, 1899-03-01
. SERIOUS PROBLEM.
THE COMPASS AND THE GROWING
USE OF ELECTRICITY.

Although the invention and introduce
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 A. w. Rucker at a recent
the Advancement of Science.
In various parts of the 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. 1t was long & discov-
cred not only that the compass does not
aim directly at the north pole, but that
the amount OF variation in its indica-
tons 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
hignest importance to the surveyor and
mariner-it is requisite hat careful OBJ
SeryatiOns be 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 a,I in Toronto.
The Interference of tho 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 other metallic objects about
their persons before entering the apart
ment. The magnets, generally oars OF
steel not over Six inches long, are poised
above a scale that is graduated to the
most minute fractions, and a telescope,
on a adjacent pillar, is used to read
the fluctuations, which are too small to
be discernible by the unassisted aye. A
tiny mirror, Os big as a dime, catches q
beam of light more slender than the
lead in a pencil and reflects it away 20
a sheet of slowly moving Photographic
paper, Oh which a permanent record is
made. The arrangement of the apparatus
is such that the movement Of the mag
net is magnitied 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
in which it acts. And so sensitive are
they that their readings are apt to he
interfered with by exceedingly trivial
causes, 1t is customary for the superin.
tendent to inscribe OH the scroll "Visit-
ors admitted, whenever such a breach
of the regulations is permitted, so that
if any abnormal fluctuation is detected
in the motion of the magnets a suspicion
Of its meaning will he excited in the
mind of the scientist who afterward ex-
amines the Photographic trace.
In spite of the delicaoy of the appa.
ratus. it may seem surprising to the lay
mind that the passage of trolley cur
rents at a 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 in terrestrial magnetism
from those which are caused by the
trolley. Professor Rucker said a few
days ago: From all parts of the world
we hear of observatories ruined or
threatened by the invasion OF the cleo
trical engineer. Toronto and Washing
ton have already succumbed, Potsdam,
Pare St. Maur, Greenwich and Kew are
besieged, and the issue largely depends
| upon whether these great national OBJ
servatories can or cannot make good
their Defense"
Although the practical service to
mankind which is rendered by institu-
lions of this class is alone sufficient to
justify their maintenance and to war
rdht-.larm 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 NJ 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
be explained What influence is it that
makes the needle swing to and fro to a
microscopic extent every day? Why is it
hat the diurnal swing is greater in
years of sur spot abundance than at the
minimum stage of solar activity! Why
do the indications of the needle differ
in summer from those of winter? What
Is the key to the mystery of the long
period movement that makes it neces-
sary to reChart the situation? What
causes the c%unvulsive behavior of the
magnets for n few hours or days when
there Is a great outbreak of sun spots?
And Is there any relation between the
weather and the fluctuations in the
earths magnetism! There are theories
Oh these subjects, but no generally ac.
tented hnpt u,,I thn ,r,, vr,s,~i