The Lexington dispatch. [volume] (Lexington, South Carolina) 1870-1917, 1897-09-01
Z MfrEs AND KNOTS.
some Nautical Infoxnafion That Il Well
worth Remembering.

some Nautical Irfoxrnation That ID WeA
Worth Remembering.
Distances at sea are measured ID
miles, Just as they are on land, but the
speed of a ship at sea--that is, the
number of miles she makes through the
water in one hour of time-is measured
in knots. There is therefore difference
IN the meaning of the word mile and
.knot.' They are 10 more synonymous
than are the words distance and
@speed," to which they are correlated.
Tt IS we'll to. bear III mind, in speaking
or writing Of nautical matters, this dis
tipction-that mile is unit of dis
tance. but knot is unit of speed.
There are two kinds of miles-a statute
or land mile and nautical or sea mile.
A statute mile is 5, $50 feet long. 1t
is our standard of itinerary measure
adopted from the English, who in turn
adouted it from the Romans. A Roman
military pace, by which distances were
measured, was the length Of the step
taken by the Roman soldiers and was
approximately feet long. A thousand
of these PAGES were called in Latin
mile. The English mile is, therefore,
a purely arbitrary measure, enacted into
legal measure by statute passed dur
ing the reign of Queen Elizabeth. 1t
has no connection with any scale III
nature.
A nautical mile, on the other hand,
is equal in length to one-sixtieth part
of the length of a degree of great cir
Gle of the earth. But the circumference
of the earth is nowhere true circle. Its
radius of curvature is variable. Hence
the nautical mile, as matter OF fact,
depends for its length upon the shape as
we'll as the size of the globe sailed over,
and hence, strictly speaking, the length
of the nautical mile should vary with
the latitude, from 6,046 feet at the
equator to 6,l09 feet at the pole.
Such extreme accuracy IS not neces-
sary in navigating and cannot be we'll
attaiuedw undue labor. The Eng
lish admiralty, therefore, has adopted
G0ee feet as the ieEgtl Of a nautical
s.usiis, which corresponds with the length
Of one -sixtieth of degree, or ene min
ute of arc of great circle in latitude
4s degrees. The united coast survey has
adopted the value of the nautical mile
"as equd to one-sixtieth part of the
length of a degree on the great circle Of
a sphere whose surface is equal to the
surface of the earth.
This gives the length of one nautical
mile as equal to 6,0So.27 feet, which is
very nearly the value of the admiralty
mile adopted. in the English navy.
Practically the nautical mile is 500 feet
longer than the statute mile. In other
words, one nautical mile is equal to
1.1515 statute miles, or one statute
mile is equal to 0.S69 nautical mile.
Multiply nautical miles by 1.i5l5 and
the product will be statute miles, OF
multiply statute miles by 0.S6a, and
the product will be nautical miles.
A knot is in length nautical mile
that is, $3.50 feet. But it never, cor
rectly speaking, meaDs anything more
or less than pantical mile an hour.
When saying that 4 ship has speed Of
20 knots, it means that in one hour OF
time she can go 20 nautical miles, pre-
cisely in the way that 2:40 horse
means that horse in minutes and &c
seconds of time can trot one mile. Re
member, then, that it is erroneous tt
use knot as synonymous with mile; So
too, is it an error to say so many knots
am honr-for the word knots alone sig.
nifes the time as we'll as the rate Of
progress of the ship during the time.
Another point to bear in mind is that
though the measure of distance at sea ii
called, like the measure of distance on
land, a mile, yet distances at sea are