The weekly intelligencer. [volume] (Lexington, Mo.) 1891-1901, 1893-02-18
A KNOT AND a MILE.
How H~avigators Compute DIstanc,
Dead Reckoning"

VIII you please explain the difference
between a knot and a mile?" WHAT'S
the meaning Of the term knot, as APP
piled to the great speed made by the
City of Paris?" SIS not the term knot
simply n unit for measuring the speed
of a vessel at sea, and has it anything
to do with the actual distance hat the
vessel makes in Il specific time?" These
are only some of the questions asked
by "a Subscriber, - Constant Reader"
and scores of others whose letters ar
rive by each mail and each requesting
a reply, some inclosinG a slip of paper
and an addressed stamped envelope,
some with stamps only and many
with neither stamps nor money,
the writers having no thought
that the answers to such correspond
ents involve not only expense to the
newspaper of employing persons to an
swer these letters, but there must also
be added the cost of stationary, post
age etc. Some writer's also neglect to
give their full names, others fail TO give
their address, SO that many letters can
not be answered. This latter class, no
doubt, charges the editor with indiffer-
ence, while the fault is entirely with
the writer who neglects to say to
whom and where the reply is to be
sent.
But what is the meaning of the word
''knot?' 1t is purely and wholly a
nautical term, having specific and di-
rect application to the speed and dis
tance made by n vessel moving in
water. The word knot is the
mariners term for u nautical mile, and
its use is really. derived from the log
line used by navigators of the
ocean when they wish to de-
termine the speed and the
distance that the ship has probably
sailed in a given time. The log line il
an important and a very necessary part
of a ships fittings; especially is this the
case when, for several days at sea, the
navigator is unable because of the sun
being hidden by clouds or thick
weather to get a peep at it with his
sextant, from which the actual position
of the ship is worked out. With the
data taken by u frequent heaving of
the log "a small block or section of
wood with a long line attached and
run hi from the stern of the vessel for
a specific umb of seconds) noting
the force and direction of the wind, the
possible currents, or other influences
acting favorably or against the progress
of the ship, the navigator is enabled to
calculate very nearly, in overcast or
foggy weather, about where his ship is
at any hour of the day. This is called
working out the position of the ship
by dead reckoning"
Everyone who studied the geograph-
ical table in his early school days will
recall hat part of the sing-song recita-
ton running like this: go 1-6 statute
miles or 60 geographical miles equal 1
deg. of longitude at the equator" Now,
the difference between a statute mile
and Il nautical or u geographical mile
is that the latter is about 500 feet
greater than the former. There are 60
geographical miles to each degree of
latitude, or to each degree of longitude
at the equator, which divisions of
miles are called minutes" in the nau-
tical vocabulary, hence the old saying
"a mile a minute" AS there are 800
dogs. or meridians of longitude, there
are 81, 600 minutes or miles in the entire
circumference of the world, at the
equator; and it has been mathematic-
ally determined that one minute-one
geographical mile-at the equatorial
circle is equal to 6,0SG.7 feet. But it
has been the practice of mariners not
to be too exact on small fractions when
measuring distance as great as u mile,
consequently the practice of defining a
l<nnf nv nautical pnila ng nn1,a1 ~ AZ non
feet instead of 6,0S6.7 feet, has been
generally adopted.
When the navigator desires to make
a Longtime by which to ascertain the
speed which his vessel is making
through the water, he follows the con
slant &, 1850. As the number of seconds
in an hour are to 6,OS0 feet so are the
number of seconds in the time-glass Ito
be used) for measuring the ships speed
to the number of feet in each unit of
measurement marked off on the log
line. II a half-minute Go seconds)
glass is to be used, the knots must be
made so feet 8 inches from each
other, and the number of these
knots which pass from the reel
over the stern while the san d is run
mug HUN IhC up Uulu W Juc lower
bulb of the glass is equal to the num-
Der Of knots or nautical miles that the
vessel would make in an hour, provid-
ing the same conditions for speed con
tinue. For instance, if the engines of
a steamship continue to make the
same speed during the hour,
or If the force of wind and
spread of canvass of a sailing vessel
continue the same, the number Of knots
on the line passing from the reel while
the sand is running through the 80
second glass, is as good an actual meas
prement of the vessels speed through
the water as could be obtained except
that the course should be measured by
an actual survey with instruments. If
1t was shown that the vessel was MAX
ing ten knots, she would cover ten geo.
graphical miles, or q little more than
~ land miles, or eleven and a half
times 1850 %, $50 feet being equivalent
to a land mile). Hence, to speak of the
City of Paris having made 525 knots Or
nautical miles in "a hours, she covers a
distance of 604K land miles, as COM
pretended in railroad distances, or a
rate of 25 land miles an hour, which is
faster than many railroad trains travel.
IN. Y. Tribune.