Wessington Springs herald. (Wessington Springs, Aurora County, Dakota [S.D.]) 1883-1891, 1884-09-26
HOW SHIPS ARE NAyIGATED.

A"sS sA~~ ~ AAo ooiS nv oAs
Josephine Canning, in E~uan0dkst.
~- 49,
HOW SHIPS ARE NAYIGATED.
The history of navigation has been
sften written. Accounts of the inven-
ton and use Of nautical instruments are
accessible to any student who can refer
to an encyclopedia. But can the pas
senger 30 readily learn how the Captain
finds the way from Sandy Hook to Liv-
erpool? Can we reduce the science of
navigation to simple and easily under
stood statements? Erroneous impress
sions are current They are fostered by
sea tales and tourists journals. The old
sailor who knows every headland, the
pilot who has coasted along shore for
twenty years, are the popular types of
trusty navigators. So the musician who
plays by ear may dazzle an uSschooled
throngg. The expert hears but q series
Of brilliant blundcrs. Only the astist,
who counts every note, and measures
every rest, be certain of results.
Let us follow the voyage of a sailing
vessel. The first instrument used is the
mariners compass. By it, the master
takes the bearing of the last land seen;
he also estimates the distance, and calls
this his departure, including it in the
first days reckoning. His officers re-
cord every two hours the course, and
number of miles run. With variable
winds the ships progress will be like
that of a piece Of a cb~ecker-board, ex-
cept that the diagonal movements will
not be equal.
But a table gives the navigator the
northing, s%outhing, casting, or westing,
resulting from any given curse or dis
tance. He must reduce these to a
straight line. He takes the difference
between his progress north and the dis
lance made TO the south, and also be-
tween the casting and the westing.
Now, he knew Sandy Hook was sew
enty-four degrees from London. His
days work results in a departure from
that meridian of two degrees to the east
ward. Then, of course, he is but sew
enty-two degrees from London. Again,
he was yesterday justforty degrees north
of the equator. The distance sailed to-
ward the equator exceeds the distance
made toward the land by sixty miles, or
his difference of latitude is one degree.
Then, by dead reckoning, as we call
this process, he is in latitude thirty-nine
degrees north, and longitude seventy
two degrees west.
10 estimate the hourly progress, a
line is cast astern, marked in sections,
each proportional to the mile as the
glass (Which times the knots run out) is
to the hour. Or an instrument (called
a patent log) is lowed, the Roadway
tyrrinN vyh0n1c vpsth;, 1vhsoL ~oosko-
the distance sailed. In steamers the
speed is also computed by a gauge re-
cording the revolutions of the screw.
Yet it is quite impossible to keep a true
record of a ships run. Currents act
on her course. Her speed varies with
the minor influences. A careless man
may have the wheel. Therefore we
must find our position independent of
progress or point of departure. On
any day, out Of sight of land, we must
be sure just where the ship is. This we
a do, if the heavens are clear of
clouds, and our instruments are not in
error.
Latitude is simply distance from the
equator. When the sun is twenty de-
grccs north of this imaginary line, it is
summer. When he goes twenty de-
grees south of it, we have winter. This
is a real movement. He has another;
an apparent motion. He rises every
minute until noon, then recedes with
sunset. just before noon, the navigator
takes an instrument (seNtant or quad
rant) having a mirror at one end of an
arm, and at the opposite end an index
moving on an arc, marked into degrees,
minutes and seconds. The index, be-
ing fixed, must stop on this arc at the
altitude of the sun, if the operator
bring the reflected image to the horizon.
Noon passes; the reflected image ceases
to rise. 1t is necessary to apply small
corrections to the altitude observed. But
he allows for the impcrfection of his
s~cxtant, the height of his eye, the in
fluence of the atmosphere, as well as
the fact that he observed the edge of the
u and not the center, and finds the
suns true height is seventy-one degrees.
The basis of all calculation is that three
hundred and sixty degrees make a Cir
Gle. A qu~artcr-circle, the distance from
equator to pole, must, therefore, be
Ninety degrees. BY the altitude above
(scventy-onc degrees) the nlacks Just
nineteen degrees from being directly
overhead. If the day be July 20, a look
at the Nautical Almanac shows the suns
position (declination) to be twenty de-
grees north of the equator. 1t is nine
teen degrees from zenith to suns place,
and twenty degrees thence to the line,
Is it not then plain that their sun, thsr-
ty-nine degrees, is our distance from the
equator? This principle applies just as
well in winter. For the sun, warming
our Southern cousins, will rise on Janu.
AIRY 80 to about %thirty-one degrees. So
our ship would then be fifty-nine de-
grees from his position; twenty degrees
Of that space being south Of the line,
the difference, or thirty-nine degrees, is
our latitude.
Longitude is simply difference in
time. The entire earth's surface (three
hundred and sixty degrees) turns to-
ward the sur every twenty four hours.
Than his rays are directed on ono