The daily union. [volume] (Washington [D.C.]) 1845-1857, 1856-08-30
DEPARTMENT NEWS.
STATE DEPARTMENT.

NEW
STATE DEPARTMENT.
Deuations of the Compass in The Irish CAanneL-We
have received the following highy-interesting letter in
reference the devaons Of the compass in the Irish chan
mel from a correspondent residing in Liverpool:
gave some time since the substance of statement
made by two scientific of Liverpool (who had been
appointed by the English board OF trade to inquire into the
attending the loss of emgrant vessel in
the Irish ehann to the effect that there were devatons
of the compass the Irish channel board of both wood
and vessels which could not be accounted for The
subject has continued to excite great interest among scen
tic and nautical men, and committee was some time since
of that committee has lately been published and seems to
of sufficient importance to be communicated to you
with view its being disseminated along with the pre-
vious before mentioned among American nav
gators and others interested in the navigation OF the Irish
channel Its Importance, in connexon with the sowage
of cargoes, scarcely be overrated.
The recent loss of noble vessel in the letter. refers to
the fine American ship Racer lately wrecked on the Ark
low bank, coast OF Ireland.
have heard it said with reference to the loss of the
Racer that ALL nearly ALL of the vessels wrecked the
Arklow and Backwater banks American, and believe
that such the remarkable fact The value of American
property annually lost those banks is enormous; and
what is remarkable STILL is that most of the vessels
wrecked have been commanded by Of established rep
utaton for prudence and SKILL and experienced in the
gaton of the Irish channel:
The accumulation Of small Compass Errors Wooden Ships
LIVERPOOL COMPASS COMMITTEE,
40 Tower-buildings East, May l5 1856.
DEAR SIR Some months since ventured to call your at
tenton the fact that while the variation in the Irish
channel between Wales and Ireland slightly less than
and quarter points of the compass the general
ce with shipmasters and pilots to allow two and
half points find by inquiry that in many this
allowance is still made and, in some instances even as
much two points and threequarters 1t will be easy
to show that though some courses such allowance
for compass may be quite correct is most unsafe
to attribute much TO variation and allow it on every
course
That the remarks about to make in eucdation OF
this and associated topics may be generally ntegi
BILE allow to explain that though persons the
pariaion Of the compass and deriaon Of the compass
If they Of the same meaning the wenformed sea-
makes great distinction between the two and for
the following The from variation arises from
the magnetic north not coincidng with the true north
and this affects point OF the compass to the same
extent the allowance for it. whatever be the direction Of
the ships head is always the at the place and
time 1t is quite independent OF the position of the ship
Not with deviation which is caused by iron on board
the ship and which varies in amount with her position
but in regular and simple thatis changes
easily be understood. On whichever side Of the COM
pass the disturbing is situated it will be that
the ship turns round the compass and alter their rel
alive bearings Let be supposed that the disturbing piece
or pieces of iron the stern aft Of the compass
then when the ships head Is north the disturbing
will be south when her head is east the iron will be west
and throughout the whole circuit taking in success
sion every possible horizontal direction. Now though
may conceive the disturbing TO exercise the
energy in each Of these directions does not act with the
leverage, with the mechanical advantage in
each and therefore does not produce the effect the
compass needle When its attraction Is in the drec
ton the needle when II is north south Of the
pass card DETECTION Of the needle produced When
acts right angles to the observed direction of the
die II the greatest deviation The general effect Of
iron, AFT and below the compass the case which
contemplang is this When the ships head bears north
there is turns eastery the IRON aft turns
westerly, and in north ATTITUDES attracting the north end
of the needle westerly deviation, Producing ts
greatest effect when the ships head bears east The deva
ton then decreases slowly at FIRST afterwards and
rapidly till her head is south, when again there is
The ship still turning round to the westward,
the disturbing iron is carried eastward and draws the
north end of the needle the cast producing
ery deviation, arriving at its greatest when the ships
head shows west and again decreasing until she regains
| her original position.
In few words we that iron aft and below the level Of
the compass produces westerly deyation-tha is takes
vessel to the W Of her course when her head is easery
and produces eastery deviation causing vessel to trend
to the gh Of her course when her head Is westerly To
the result yet briefly Its effect is always TO tax
the ship the north Of her and to the greatest
when her head bears due east west walk round
docks will show that many ships have considerable
Of iron In the position wehave supposed Without
venturng at present to estimate the amount Of It's action
merely ask you TO remember that with the ships head
westerly its tendency like too large allowance for
ration IL to take a vessel TO the right of her
But will also be by any who visits ship
ping that nine ont OF ten ships have long and more
less massive horizontal iron spindes connected with the
steering apparatus; in at higher and some
lower level than the compass card and proceed to
draw your attention to the action Of such bars upon the
compass Now these bars and in fact the fore and aft hor
zontal portion Of all the iron in the ship produces e.
feet which has been apty termed quadranta" flor the
that changes It's character in each quadrant Of the
compass and produces easerly deviation when the ships
head Is between N and f. westerly deviation when be
tween E. and S. eastery deviation again when the ships
head is between and W.. and again westerly In the
naming quadrant IL worthy Of remark that this devil
alton isndependen of locality and has the same effect al
/ the equator as at the pole.
As before viii not attempt to estimate the amount
Of this kind Of but only direct your attention to the
fact that In two quadran Of the compass 1t viii tend to
decrease and In the other two 10 aggravae those deva
tons which arise from iron situated aft and below the com
pass.
There Is another Of which must be mentioned
here though IL does not affect large number of ships
as the preceding l allude to the double pinnacle In
many where these used the compass placed
so close disturb each other and the result quad
ranta Of precisely the opposite kind to that arising
from fore and aft iron but like IT. alternately increasing
and decreasing the due to that Of deviation
which 6rst discussed.
These remarks convey but very imperfect idea Of the
compass question: they should be taken in the restricted
In which they given and illustrating the pos
sble accumulation Of small errors; but would protest
against their being received merely theoretical for they
the result of ample and practical experience Ny de-
Ia briefly state much may enable any one who
win give the subject little attention to understand the
OF the devsons likely 10 arise from the iron fittings
about the rudder and steering apparatus board wooden
ships When deviations occur in merchant ships,