, 1877-01-20
Compass Variations.

llt ll'lAltt III llIN Nlh AN'llNli ~ l'Ai' - WV
seryutions were made in England anal
FcaNCc. which fNlly proved that the nee
lie pointed to the Eastward Of the true
north. The quantity of the variation
may he found by observing with Il COM
rnss. the bearing OF any celestial object
when in the horizon, (or as it is called,
thc magnetic amplitude y the di ference
between this and the true amplitude is
found by calculation, and will be the va
ration.
Some years after the discovery of the
variation, it was found that it did not
remain constant for the castcrly varia-
tion. observed in England. gradually lie.
creased until the needle pointed to the
true north, and then increased to the
westward, and is now about "a deg.
Therefore all the courses steered or
rraversed by compass must be correct
I'd for q variation to obtain the true
course to make this allowance you
must look towards the point of the com
pass you are travelling and allow the Va
ration from it toward the right hand if
'he variation be east ; but to the left
hand If west. The variation differs in
different places, and in the same place at
different times. 1t is well known that
any iron substance has an influence upon
the magnetic needle, and as the earth, in
certain spots, contains-near its surface
Iron or other minerals which attract
the needle, it will frequently happen
that it will point wrong. When needle
is well magnetizcd, the inside of the
cape smooth, and the center pin nicely
pointed, the needle will traverse lively
and long; but before 1t stops at the
true point, will have M almost imper.
ceptible tremulous motion. When the
needle settles quickly, hy giving the com
pass a light rap, it will commonly move
little this is II certain evidence that
something is out nf order When a com.
pass is ont Of use, it should be placed
where it can have no motion, and the
needle should be lett on the center pin :;
by keeping its polarity, the magnetic
power of the needle will strengthen rath.
er than weaken.
There is one line around the globe on
which there is no variation the general
course Of this line, on this side of the
globe, is from northwest to southeast ;
but it is crooked and irregular in its
course this line is not stationary, but
is ever changing its position, and not
withstandlng the great variety of its di.
rection, il never crosses itself. Accord.
ing to Holly's chart, made in 1900, this
line crossed the meridian of Greenwich
in 55 deg. south latitude, crossed the
equator 10 II deg. west longitude from
thence by various windings to the island
OF Bermuda; thence nearly west
course, until it struck the Continent near
Charleston, South Carolina. In 1855 an.
other chart was made, when the line had
falle" as far to the west, that it struck
the Continent near the coast of Florida.
On the east side Of this line the needle
points to the west of north and regu.
lar increase Of either east or west, decli.
nation is found from it on opposite
sides.
The line of no variation now runs
through Pennsylvania, and through the
eastern part of Virginia and North Caro-
lima, and leaves the coast at Cape Hat
teras.
Notwithstanding the utility of the
needle, il cannot he relied on when great
accuracy is required, on account of the
Irregularities to which it is subject, viz :
its annual and diurnal variations and To-
cal attractions so when an old course 10
given to find or renew a line, it cannot
be depended on. on account of the
change in declination. The annual mo.
tiOn Of the needle has not been uniform.
ally steady. In some years it is more
rapid than in Others, and in one or two
instances, ter period OF three or four
years, none except the diurnal motion
could Le discovered. Tho west declina.
tin is still Increasing.
No annual rate can b. fixed on as q