Barton County democrat. [volume] (Great Bend, Kan.) 1885-1915, 1888-07-19
TIME AND LONGITUDE.
Why the Calendar Is Changed in Sailll
Around the World.


Around the World.
1t is known that in sailing around
the world, or even in sailing more
than half way around, the calendar is
changed upon crossing the one hun
dred and eightieth degree of longitude.
To understand the reason for this
change and how it is done, one will
find it helpful to imagine a particular
voyage such as will call for the MAX
ing of the change. Suppose, for in
| stance, we are at London about the
| Goth of March. At six o'clock in the
evening it is sunset. The half of the
globe west of the meridian line is
lighted by the sun, the half to the east
OF the line is in shadow. On the oppo-
site half of the meridian circle, that is,
on the meridian of one hundred and
eighty degrees, it is sunrise of what is
to be the next day at London. Now
suppose that at this hour of sunset one
| ship sets sail from London to go
! around the world eastward, and an
| other sets out for the same voyage
sailing westward. Let them make
equal speed and they will meet on the
one hundred and eightieth degree of
longitude. They carry each a chro-
nometer which keeps London time.
But the ships carry local time, and
this is corrected every day when the
sun is to be seen crossing the meridian
| at noon. The difference between local
time and London time is easily read
| in longitude east or west of London
| according as the local time is fast OF
slow of the chronometer, allowing
| four minutes difference of time for
one degree of longitude. We will now
suppose the speed of the vessels is
such that they will reach the one hun
dred and eightieth meridian, and meet
each other in just sixty days, and at
the hour when it is sunset at London.
Then again it is sunrise at the point
where the vessels meet. The ship sail
| ing east, that is, in the same direction
in which the earth turns, has gained
just twelve hours by going half wey
round the world, and this is the sun
rise of its sixty-frst recorded day. The
ship sailing west has lost just half a
day, and this is the sunrise of its six
tieth recorded day, though the time
has necessarily been the same.
Now if they were each to complete
the circuit of the globe. the ship sail
ing eastward will keep on gaining, and
will make another twelve hours in go
| ing over the rest of the way, so that it
would come to London at sunset of the
one hundred and twenty-irst day if
no change were made in it's calendar
| BY the chronometer it would be sunset
of the one hundred and twentieth day.
| On the other hand the ship sailing
| westward will go on losing as before.
On the first half of the voyage its local
time had fallen back from sunset OF the
| sixtieth day to sunrise of the same. In
completing its voyage it will fall be-
hind just the same, and coming to Lon
don at the same time the other ship ar
rives, its reckoning will show that it is
sunset of the one hundred and nine
teenth day. The difference between the
calendars of the two ships will be two
days, if no change is made; and neither
calendar will be correct. To make the
calendars tally with London dates it is
necessary that the ships sailing east
have its calendars set back one day,
while that of the other ship must be
set forward just as much. The place
for making this change is at the one
| hundred and eightieth meridian.
The ship sailing east is half day
ahead of London time. By calling its
sixty-irst sunrise the sixtieth, just
what the sunrise the morning before
had been called, we put its time twelve
hours slow, and this it will gain, and
come to port at the one hundred and
twentieth sunset. On the other hand
the vessel sailing west reaches the one
hundred and eightieth meridian at its
sixtieth sunrise. 1t is half day be-
hind London time. Call this sunrise
the sixty-first, and that will make its
time twelve hours ahead of London
time. This twelve hours, however,
will be lost on the rest of the voyage,
and the ship will come to port with the
other end of the one hundred and
twentieth sunset. BY this change of
the calendar as practiced, the local
time can never differ from London by
more than half a day, and as no less
| change than that of one entire day can
be made in the calendar, the method
described secures the closest cores
pondence between local time and that
of London, according to which We
reckon longitude Youths Companion.
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