The morning news. [volume] (Savannah, Ga.) 1887-1900, 1892-12-31
A KNOT AND a MILE
How Navigators Compute Distance.
Dead Reckoning"
from the Nero Fork Tribune.


From the Netv York Tribune.
''Will you please explain the difference
between a knot and mileg" What is the
meaning of the term knot, as applied to the
great speed made by the City Of Parish sis
not the term knot simply unit for measur-
| ing the speed of a vessel at sea, and has it
anything 10 do with the actual distance that
| the vessel makes IN q specified timer 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 inclosinR
a slip of paper and an addressed stamped
envelope, some with stamps only, and many
with neither stamps nor money, the writers
having no idea that the answers to such cor
respondents involve, not only expense to the
newspaper OF employing persons to answer
these letters, but there must also be added
the cost OF stationery, postage. etc. Some
writer's neglect to give their full name
others fail 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 entirely
with the writer, who neglects to say 70
whom and where the reply is to be sent,
But what is the meaning of the word
"knotf' 1t Is purely and wholly a nautical
term, having specific and direct application
TO the speed aud distance made by a vessel
moving in water. The word ''knotn is the
mariners term for nautical mile, and its
use is really derived from the log line used
by pav1gators Of the ocean when they wish
to determine the speed and the distance that
the ship has probably sailed in given time.
The log ineis an important and a very nee
essary part OF 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
,.ef - 49,,
the actual position OF the ship is worked
out. With the data taken by q frequent
heaVinR OF the log Ia small block or section
OF wood with long line attached and run
out from the stern Of the vessel for a specific
number OF secon1sl noting the force and di-
recEion Of the wind. the possible currents,
or other influences acting favorably or
against the progress OF the ship, the nav
igator 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 geographical
table in his early school days will recall
that part of the sing-song recitation run
ming Ike this: "69 Is statute miles or 80
geographical miles equal one degree OF
longitude at the equator" Now the differ
ence between a statute mile and nautical
or geographical mile is that the latter is
about 500 feet greater than the former
There are so 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 nauti-
cal vocabulary, hence the old saying "a
mile a minute As there are $50
degrees or meridians of longitude, there are
81 800 minutes or miles 10 the entire circun-
ference of the world at the equator; and it
has been msthematicAlly determined that
one minute-one geographical mile-at the
equatorial circle Is equal to 6,086.7 feet.
But II has been the practice of mariners
not to be too exact on small fractions when
measuring distance as great as q mile, con-
sequentlv the practice OF defining knot or
nautical mile as equal to $3.50 feet instead
of 6,0S6.7 feet has been generally adopted.
When the navigator desires TO make
| log-line by which to ascertain the speed
which his vessel is making through the
water he follows the constant 6,0S0. As
| the number OF seconds in an hour are to
| $3.50 feet 30 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 80 seconds glass is to be
used, the knots must be made so 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 these 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 speed of canvas 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 thirty-second glass, is as
good an actual measurement of the yes
sells speed through the water as could be
obtained, except that the course should be
measured by an actual survey with instru-
ments. Ii II was shown that the vessel was
making ten knots, she would cover ten geo.
| graphical miles, or a little more than H.
land miles. or III times !, 2S0 $3.50 feet be-
ing equivalent to land mile. Hence, to
speak OF the City OF Paris having made SOS
knots or nautical miles in twenty-four
hours. she covered distance of 6041 land
miles, as comprehended in railroad dis
tances, or rate Of 25 land miles an hour,
which Is faster than many railroad traius
| travel