The Washington times., 1922-07-13
FINDINGTHE MERIDIAN
IT'S AN EASY AND USEFUL THING TO DO !.
Simple Methods by Which Even Laymen
May Find Out About Where
True North Is.

proaches and the shadow swings
eastward on the board, II will be-
come shorter. II you have prop
erly proportioned the size Of the
circle to the height of the gnomon,
the end of the shadow will, at
some time. just touch the circle.
Mark that spot carefully. At
noon the shadow will be shortest,
and you may also mark the spot
where It's end falls at that mo-
ment. After noon the shadow will
lengthen, and when II again reach.
es the same circle with which you
began. mark the spot where the
point OF the shadow now touches
the circle. Then draw a straight
line Chord connecting the two
points where the end of the
shadow touched the circle, bisec:
that chord by line to the center,
and this will indicate the meridian.
II your work has been accurate
the point where you marked the
eno or the shadow at apparent
noon will lie on the line.
Still more accurate results may
De obtained by observations on
stars star which transits the
meridian south Of the zenith, like
the sun. may be chosen. and two
observations be made of II. when
II has equal attitudes. one east and
Ine other west Of the meridian.
This is in effect the shadow ana
Clrcle method in another form. Or
the observations may be made on
the pole star. which revolves
around the true pole in a very
small circle once every twenty-four
hours.
When the pole star is either
urctly above or directly below
,he true pole. II must necessarily
lie on the meridian, and at such n
time the line OF sight from your
eye TO the pole star Is in the yer.
tical plane OF the meridian. In
other words. you look trne north
when at such times you look At
that star.
The pole star crosses the merid-
ian twice every twenty-four hours.
once above and once below the
poie' the former being called It's
upper elimination and the latter
Tits lower elimination.
This IL OF great historic In,ere.t
because the pyramids OF ERypt,
and in particular the great Pyra.
mid. called the Pyramid OF Cheops.
were oriented and built by the aid
OF the culminations of the pole star
OF that day, which was quite A ar
ferent star from our Polaris.
You can tell with sufficient ar.
curacy for ordinary purposes when
the pole star Is on the meridian.
either above or below, by watch
two considerations Ursa Major Cthe
Great Dipperl and Cassiopeia tthe
Chalr). AT this time Of the year
the pole star Is practically true
north about 7;30 p. m, local time,
the star being then sat lower cui-
mlnation. When either the Great
Dipper or Cassiopeia is over the
pole the star Is on. or close to.
the meridian.
BY methods exactly similar, but
with instruments of superior ac-
curacy, the meridian Of every
place where an astronomical OBJ
serVatory exists Is determined.
For temporary purposes. like
those OF a surveyor or explorer.
portable instruments are employ
ed. The line Of the meridian being
once ascertained, monumental
marks may serve to indicate II
for future use.
The great weakness Of magnetic
reference lines comes from their
variability. By variation Of the
needle" you no doubt mean what
Is more correctly described a.
"declination," which means the
departure of the needle from the
true magnetic meridian, which Il.
self is by no means Identical with
the terrestrial and celestial meri.
dian that we use as a north-a
south line. Not only does the
pointing OF the needle differ at diff.
ferent places. but II varies period
ically in the same place. The ul-
innate cause of these variations
remains to be discovered.