denser in one locali-
ty than 1t is in another, ball sent from
musket or cannon, in a right line, would
never hit the mark, however exact the sight
The more exact, indeed, the more certainly
would it Overreach or fall below.


Suppose you thrust straight stick-your
cane, for instance-half its length into clear
water, diagonally. 1t appears to be suddenly
bent at the surface of the water, and turned
up from the bottom. The part in the water ap-
pears considerably shorter than it was before
its immersion. In other words, an object un-
der water appears nearer the surface than
it really is. So, if you were to shoot or thrust
at fish, you must aim below him to hit your
object. A tub or other vessel filed with wa
ter, does not appear so deep as when empty.
The reason is, that water is denser medium
than air, and the rays of light are refracted,
whereby the bottom appears to be elevated, or
whereby the lower end of the stick or cane ap-
pears to be brought up, which gives crooked
appearance to the stick. --.-+


Take an empty bowl and place it in the win
dow-stooL Put quarter of dollar or any
silver bit in it. Now recede or stand back
from the window, until you are so far below
right line between your eye and the silverthat
the edge Of the bowl prevents your seeing it.
Whilst standing in this position, let a second
person approach the bowl with pitcher of
water and turn it in till the vessel is quite full
The bottom of the bowl appears to be elevat-
ed and exposes the silver to your sight so that
you can see it very clearly. But you do not
see it in a straight line; your sight, in fact, is
bent by the refiactel rays of light over the edge
of the bowl down to the bottom of it.


The principle on which these simple expert
ments can be made is that which Is to account
for the looming up of land or ships at sea,
which in fact are below the horizon, and
which cannot be seen on straight line. The
surface of the ocean, like that Of the land, Is
oval A vessel at the distance of few miles
is so far below you, that she is hid by the cir
Gle of the waters between you and her. But
at times, vessels mder such circumstances,
will suddenly appear to full view; and this Is
what, in nautical parlance, is called 'looming
up" The cause of this phenomenon is to te
found in the fact that the atmosphere, where
the distant vessel reposes upon the bosom of
the great deep, is of different density than it
is where you are; and the rays of light are re-
fracted or bent, so that you see crooked.


1t is on this principle that person win
sometimes see ooer hill to another elevation
ordinarily hid beyond it.


ID, l recollect curious incident related to us
BY the late Governor Isaac Hill of Concord,
N. IL, when on visit at the writer's residence
in Maine year OF two before he died. He
said that he went out one very cold morning
in January, and passing along State street,
what should he see but the Gun-Stock noun
tains, in northeast direction, which were
never seen before in Concord, being always
hid by Oak Hill, which lies between. The
mystery is solved on the plainest principle of
Dioptrics.e That was a very cold morning,
especially in the valley of the Merrimac,
where the city of Concord is situated 1t was
not SO cold at the Gun-Stock mountains
There was decided difference in The density
of the atmosphere In the two places. The
consequence was, that the rays of light were
refracted or bent Orer Oak Hill, so that Gov.
II. actually saw in circular line the Gun
Stock mountains below a straight line. To
revert to the experiment just named; Oak
Hill was the edge of the bowl, Gun-Stock
mountains the silver at the bottom of it,
which was apparently elevated by the refrac-
tion of light 80 as to be clearly seen from State
street in Concord. g. TRAx1.