The Wallace miner. [volume] (Wallace, Idaho) 1907-current, 1918-04-18

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a double reflection from two mirrors
used especially for determining lati-
tude at sea by taking the suns alti-
tude at noon"
The navigator begins to watch the
sun through the sextant near midday
and continues till the instant 1t begins
to descend. That is the instant Of
noon on the ship.
He then compares the height OF the
sun at noon with certain astronomical
tables in his chart room and knows
in what latitude the sun reaches that
precise height on that particular das
in the year.
When he gets his longitude he
knows exactly where his ship is, and
he gets this by thermometer.
Reward for instrument.
Early unsuccessful efforts were
made to SO adjust pendulum clock
that II would not be affected by the
rolling of a ship at sea, and In 1918,
by an act of the English parliament,
upon the recommendation Of COM
mittee OF which Sir Isaac Newton was
chairman, reward was offered,
G 100000, for an instrument that would
find the longitude at sea true to half
a degree.
John Harrison Of Yorkshire won the
reward after 43 years of study and
experiment. but did not receive his
final payment until 1764.
A navigator's chronometer Is ordi-
narily set to Green wich time. The
meridian line passing through Green
witch, England. where the British
royal observatory was established In
1875, is by common consent used as
the line from which time and distance
east and west, are reckoned.
For purposes of convenient compu-
tation, $50 lines Of longitude are COM
monty drawn from pole to pole and
starting from the Greenwich line. are
numbered east and west around the
world, the line opposite Greenwich. on
the other side of the world, OF Course,
being the one hundred and eightieth
degree.
Inasmuch as the earth revolves from
west to east, and inasmuch as 1t turns
through $50 degrees of longitude in "a
hours, II turns at the rate Of Is de-
grees an hour. Therefore, the time at
point $50 degrees east and west from
Greenwich would at the same time be
II hours later than Greenwich and IL
hours earlier than Greenwich.
For illustration, Samoa and the Fiji
islands are geographically neighbors,
but Samoa is nearly 1870 degrees west
OF Greenwich and the Fiji islands are
nearly 1870 degrees east of Greenwich,
so that when it is Sunday in Samoa
it is Monday in the Fiji islands.
To obviate this difficulty, an arbi-
trary line has been drawn upon the
map of the world down through the
Pacific near the one hundred and
eightieth meridian line, and it has
been informally agreed that islands on
the east side of this line shall reckon
their longitude east from Greenwich.
This line is known as the internation-
al date line.
To get the longitude of ship at
sea, the navigator, having found the
ships time. compares 1t with Green
witch time, and II he Is sailing east
or Greenwich he knows that the ships
time is earlier than Greenwich time
because the sun is over points east
first, and If he is sailing west OF
Greenwich he knows that the ships
time is later than Greenwich time.
For illustration. IL it is noon on a
ship in the Atlantic and the chron-
ometer shows that 1t is 1 o'clock at
Greenwich, the navigator knows that
his ship is Is degrees west of Green
witch. since Is degrees of longitude
equal one hour of time.
Setting Of a Watch.
! We get our standards of time from
the study of the stars. To the man on
the street the setting OF his watch Is a
trifling thing. but to set watch or q
clock involves the use of the most
delicate machinery of this mechanical
age. machinery which derives its ac-
curacy from the stars in their courses.
Now, IL your watch runs down you
set it by the nearest watch or clock.
! If you want 1t to be accurate, you set
1t by jewelers. regulator" But the
regulator" varies little from day to
day, SO that the sum Of its varitions
in week may be appreciable, and the
regulator" in turn must be regulated
by the astronomical clock.
Every observatory has an astronom-
ical clock, which is made as perfect
as human skill can make 1t.
1t must be mounted upon firm
foundation, subject as little as pos
sible to vibration. change Of temper
allure and barometric pressure.
But when made rs perfect as pos
sible, 1t has to be set and regulated by
observation Of the stars.
For these observations transit is
necessary. The transit is telescope,
the tube of which is firmly attached at
right angles TO a horizontal. axis the