The New Orleans bulletin. [volume] (New Orleans [La.]) 1874-1876, 1874-04-08
PRICE-FIVE CENTS
ERRORS OF THE COMPASS,


Magnetic Ne dl~-Wrccks W. icA were
Caa.ed by sDeviatiOns-Esow TO Cor
rect Them.
Captain Henry O. Cook, formerly of the
British navy, addressed the Polytechnic
Branch of the American Institute, New York
city, on the I'd inst, on deviations of
the compass. The audience included mauy
navigatOrs and scientific men The Captain
said Gas reported by the SUM- that it might
he supposed as matter of course that sea-
men generally would interest themselves in
the compass, but no body of men, as a rule.
were more ignorant of its workings. Thew
had ignored the science of the COMPASS "A
a subject too deep for contemplation. They
put their faith in the compass in fine wealth.
er, and were helpless in bad weather.
A few navigatOrs who had watched and
noted the variations Of the magnetic needle,
had learned to extract from its capricious
movements information which was yelled
and distorted by host of disturbing influ-
ences. The seamen who failed to seek such
information were excusable, for though very
able and scientific men had made thorough
investigation, they had failed to discover
the laws which govern the action of the
magnetic needle. The British Admiralty
manual contained facts and figures of more
use to the mathematician than to the prac.
tical navigators of our merchant marine.
Only five or six centuries ago had western
nations learned to use the needle, whereas
it had guided the Chinese mariner for thous-
ands of years. Nothing had been done, how
ever, in the way of attempting to correct
the errors of the compass by experiments
until the close of the last century. Capt.
Flinders was the first in the field and was
followed by others. Experiments only serv-
ed to shake confidence in the needle, and to
cause mariners to place their reliance on the
heavenly bodies. Capt. Flinders proposed
to correct the deviations of the needle by
compensation.
Capt. Scoresby, afserward the Rev. DR..
Scoresby, had done more than any other
man t" bring to public attention the devil
ations of the needle, and through the inves.
legations of Capt ScOresby and others
method OF compensation was generally
adopted, but it was imperfect. These inves-
LEGATIONS were on wooden vessels, aud when
iron came into use in ship building, other
experiments had to be made, and the previ-
GUS deductions were found to be of no value.
Subsequent experience had proved that
Capt. ScOresby was correct in saying that
iron vessels while building became charged
with magnetism, a portion of the magnetism
permanent in the vessel under all circum-
stances, and another portion which might
be called sub-permanent, which could be
taken from the vessel by violent strain
ing and knocking about" Twenty or
thirty years ago rules for the compensa-
ton of cOmpasses were compiled by Mr.
Airy, and the following of those rules had
undoubtedly caused some of the most terri
BILE shipwrecks. In the ship Tayleur of
1000 tons, which sailed from Liverpool with
a load of emigrants, the steering compass
deviated 60 degrees or five and half points.
The result was q wreck on the Irish coast
attended with fearful loss of life. The court
of inquiry unanimously attributed the dis
aster to the deviation of the Tayleur's COM
passes. Several iron vessels had been lost
of late, and hundreds of lives cut off. The
true cause of nearly all such wrecks was in
the compass, though some courts of inquiry
ignored this fact.
tiOns of DIR. ScOresby caused alarmed among
those who believed in the rules of Mr. Airy
and the compensation magnet.
Changes in the magnetism of iron vessels
added greatly to the complexity of compass
correction, and experience had proved that
it was not safe to rely on Airy's compensa-
ton magnets. A series of careful observa-
tions were made on different ships, and
tables of deviatiOns framed therefrOm.
These could not, however, be depended
upon. They were liable to change with
change of latitude to an extent which could
not be understood before the voyage. One
vessel was not guide for another. The de-
viations obtained with vessel in an up
right position would be altogether false when
a vessel was heelipg over either to starboard
or port, and the magnetic influences which
surround vessel could not be Obviated,
however carefully her tables Of deviation
might be made out. The fluctuations in the
magnetism of vessels could not De guarded
against without repeated observations to
correct the very tables of deviations on
which the navigator was to rely. Thus
there was the directive force of the needle
which becomes actually sluggish in its work
ings Commodore Jenkins, of the United
States Navy, had said that "neither com
pensatiOn nor table Of deviations could
lie relied upon, except in about the same
magnetic latitude as that in which the yes
sci was swung"
The Captain showed that seamen could
not place implicit confd' nee in their COM
passes when corrected by compensation,
and that the compass, when compensated.
would not act the same in fine as in rough
weather; when far from as when near land.
He added shat OH Thursday evening next
he would deliver another address on the
method of correcting deviations of the COM
pass.
DR.. s. V. C. Smith said that he had heard
Captain and Rev. DR.. Scoresby say that
there was no reliance to be placed on the
magnetic needle in storms. Mr.. Dudley
Blanchard remarked that it was we'll known
to surveyors that the needle deviated on
land, especially in the neighborhOod of iron
mines.
Capt. McDougal described an interesting
storm which he had encountered forty-fve
miles from Sandy Hook, when electric fire
streamed from every mast and spar, and his
compass was in utter disorder.
There is a ladies' cooking club in Boston,
the members of which aim at proficiency in
the management of their kitchens Meet
inQa are held every week and the ladies con-