The Dickinson press., 1899-01-28

s%@TgT~
A SERIOUS, PROBLEM.
THE COMPASS AND THE, eRowlNo
USE OF ELECTRICITY
;f3a} 2lTIx4 -s+@f1 1aG& 2.
A Danger. That the Magnetic Needle
May Be Rendered& Practically USE
less to the Mariner and the Sur
veyor-A Curious Discovery.
Althoughsthe invention and introduce
tion 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
wal laid on one Of these drawbacks to
electric traction in the address delivered
by Professor A.sW"Ruoker at d recent
meeting Of the British Association For
the ADVANCEMENT Of Science. 4 7
>InFvarious partsDfthe world observa-
tories have been established for the pur-
pose of keeping track of the changes in
the direction in which the magnetic
needle points. It 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 indica-
tions from true north undergoes slow
alterations. Hence 1t 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 thsataoafeful Oh.
servations be- madaaoontintously 1t 70
number Of widely separated points.
Two Of the most famous and hitherto
useful institutions of thisolass are stu
atddlih Washington, in 1.-THE grounds Of
sthe 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 go much with the behavior Of
the instruments Of both places that the
records now obtained are practically
worthless. And the experts are greatly
puzzled blythe, problem Of es9apinghom
this senAtioush hterfnptie1sSof their
yes;, 49, 49,, ~ H., !
the magnets in such an observatory are
intended to investigate that they a be
perceived only when the apparatus is
most scrupulously guarded, Thereon
in which they ate .@oratedSAiss ghder-
ground. Vidtoesiafanstsf adfnitsedex
oept under unusual circumstances and
are required to deposit their jaokknives,
keys and all other metallic objects about
their persons before entering the apart
ment. The magnets, generally bars Of
steel not over Elk inches long, are poised
above a scale that is graduated to the
most minute fractions, and a telescope,
on an adjacent pillar, is used to read
the fuotnations, which are too small to
be discernible by the unassisted eye. A
tiny mirror, as big as a dime, catches a
beam Of light more slender than the
lead in a pencil and reflects 1t away to
a sheet of slowly moving Photographic
paper, on which a permanent record is
made. The arrangement Of the apparatus
is such that the movement Of the mag
net is magnifed many times in the rec
ord, in order to render the changes per-
ceptible.
There are three sets Of instruments
on duty in such an observatory. One
swings horizontally, like a mariners
compass. Another dips up and down.
A third is designed to measure the In.
tensity of the earth's magnetism, which
is a separate thing from the direction
lin which it acts. And so sensitive art
they that their readings are apt to BIZ
interfered with by exceedingly trivia.
causes. .Itis customary for the ,superin
tendent .%tolinscdBe On the scroll Visit
ors admitted" whenever. such a breach
Of <theregulations IL permittea, 30 tha'
If any abnormal huctuation Is detected
in the motion of the magnets a suspicion
Of It's Sm1sanihg. will ts excited Id th,
mind Of the scientist who afterward ex
aminesfthe, Photographic trace. gyr L
In spite II the delloacy Of the appa
ratus. it may seem surprising to the la!
mind that the passage Of trolley cur
rents at a distance Of many rods from
the observatory should be able to affec
the instruments within. But they do
and it is impossible to separate in tn
record the variations produced by genu
inc changes in terrestrial magnetism
from those which are caused by tn
trolley. Professor Rucker said a few
days ago: "Ffom all parts Of the worl,
vi hear Of o~bservatories ruined o
threatened by the invasion Of the cleo
trioal engineer. Toronto and Washing
ton have already sucoumbed, Potsdam
Pare st. Maur, Greenwich and Kew ar
besieged, and the tissue largely depend
upon whether these great national oh
servatories can o. cannot make goo
their Defense"
Although the practical service {
mankind which Ia rendered by institu
tions of this class is alone sufficient
Justify their maintenance and to wa,
rant alarm ~ to their future, there al
other questions involved which possei
profound interest for the philosopher
We know that the earth is a magne
but as yet no one is able to say VIII,
makes 1t 90. The fundAnental secret
tefresrial magnetism has not bee
solved. Then, too, there are yario,
changes In Ab1csiha taktth mark IA
behavior OF the needle that remain
IS axplainsd. What influence is 1t tn
akes the needle swing TO and fro to
sS micro Observation-Disclosures 4ayla Why II