West Virginia Democrat. [volume] (Charles Town, W. Va.) 1885-1890, 1888-06-29
this way day after day, the ships

position is known from Gay 10 uay--
or. in other words, those who have
her in charge thus find their way
from port to port. Theoretically
this is right; practically there are.
difficulties. The circumstances
which render "dead reckoning an
unsatisfactory method OF navigation
are unfortunately numerous.
The determination of the ships
course depends upon the indication
OF the magnetic needle. or course,
every one knows that the needle does
not point due north. True as the
needle to the pole" may do very well
for poetry, but it is about as far
from the truth as it can well be.
The needle not only does not point
to the pole in 999 places out of the
900 but it does not point in the
same degree or way from the true
north at different places; nay, its
direction is not the same at the
same place at different times. There
are parts Of the United States where
the needle points west of north, parts
where it points east OF north. In
England the needle points twenty
degrees west of north (nearly N.
N.-W). Twenty years ago the nee-
die pointed further west; two CEN
turies ago it pointed twenty degrees
east ofnorth (nearly N. N.-E). OBJ
servers can keep account OF these
mysterious changes affixed stations
but although our physical geog-
raphies give the magnetic meridians
for the whole earth at given times,
the position of these meridians is
not accurately known for large
part of the ocean (and even conti-
nents) at any time, and the changes
taking place are far from being &C.
curately determined, either as to
nature or as to rate.
Then the magnetic needle in each
ship. has its own peculiar peculiari-
ties. In different positions OF the
ship, the deviation of the ships nee-
die from the true position { for the
place where she is is different. II
she has been Swung, under proper
conditions before starting, the diff
ferent deviations for different posi-
tions may be determined; but some
times blows received at sea, great
changes of temperature, and similar
causes so far affect what may be
called the ships magnetism that
the deviations are changed from
those noted in port; and in such
degree the indications Of the needle
are thenceforth unsatisfactory.
Then further as to direction, It is
by no means an easy thing for
steersman to keep the ships course
exactly to that desired. To begin
with, the compass card is small. and
a deviation from the direction which
would make an important difference
in run of mile would be almost
imperreptible on the card. But
apart. from this it takes q good
steersman to keep ship steady on
any course. The momentary devia-
tlons this side and that may be
slight, but in the long run a measn-
rable deviation from the main
course may arise, which must be
regarded as distinct deviation
from the intended track.
Lastly Gas regards direction of
motion) every ship makes more or
less leeway--that is, besides advan-
cling in the direction of her length.
the only part of her advancing of
which the needle tells, she is car
ried sideways through the water
unless the wind is directly astern of
her.
Then as to rate OF motion, the log
affords the only means available for
determining the ships velocity.
Now there are different ways Of
throwing the log. The old-fashion-
ed way is to cast overheard q float
which will Immediately assume such
position in the water as to remain
appreciably still while the ship
passes OF; then by noticing how
much of the log line runs ont in
given time, we can form an opinion
as to the rate at which ship is
travelling at the moment. Another
form is a float which is not allowed
to travel from the ship-to speak
more correctly, which is dragged
along with the ship. The float is SO
constructed as to register the rate
which it is dragged through the
water. This may be done in vari-
GUS ways-probably the best is by
attaching screw blades to an axis
which is horizontal in the water and
parallel to the ships course-the
axis being free to rotate. and a rec
ord of the number of rotations in a
given time being provided). All
the methods available are, however,
rough. Moreover, ships speed is
not the same for ten minutes to-
gether; and the log ought to be cast
at least every five minutes to give
ANYTHING like an exact account OF
the progress she is making.
For al these reasons dead reck
oning" is untrustworthy. The cap
tain Of valuable ship, carrying not
only an important cargo, but valua-
BILE lives, will not trust if he can