The morning news. [volume] (Savannah, Ga.) 1887-1900, 1896-07-02

and Untiring Calculation.
From the Philadelphia Record
The earliest knowledge Of the earth's
,nagnetism. or the fact that the earth
acts as huge magnet. dates from about
rhe thirteenth century, when one Marcus
Paulus. a Venetian. on returning from
a voyage around the then known Worlu
brought back with him the hrst COM
pass seen in Europe, he having learned
its use from the Chinese. The chinese
however. claim to have used the com
pass many Years before Christ Inc
popular knowledge of the earth's magnet
ism consists in the one fact mat the
pole of a compass needle marked North
or with an n points to the geographical
North Pole, and even this is erroneous
since the compass needle only points ap-
proximately to the North Pole. The earth
acts exactly as a huge magnet having
two poles just like any other magnet
a North Pole and a South Pole. The earth
magnetic poles are situated approx
mately near the geographical poles OF the
earth. the magnetic pole being situated
near Bafhn's bay, about thousand miles
south Of the geographical North Pole.
in latitude 10 degree and Longitude 30 de-
Thus it will be seen that when IL is sta
ted a magnetic needle points to the North
Pole, or due north, il is understood 10 pc
only approximately north. Such needle
points in reality, to the magnetic poles,
and hence at almost all points OF the
earth's surface it will point either east or
west of the true north. All points OF the
earth at which a magnetic needle does
point TO the true north may be connected
by two comparatively regular lines run
ming north and south, one in each hemls-
phere The one in the western hemisphere
in the United States, passed, IN lS50
through South Carolina, Ohio and Michi-
gan.
Lines connecting points having the
same deviation from the true north and
south are called isogOnal lines, and are
plotted on maps called declinauon charts.
Deviauons from the true north may be
either east or west, and are measured in
degrees.
If a compass needle be suspended, so
as to be free to move in perpendicular
direction, Ii will come to rest IN a slant
ing position, obliquely to the surface OF
the earth. This deviation from hori-
ZOntal position is called the inclination
of the needle and is also measured IN
degrees. The inclination of the mag
netic needle varies in different parts OF
the earth, being greatest and practical
ly perpendicular directly over the mag
netic poles. and decreasing as the mag
netic equator is reached, at which place
the needle will be horizontal. Crossing
the needle will begin to dip in a SINH
lar manner, increasing in amount until
the other pole Is reached, when 1t will
again be perpendicular. Owing to this
tendency to dip, magnetic needle is not
usually supported at its center of grav-
ity, but at point where the dip is COM
pensated for by the greater length Of
that end Of the needle, The earths
north magnetic pole is situated in the
southern hemisphere, and the eartn's
south magnetic pole in the northern
hemisphere. 1t is well known that the
opposite poles of magnets attract each
other, hence the north pole of the mag
net is attracted toward the north pole IN
the direction Of the geogranhiF g. 49,
pole for a similar reason. The val b OF
the inclination of magnet neeq,N is
plotted on a chart, called a declikItion
chart, on which lines connecting Iees
of equal isoclinal lines. Besides tine
phenomena of the earth's magne SIN,
represented by the inclination and de-
clination of magnetic needle, the is
stu another; that is, the intensity oKthe
magnetic force at any point on the
earth's surface, being greatest at the
magnetic poles and decreasing gradually
until the magnetic equator is reached,
points on the earth having the same
magnetic intensity are called isodynamic
lines.
Another interesting phenomenon of the
earth's magnetism is that each of these
three characteristics are constantly
changing their values. In order to ascer-
tain the character and extent of these
changes, buildings called magnetic obser-
vatories are established at widely separa-
ted points, usually in connection with
astronomical observatories. By means of
Photographic records made by continu-
ously measuring Instruments rontinu
Gus record of all changes is obtained
inese variations may be classified as
gaiy changes, or those taking place at
inherent hours of the day; annual varia-
uons, or those which occur at different
tunes Of the year; secular variations. or
those which occur at considerable inter-
vans or time, and irregular variations or
snUse accompanying so-called ma ghetto
Sums Olufnal and annual variations
are or practically small Importance a :
are also the transient, irregular varfa-
tions. BY far the most important are the
neat ~ o vaIl1llohs. which apparently re-
Pedt themselves in periods of about 32O
SedIS' very little is known about them
as YET. An example, however. NAV he
49, IN, III the case OF London, where rec
oros nave been kept for a period extend
ing Tar back These show that in 1850
Oh SHe uechnation at London was II degrees
% minutes east, while in 1850 The deeli-
nation was zero, the needle pointireg dua
north and south. In 1915 the naeIIs 1oS
1SdHl attained its maximum westerly de-
S!IndLon amounting to "A degrees "a min
rteS; II then returned towards zerb and
north and south
II Is now generally conceded that aurora
Pnenomena are of electrical orjrif ac-
t"J MS til6 ueNel0pment of uyausJIa1
electrical discharges in the air ~ ~ a.
t tbe IN sne prevalence Of these auroras that
in r SqI- ia, ed magnetic storms occuE dur
tvs ~Illch time comparatively strong cleo
s a,J earth currents are developed which
ffiE nn disturb telegraphic communica-
r, hkact information as to changes in
10 shetc declination are Important both
10 tne mariner and to the SURVEYOR The
a Tt'er' Tor instance, is plotting out an
80 OF ground according to diractions
ag +o''e en-, perhaps, several hundred wears
az az So nnds that a certain line runs saw,
o. uegrees west from given point thirty
$50 west, as indicated by mis- iostrn.
t ~ NJ now: however, does not corresnond
in t ne original direction. owing to changes
4" We we earth's declination at that noinf
nile the mariners commas is No
c Sgse e3lely relied upon to furnish the
Vet the go Salnng on ocean-going vessels,
yyoea one general course is directed nv 4ts
emninr,oaI ne large amount of iron now
vessels as IN Ine construction of modern
cbine.s, as Wen as the massive trf,1 ma
the ird, employed produces variations in
which beSie IONS Of the compass needle
N.iCH nave to be cofnrereo4a5 ~