The Portland daily press. [volume] (Portland, Me.) 1862-1921, 1899-02-14
DAYLIGHT Ano DARKNESS.
twilight at Various Degrees Of Latitude
ON the surface OF the Globe.

fyrom tn. San Francisco ChroEicle)
The belle; that there Is little or no
twilight within the great tropical belt
encircling our planet is very widespread
one. History, however, warns us thW
beliefs need not necessarily accord Win
facts. 1t might, indeed, almost be said
that they usually 10 not. The tolhug
and moiling millions, the humble UNITS
that, taken In the bulk, constitute "h"'
Is called q "Ereai power" have nelther
tee time nor the inclination to overhaul
shtir opinions They are not assslleH Df
DOUBTS rs TO whether tho iuteileetuai
coffee which they have 1T odd moments
imbibed may not have been mostly enc
cory. Suchsa state of.,nind unqueS'lon"niy
makes more happiness, and although sNee
happiness may bear rather too mueh re-
semblance to that Of. say, the cow II Is
none the less real, for all that
Twilight is at its shortest at the equator
and increases with the latitude-at the
eouinoxes-at about the same rate as that
at which the meridians decrease their ais.
tance from one another. The increase Is
therefore. very slow in low ATTITUDES
and very rapid near the poles
Practical or civil twilight Is the time
which elapses between the moment oi
the suns setting and the moment when
he Is seven degrees of great circle beioW
the horizon AT the equator this time
cannot, of course, be less than IS minutes
At the edges of the tropic zone II Is about
81 minutes A person with good eye
sight will, should he care TO mako tine
experiment, nnd TINT when at sea ana
or near the equator he Is able TO reau
average type ON dsck for at least .
minutes after the sun has set without
the aid of artificial light, ana when
there is no moonlight. This is the com
nonsense experiment by which the uura-
tion of practical twilight bias been deter
mined. The actual duration Is consld-
erahly longer tbs the practical and even at
the equator, something like sevsnty min =
utes will elapse before nighS holds I'M
disputed sway 1hit is the length OF this
true, the astrC iomir a. twilight
IL is at or near the equinoyes that the
pnenomenon under consideration is at It's
shortest all over the globe. A those peri
ODDS it lasts at Honolulu 30 minutes; at
San Francisco, 35; at London, 40; at II
Petersburg, 81; at the Arctic and An
tarto circles, y, and at the poles, Is
DAYS When, then, we ray that the poles
have six months light and six months
darkness, it is little more than u facon
than 222 days of practical daylight zach
year, the South Pole, 2l5 days, and the
equator 1871 days. Nansen, when In nigh
northern attitudes, was able to read the
"Verdensgang many days before the
longed for sunrise following the long
winter night The great length of the
twilight In polar regions is boon In.
deed TO explorers. The popular imagina-
ton usually attaches itself to the great
otld they have to endure, but ths real
enemy is the long darkness, which Is try
ing to the enthusiasm OF evep:a NanseH'
u Peary or a jackson. g.
There is praoti ally no difference in the
lentth of the twilight at the equator at
the equinoxes ard solstinss. Even at Homo
lulu it will not vary by more than IA
couple of minutes. But In the higher
ATTITUDES the varying duration is very
marked. In latitude 80 H. degrees, for
instance, 1t lasts Of minutes at the ex-
quinoxes, but at { ee summer solstioe 1T
last from sunset to sunrise tnat is to
say, from 9. 10 o clock till 2. so, or for i've
hours aud forty minutes.
Noi tn or south of So degrees practical
twilight lasts all might" mt the
fuuint xes. 1hs sun is. 1t is true only
II hnurs above the horizon, but AS she can
AeJ more than seven de rees below
1t iers is continual day light for the "A
auHIs. In such cities as stockholm and
st. Petersburg there are close on TO IA
HuuTh vi dhi ilHib az th'oo s-te7Nho ~
day and night are said to be equal, and
at the equator itself the day all the year
round is made up of - hours daylight
and IL 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
a good deal of day light, so that along the
SOth parallel north (little north Of
which the Jack son Harmsworth expedi-
tion spent three consecutive years in the
Franz Joseph Islands although the sun
does not rise between October ~ and
February -, there is period of three
weeks following the final sunset and an
other OF the same length preceding the
first sunrise Of the year, on each day OF
which good type can be read for few
minutes up to some hours without arti
toial light.