The Manitowoc pilot. [volume] (Manitowoc, Wis.) 1859-1932, 1899-06-22
ABOUT DAY AND MIGHT.
Duration of Twilight at Various De>
grees nf LatituSe on the
Surface OF the Globe.


twilight within the great tropical belt
encircling our planet is a widespread
one History, however, warns US that
beliefs need not necessarily accord with
facts. 1t might. indeed, almost be
said that they usually do not. The
toiling and moiling millions, the hum
bic units that, taken in the bulk, con-
stitute what is called great power
have neither the time nor the inclina-
ton to overhaul their opinions They
are not assailed by doubts as to wheth-
er the intellectual coffee which they
have at odd moments imbihed may not
have been mostly chicory. Such state
of mind unquestiouably makes more
happiness, and although such happiness
to that of. say, the cow, 1t is none the
less real for all of that.
Twilight is at its shortest at the
equator and increases with the latitude
at the equinoxes--at about the same
rate as that at.which the meridians de-
crease their distance from one another.
The increase is, therefore, slow in low
ATTITUDES and rapid near the poles,
Practical or civil twilight is the time
which elapses between the moment Of
the suns setting and the moment when
he is seven degrees of a great circle be-
low the horizon. AT the equator this
time cannot of course be less than %
minutes. At the edges of the tropio
zone ii is about 81 minutes. A person
with good eyesight will, should he care
to make the experiment, find that when
at sea and on or near the equator he is
able to read average type ON deck at
least rs minutes after the sun has set
without the aid of artificial light, and
when there is no moonlight. This is
She common sense seieXperiment by which
the duration Of practical twilight has
been determined. The actual dura-
ton is considerably longer than the
practical, and. even at the equator,
something like 10 minutes will elapse
before night holds undisputed sway,
This is the length Of the true, the astro-
nomical twilight
1t is at or near the equinoxes that
the phenome non under consideration is
at it's shortest all over the globe. AT
those periods II lasts at Honolulu 80
minutes; at San Francisco, 35; at Lon
don, As; at ST. Petersburg, 81; at the
arctic and antarctic circles, 72, and at
the poles, IS days. When, then, we
say that the poles have six months
light and six months darkness, it is
little more than facon de parler. The
north pole has no less than 222 days OF
practical daylight each year, the south
pole 215 days, and the equator 197 days.
Nansen, when in high northern lati-
tudes, was able TO read the Verdensgang
many days before the longed-for sun
rise followed the long winter night.
The great length of the twilight in
polar regions is a boon indeed to ex-
plorers. The popular imagination usu-
ally attaches itself to the great cold
they have to endure, but the real enemy
is the long darkness, which is tryingto
the enthusiasm of even a Nausen, a
Peary or jackson.
There is practically no difference in
the length of the twilight at the equa-
tor at the equinoxes and solstices. Even
at Honolulu it will not vary by more
than couple of minutes. But in the
higher latitudes the varying duration
is marked. In latitude 59h degrees,
for instance. it lasts Sc minutes at the
equinoxes, but at the summer solstice
it lasts from sunset to sunrise-that is
to say, from 8: 10 O'Clock till $50, or for
five hours and 40 minutes.
North or south of SO degrees prac-
tical twilight lasts all might at the
equinoXes. The sun is, 1T is true, only
IL hours above the horizon, but as he
cannot get more than seven degrees
below it, there is continual daylight for
"a hours. In such cities as Stockholm
and ST. Petersburg there are close Oh
TO Ia hours of daylight at those sea-
sons when day and night are said to
be equal. and at the equator itself the
day all the year round is made up of 13
hours daylight and II hours darkness.
1t must also be not forgotten that in
those ATTITUDES where the sun remains
for months below the horizon there is
during that period good deal of day
light, so that along the eighteenth par
allel north Ca little north of which the
JacksonHarmsworth expedition spent
three consecutive years in the Franz
Joseph islands), although the sun does
not rise between October 10 and Feb
ruary %. there is period of three
weeks following the final sunset and
another of the same length preceding
the first sunrise of the year, on each
day of which good type can be read
few minutes up to some hours without
artificial light.-San Francisco Chron-
icle.