Nashville union and American. [volume] (Nashville, Tenn.) 1868-1875, 1871-10-28
REMEDY FoR EvzssAoF sEcsIl.Ahs
ClaAsqs N THk MAGNErIc ME.

magnetic poles. which are distinct and &C
cupy different positions on the earthls
surface from the terrestrial poles.
There are lines upon the eaEthis
surface called lines of no varia-
ton, where the needle points constantly to
ward the pole. Such line runs through the
center of Lake Erie ina northwesterly direc-
ton, nearer north than northwest On the
eastern side OF this line the needle rams to-
wards the west, and on the west side To-
wards the east, so that the variation in the
Eastern States Is westerly and in the West
em States easterly. This, variation under
goes regular changes IN the same direction
for long periods, and then returns, oscillat-
ing like a horizontal pendulum. ID the
Eastern States the north pole OF the needle
is moving westward at the rate of one
twelfth of degree aunnallys The yaria-
ton of the needle in London in 1862, was
nothing; in 1915 it was nearly 24s degrees.
Since that time II has been slowly tlecreas-
ing. These changes are called secular.
We give these facts to show the neeessi-
ty of referring all surveys made by a COM
pass TO the true meridian, unless the date
of the survey be given and a table of the
secular variation kept in the LEGALITY of the
survey. The last is not to be relied upon
in consequence of other changes to which
the compass is liable, which changes are
governed by no fixed or known laws. Such
are those which occur during the preya-
lenee of thunder storm, or when the
needle is in close proximity to
iron ore, or rock, or during the
appearance of the Aurora Borealis. There
is also a diurnal change, or daily
variation, the needle sometimes in north
ern hemisphere moving over an area of
from 10 seconds to Is seconds from eight
O'clock in the morning till two in the even
ing. There is also difference in variation
between summer and winter, being much
greater in summer. rI
With all these impediments in the way of
making an accurate survey, We do not won
der at the difficulties that practical survey
ors meet with in running old lines; neither
is it surprising that so many law suits and
disputes arise between persons owning con-
tiguous farms. When land was abundant
and cheap there was no necessity for such
great accuracy; but at present prices, and
when permanent rock and cedar fences are
being built, it is of the utmost importance
to the land owner that his possession be
fixed by something more constant than the
magnetic meridian. II is as shifty and rest
less as cloud, and operated upon by MI
merouS hidden and unseen forces. We
therefore thank Mr.. Trousdale for his
foresight in thus striving TO provide
against future litigation and vexatiOn.
The bill proposes in its first section that
the County Court in each county may, in
its discretion, have established at, or near
the county seat meridian line of one half
mile in length, the termini of which shall
be designated by planted stones with the
exact point on each stone marked with an
Y orotherwise durably engraved.
To this section two amendments are
necessary; one TO ensure the operation of
the law, and the other to provide for more
careful and accurate record of the variation
in the magnetic meridian. If the establish
ment of such line is left optional with the
County Courts, not six siIch lines will be
established in the whole State. The pub
lie mind does not run on questions of sci
ence, and however great the advantage to
be derived from it, and they are great, a
majority of the magistrates in the State,
unacquainted as they are with the
reasons for the establishment Of such
a line, viii be unwilling TO appropriate
money for that purpose. This is a case in
which the superior intelligence of the MEM
bers of the Legislature must go in advance
of public sentiment, and be willing to Shout
der responsibility in order to accomplish
great good. Were this line established,
and surveyors required to adjust their COM
passes by it, there would be no more con-
tentiOns about cOrners-the same line could
be run to-day and hundred years hence.
The second amendment We would sug-
gest, is TO have the distance of the stones,
not half a mile apart, as proposed in the
bill, but 57.3 chains Of four poles each, or
1922 poles. We will endeavor to explain
the reason for this particular length to the
unscientiic reader II line be run this
distance and another line varying from
the first by one degree be run the same dis
tance, the ends of the two lines will just be
one chain of four poles, or one hundred
links apart. If the lines vary
two degrees the distance between
the ends will be two chains
of four poles each, or two hundred links;
if the lines vary one-half degree, the termi-
nations will be fifty links, or half chain,
or two poles apart; in other words, the
length of the chord of the arc which sub
tends the angle will be one chain or one
hundred links for every degree. Now, the
advantage of this: A surveyor, wishing to
adjust his instrument, goes to the southern
stone. He runs a due north and south line
as indicated by his compass. When he gets
10 the end he has nothing TO DO to obtain
the variation but TO measure from the end
of the line run Ivy him to the other stone,
one hundred links for a degree and
place it Oh record, showing in such record
whether it goes so many links to the east
or to the west Of the stone. In this manner
the variation may be ascedained with accu-
racy to within one one-hundredth part Of a
degree. We have been tedious in this ex-
PLANTATION, because it is important that the
reasons he plainly understood why this par
ticnlar distance is suggested.
The other sections OF the bill make il
on the county surveyor TO exhibit
in the reports of his Surveys the amount of
variation east or west, and that he shall test
his instrument at least once in every six
months. Provision is also made for re-
cording every test inthe minutes Of the Coun-
Iv Court and il is also made misdemeanor,