San Antonio daily light. [volume] (San Antonio, Tex.) 1886-1907, 1897-03-01
TIE Daify tiqGt
MONDAY, MARCH l. 1897.
KNOTS AND MILES.
Difference Between Them Explained for
the Benefit of Landsmen.

the Benefit of Landsmen.
In this day of record-breaking by
ocean steamers, when every big steam
er that comes into port is expected to
AIRY a record hung at yardarm, so to
speak, how many landsmen know the
meaning of the term knot" in which
rate of speed at sea is chiefly expressed?
1t is purely and wholly a nautical term,
having specific application to the speed
and distance made by a vessel moving
in the water.
The word knot is the mariners
term for q nautical mile, and it's use is
really derived from the log line used by
navigators of the ocean when they wish
TO determine the speed and the distance
that the ship has probably sailed in a
given time. The log line is an i'm
the ships fittings. Especially is this
the case W hen, for several days at sea,
the navigator is unable, because of the
sun being hidden by the clouds or thick
weather, TO get peep at itwith his SEX
-s1t- from which the actual position OF
IL ship i worked out. With the data
-a6El bE a frequent heaying of the log
d small block or section of wood with
: Lung line attached and run out from
IL t1S-1 Of the vessel for a specific
zU-bsr Of seconds, noting the force
and direction of the wind, the possible
currents OF other influences acting IA
VoTeblv or against the progress of the
ship. the navigator is enabled to cal
cula;e 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"
Everyone who studied the geograph-
zeal table in the early school dayswiu re-
call that part of the sing-song recita-
ton running like this: "Sixty-ninc
and one-sixth statute miles, or sixty ge-
Ographical miles, equal one degree of
longitude at the equator" Now the diff
ference between a statute mile and a
nautical or geographical mile is that
the latter is about SOC feet greater than
the former. There are GO geographical
miles to each degree of latitude, or to
each degee of longitude at the equator,
which divisions of miles are called
minutes" in the nautical vocabulary,
hence the old saying, "a mile min
ute" As there are 300 degrees, or
meridians, of longitude, there are 81
600 minutes, or miles, in the entire cir
conference Of the world at the equator;
and 1t has been mathematically de-
termined that one minute-one geo
graphical mile-at the equatorial cir
Gle is equal to 6,OS6.7 feet But it has
been the practice of mariners not to
be too exact on small fractions when
measuring distance as great as a mile,
consequently the practice of defining
knot or nautical mile as equal to 6,OsO
feet, instead of 6,Os6.7 feet, has been
generally adopted.
When the navigator desires to make
logline by which to ascertain the
speed which his vessel is making
through the water, he follows the con-
slant 6,0S0. As the number Of seconds
in an hour are to G,OSO 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 If half minute go secunds)
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 knots or nautical miles
that the vessel would make in an hour.
providing the same conditions for speed
continue.
For instance, if the engines of n
steamship continue to make the same
speed during the hour, or if the force OF
wind and spread of canvas of sailing
vessel continue the same, the number Of
knots on the line passing from the reel
while the sand is running through the
3o-second glass is as good an actua,
measurement of the vessels speed
through the water as could be obtained
except that the course should be meas
ured by an actual survey with instru
ments. If it was shown that the yesse'
was making ten knots. she would cover