The semi-weekly messenger. [volume] (Wilmington, N.C.) 1897-1908, 1899-09-01

Variance In Time at Different Points
on the Globe explained

we shall now consider the question of
time differences between different
places on the earth. This is a matter |
which man persons find most per- |
picking, and yet it is essentially quite
simple in principle. Travellers are, Of
course, we'll acquainted with the fact
that their watches often need to be
reset when they arrive at their desti-
nation. Yet few ever stop to ask the
cause. Let us consider for a moment |
our methods of measuring time. We
go by the sun. If we leave out of ac-
count some small irregularities of the
suns motion that are Of no conse-
quence for our present purpose we may
lay down this fundamental principle:
When the sun reaches it's highest posi-
ton in the sky it is II o'clock, or noon.
For the sun, as we know, rises each
morning in the east, slowly goes up
higher n higher in the sky, and at
last begins to descend again toward
the west. But it is clear that as the sun
travels from east to west it must pass
over the eastern one Of any two cities
sooner than the western one. When it
reaches it's greatest height over a
western city it has therefore already
passed its greatest height over an east
ern One. In other words, when it is
moor, or II o'clock, in the western city
it is already afternoon in the eastern
city. This is the simple and evident
cause of time differences in different
parts of the country. OF any two places
the eastern one always has later time
than the western. When VIC consider
the matter in this way there is not the
slightest difficulty in understanding
how time differences arise. They will,
Of course, be greatest for places that
are very far apart in an east or west
direction. And this brings US again to
the subject of longitude, which, as we
I'VE already said, plays an important
part in all questions relating to time.
For longitude is used to measure the
distance in an east and west direction
between different parts of the earth.
If we consider the earth as a large ball
we can imagine a series of great circles
drawn on it's surface and passing di-
rectly from the south pole to the north
pole. Such a circle could be drawn
through any point on the earth. If we
imagine a pair of them drawn through
two cities, such as New York and Lon
don, the longitude difference of these
two cities is defined as the angle at
the pole between the two great circles
in question. The size of this angle can
be expressed in degrees. If we then
wish to know the difference in time
between New York and London in
hours we need only divide their longi-
tude difference in degrees by the num-
Der Is. In just this way we can get
the time difference Of any two places.
We can measure the longitude differ
ence on a map, and then divide by Is
to get the time difference.
These time differences can some
times become quite large. indeed, for
two places differing $50 degrees in lon
gitude, the time difference will evident
ly be no less than twelve hOursa Most
of the civilized nations have agreed in
formally to adopt some one city as the
undamen point from which all lon
gitudes are to be counted. Up to the
present we have considered only lon
gitude differences. When we speak of
the longitude of any city we mean it's
longitude difference from the place
chosen by common consent as the orr
gin for measuring lOngltudes. The
town almost universally used for this
purpose is Greenwich, near London, in
England. Here is situated the British
royal observatory, one of the oldest and
most important institutions Of it's kind
in the world. The great longitude cir
Gle passing through the center Of the
astronomical transit at the Greenwich
observatory is the fundamental longi-
tude circle of the earth. The longitude
of any other town is then simply the
angle at the pole between the longitude
circle through that town and the fun
damental Greenwich one here de-
scribed.
Longitudes are counted both east
ward and westward from Greenwich.
Thus New York is in "a degrees west
longitude, while Berlin is in IA degrees
east longitude. This has led to a rath-
er curious state of affairs in those
parts Of the earth whose longitude is
nearly $50 degrees east or west. There
- - I - IN tho yo-+
of the world, and if we imagine for a
momen one whose longitude is Just $50
degrees we shall have the following re-
result as to it's time differ
enc from Greenwich: We have seen
that of any two places the eastern al
ways has the later time. Now, since
our imaginary island is exactly $50 de-
grees from Greenwich, we can consid-
er it as being either $50 degrees east or
$50 degrees west. But if we call it $50
degrees east, it's time will we twelve
hours later thar Greenwich, and if we
call it $50 degrees west, it's time will
be twelve hours earlier than Green
wich. Evidently there will be a differ
ence of just twenty-four hours, or one
whole day, between these two possible
ways of reckoning its time. This cir
cumstance has actually led to consider
! able confusion in some of the islands
, of the Pacific acean. The ~naVigators
who discovered the various islands nat
urally gave them the date which they
brought from Europe. And as some of
these ~navigators sailed eastward.
around he Cape of Good Hope, and
others westward around Cape Horn,
the dates they gave TO the several is
lands differed by just one day.
The state of affairs at the present
time has been adjusted by a sort of
informal agreement. An arbitrary line
has been. drawn on the map of the
world near the $50 degrees longitude
circle. and it has been decided that the
islands on the east side of this line
shall count their longitudes west from
d. Greenwich. and those west of the line
shall count longitude east from Green
witch. Thus Samoa is nearly $50 degrees
west of Greenwich, while the Fiji is
lands are nearly $50 degrees east. Yet
the islands are very near each other,
though the arbitrary line passes be-
tween them. AS a result, when it is
Sunday in Samoa it is Monday liz the
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