Rock Island Argus. (Rock Island, Ill.) 1893-1920, 1899-02-18
A SERIOUS PROBLEM.
THE COMPASS AND THE GROWING
USE OF ELECTRICITY.

less to the Mariner and the Sur
NeyOr-A Curious Discovery.
Although the invention and introduc-
ton of the trolley system of street rail
ways have been Of inestimable value to
civilization it has incidentally wrought
some harm here and there. Emphasis
was laid on one of these draw backs to
electric traction in the address delivered
by Professor 4. w. Rucker at a recent
meeting Of the British Association For
the Advancement of Science.
Ia various parts of the world observa-
tories have been established for the pur
pose CT keeping track of the changes in
the direction in which the magnetic
needle points 1t was long ago discov-
cred not only that the compass does not
aim directly at the north pole, but that
the amount Of variation IN its iEdica-
tions from true north undergoes slow
alterations. Hence it is necessary to
mako fresh charts, showing the varia-
ton for different parts of the globe
every few years. But in order to get
the data for such corrections-of the
highest Importance to the surveyor and
mariner-it is requisite that careful OBJ
servations he made continuously at q
number of widely separated points.
Two of the most famous and hitherto
useful institutions of this class are stu
ated in Washington, in the grounds of
the naval observatory and in Toronto.
The interference of the electric currents
that run through the earth and the
track Of trolley lines which have been
constructed near these observatories in
terfere so much with the behavior of
the Instruments of both places that the
records now obtained are practically
worthless. And the experts are greatly
puzzled by the problem of escaping from
this vexatious interruption of their
work
So delicate are the influences which
the magnets in such an observatory are
intended to investigate that they can be
perceived only when the apparatus is
most scrupulously guarded. The room
in which they are mounted is under
ground. Visitors are never admitted ex-
cept under unusual circumstances and
are required to deposit their jackknives,
keys and all ether metallic objects about
their persons before entering the apart
mept. The magnets, generally bars of
above scale that is graduated to the
most minute fractions, and a telescope,
On an adjacent pillar, is used to read
the fluctuations, which are too small to
lie disceInibIe by tho unassisted eye. A
tiny mirror, as big as dime, catches
beam of light mere slender than the
lead in Il pencil and reflects it away to
Z sheet of slowly moving Photographic
paper, on which permanent record is
made. The arrangement of the apparatus
is such that the movement Of the mag
net is mngnitied many times in the rec
ord, in order 20 render tho changes per-
ceptible.
There arc three sets of instruments
on duty in such an observatory One
swings horizontally, like Il mariners
compass. Another dips up and down.
a third is designed 10 measure the in
tensity of the earth's magnetism, which
is separate thing from the direction
in which it acts. And so sensitive are
they that their readings are apt to ha
interiered with by exceedingly trivial
causes. 1t is customary for the superin-
tendent to inscribs on the scroll Visit
ors admitted, whenever such u breach
of the regulations is permitted, so that
if any abnormal fiuctuGtion is detected
in the motion of the magnets a suspicion
of its meaning will be excited in the
mind of the scientist who afterward ex-
amines the Photographic trace.
In spite of the delicacy of the appa-
ratus. it may seem surprising to the ley
mind that the passage of trolley cur
rents at distance of many rods from
the observatory should be able to affect
the instruments within. But they do,
and it is impossible to separate in the
record the variations produced by genu-
inc changes IL terrestrial magnetism
from those which are caused by the
trolley. Professor Rucker said few
DAYS ago: From all parts Of the world
we hear Of observatCries ruined or
threatened by the invasion of the cleo
trical engineer. Toronto and Washing
ton have already succrmbed, Potsdam,
Pare St. Maur, Greenwich and Kew are
besieged, and the issue largely depends
Ipon whether these great national OBJ
servatories can or cannot make good
their defense"
Although the practical service to
which is rendered by institu-
lions of this class is alone sufficient to
justify their maintenance and to war
rant alarm as to their future, there are
other questions involved which possess
profound interest for the philosopher |
We know that the earth is a magnet,
but as yet no one is able to say what |
makes it so. The fundamental secret of |
terrestrial magnetism has not been |
solved. Then, too. there are various |
changes in direction which mark the |
behavior of the needle that remain TO |
ce explained. What influence is it that |
makes the needle swing to and fro to a |
extent every day? Why is it |
hat the diurnal swing is greater in
7ears of sun spct abundance than at the |
minimum stage Of solar activity: Why |
10 the indications of the needle differ
n summer from those of winter? What |