Chicago eagle. [volume] (Chicago, Ill.) 1889-19??, 1893-02-04
A KNOT AND A MILE.
How Navigators Compute Distance
s.Dead Reekoning.v

''Nill you please explain the difference
between knot and a milel' "What is
the meaning of the term knot, as applied
to the great speed made by the City Of
nris!' SIS not the term knot simply a
unit for measuring the speed of vessel
at sea, and has it anything TO do with the
actual distance that the vessel makes il
a specific time" These are only some of
the questions asked by "a Subscriber,
Constant Reader" and scores of others
whose letters arrive by each mail and
each requesting reply, some inclosing
slip OF paper and an addressed stamped
envelope, some with stamps only and
many with neither stamps nor money.
the writers hav ng no thought that the
answers to such correspondents involve
not only expense to the newspaper of
employing persons to answer these letters,
but there must be added the cost of sta
lionery, postage, etc Some writers also
neglect to give their address, so that
many letters cannot be answered. This
latter class, no doubt, charges the editor
with Indifference, while the fault is en-
tirely 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 direct
application to the speed and distance
made by vessel moving in water. The
word knot is the mariners term for
nautical mile, and its use is really de-
rived from the log line used by naviga-
tors of the ocean when they wish to de-
termine the speed and the distance that
the ship has probably sailed in given
time. The log-line is an important and
very necessary part Of a ships fittings;
especially is this the case when, for sew
eral days at sea, the navigator is unable
because of the sun being hidden by
clouds of thick weather to get peep at
it with his sextant, from which the ac-
tual position of the ship is worked out.
With the data taken by frequent heav
ing of the log "a small block or section
of wood with long line attached and
run out from the stern Of the vessel for
a specific number Of seconds) noting the
force and direction of the wind, the pos
sible currents, or rather influences acting
favorably or against the progress of the
ship, the navigator is enabled to calcu
late very nearly, in overcast or foggy
weather, about where his ship is at any
hour of the day. This is called : work
ing out the position of the Ship by dead
reckoning"
Every one who studied the geographic
cal table in his early school days will
recall that part of the sing-song recita-
ton running like this: 80 1G statute
miles, or 50 geographical miles equal
one degree of longitude at the equator"
Now, the difference between statute
mile and a nautical or geographical mile
is that the latter is about S06 feet greater
than the former. There are 60 geograph-
ical miles to each degree Of latitude, or
to each degree of longitude at the equa
tor, which degrees of miles are called
minutes" in the nautical vocabulary.
hence the old saying ga mile a min ute. :"
As there are $50 degrees or meridians of
longitude, there are II, 800 minutes or
miles in the entire circumference of the
the world, at the equator; and it has
been automatically determined that one
minute-one geographical mile-at the
equatorial circle is equal to 6,086. feet.
But it has been the habit Of mariners not
to be too exact on small fractions when
measuring distance as great as a mile,
consequently the practice of defining a
knot or nautical mile as equal to $3.50
feet, instead of 6,08j.7 feet, has been
generally adopted.
When the navigator desires to make a
log line By which to ascertain the speed
at which his vessel is making through the
water, she follows the constant $3.50 AS
the number of seconds in an hour are to
6,0S0 feet 50 are the number Of seconds
in the time glass TO be used for meas
uring the ships speed to the number of
feet in each unit OF measurement marked
off on the CLINE. If half minute go
seconds) glass is to be used, the knots
must be made 20 feet inches from each
other, and the number of these knots
which pass from the reel over the stern
while the sand is running from the top
bulb to the lower bulb OF the glass is
equal to the number of knots or nautical
miles that the vessel would make in an
hour. providing the same conditions for
speed continue For instance, If the en-
gines of a steamship continue to
make the same speed during the
hour, or. if the force of wind and
spread OF canvas # sailing vassel con
tinue the same, the number of knots on
the line passing from the reel while the
sand is passing through the 30-second
glass, is as good an actual measurement
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 it vas shown
that the vessel was making ten knots,
she would cover ten geographical miles,
or a little more than ia land miles, OF
eleven and half times j.2S0 $3.50 feet
being equivalent 90 a land mile. Hence,
to speak Of the City Of Paris having made
j2j knots or nautical miles In 81 hours,
she covers a distance OF COLI ,aud miles,
as cOmprehcudcd in railroad distances,
I or % rate of - land miles an hour, which
is faster than many railroad trains travel
IN Y Tribune
RELIABLE RECIPES.