Seattle daily post-intelligencer. [volume] (Seattle, W.T. [Wash.]) 1881-1888, 1883-02-20
CAIsE OF Tine Loss OF
THE TACOMA.
Ed. Posr-IsrKLLlaKScER

PROBABLE CAIsE OF TnE Loss OF
TnE TACOMA.
Ed. PosT-INTELLIGESCER
If is is not too late to give the follow
ing views of the probable cause of the
steamship Tacoma, hope that you
will publish them, not only as bearing
upon the loss of the Tacoma. but as q
word of warning to officers serving on
board of iron vessels. The mariners
compass, the instrument most used and
least understood in the navigation of a
vessel, is subject to many changes from
its true magnetic bearing, that il re-
Quirss all the careful attention of the
officers TO watch and note these changes.
and no person in charge Of a new iron
vessel should ever place implicit con-
fidence IN the compass. 1t is not my
intention to raise any needless alarm
upon that subject, but merely to point
out the reflections that the needle is
subject to from the following causes:
First-Change of the local deviation"
m the compass. Second-Atmospheric
influence. Third-Local attractions.
Fourth-The loading of different car
goes, &c.
First-local deviation-after a vessel
has been launched and ready for sea
she is taken to a place used for such
purposes and swung several times to all
points of the compass, the bearings of
we'll known distant objects are observed;
afterwardithe bearings of the ships SOM
pass are compared with the well estab-
llshed bearings and tine difference
noted. a table is computed and furnish
ed to the commander, called the table
of Local Deviation" which would
serve all the requirements of navigation
II these deviations remained permanent,
but it is found that they do not retain
their permanency from the following
causes: The iron plates of which the
ship 10 built has received a certain
quantity of magnetism through the
rolling and hammsring to which thew
were subjected in forming to make the
hull, and again there are several thous
and rivets being made of malleable iron
struck with highly tempered steel ham,
ners, become highly magnetic that will
gain or lose this magnetism according
to atmospheric changes, for during GER
tain winds, fOgs, or magnetic storms
this magnetism in the plates and riyets
will be intensified, detrimental to the
true working of the compass. So great
an influence does the iron in the hull of |
a ship act upon the compass that it NAV
be told years afterwards in what direc-
ten the keel was lying at the time of !
building; and again the magnetism of |
oompasses may be affected locally by |
being in the vicinity of land containing |
iron ore; the compassos may be mater !
tally deranged by various cargoes and |
the distribution of weight changing the /
center of gravity.
The foregoing is a brief summary
which will be understood by those who
claim any knowledge of the magnetism
Of the mariners compass; but there are
defects that can only be overcome by
the careful and scientific attention OF
those in command, for when a master
has received his tabulatsd form of er-
rOrs, he should consider that these or
rOrs were found in fine clear weather,
when the ship was lying in smooth
water, how different must the cOndi-
tons be when she is under steam, roll
ing and pitching in a seaway when her
center of gravity Is constantly changing;
it Is possible to make small error in
his compass yet it becomes very formid-
able IN the navigation of a chip. We
will take the loss of the Tacoma for an
example. After leaving the Eastern
States her course was generally in a
sOutherly direction, having to pass
through a region of heated atmosphere,
therefore the compasses would have a
to be magnetiZed in that di-
rection; after passing through the
Straits OF Magellan her course would be
in a northerly direction, which would
tend to magnetic the compass in that
direction. The question is did the mas
ter of the Tacoma, after arriving in San
Francisco, use all endeavors to find If
the compass had changed from the table
of local deviation that had been re-
ceived; did he note any errors by the
cross bearings of head lands, etc., while
the Sound?
l sailed In a large iron steamer from !
New York to San Francisco, and l found !
that the local deviation had changed |
three different times upon the passage,
which / attributed to the foregoing |
causes. have no doubt that some will |
scout at the foregoing, but let them |
study and remember that tho earth |
itself is magnet ever varying, as sci
ence has demonstrated that the spots |
upon the sun and magnetic storms upon |
the earth have some connection with
each other, and what is the cause of the |
ever changing variation of the compass
upon the earth's surface.
Nearly all writer's and explorers have
pointed to some region in north latitude
NOON the earth's surface as containing
the magnetic pole, but have no doubt
that science will yet prove that the mag
netic pole is situated in the atmosphere |
corresponding in latitude to the earth's |
polar axis. For, we may say, what |
keeps the earth and all the planetary
bodies revolving around the sun but
magnetism? A magnetic band or belt
passes from the sun to and around the
earth, there is q reciprocal action from
the earth to the sun, the Garth at the
equator is revolving at the rate of 800
miles an hour, this rate of revolution is
decreased until it reaches the polar axis
where it is nil. So We have this mag
netism thrown off rapidly from equator
to the poles where there will be ON ac-
emulation of the magnetism, and
think that will account for the hidden
mystery of the polarity of the mariners
compass. So We can see why atmos-
phsric and other inf fences 10 y all tend
to derange the compass.
! read where strong northerly currents
are mentioned as being one of the prob
able agents causing the loss, but can
scarcely think that was the major cause
from the reports thatI read.
can only add that officers in charge
of the deck should several times during
the watch, when practicable, take the
bearings of the north star, as it is twice
in the twenty four hours due north and
is never more than one degree and a
half out of that bearing, which would
always be check upon any great errors
in plss after the variation has
bscn applied. JOHN BELL.
SAMIsH, Feb. IL, 1888.
The Northeastern LuInbernsan says
that between taxes, fires, winds and in
terest ON the money invested, it costs 10