Evening star. [volume] (Washington, D.C.) 1854-1972, 1907-03-09

the total of the earth's magnetism in the
region of the observatory. All of the other
magnetic observatories of the world Will
probably report similar phenomena AT the
time of the last great sun spot visitation
October, 1903-the writer obtained similar
report from the coast survey-that It's Chel-
tenham station had observed an unusually
severe magnetic storm lasting over four
days.
Great Sun Spot Camera.
This big solar camera, daily employed in
the governments search for sun spots,
stretches out, north and south, over the
lawn of the Naval Observatory Park, and
covers about fifty feet. over all. Its box
is a snug little cottage-more pretentious
than many an abode of man. Inside there
is dark room where, upon a pedestal.
stands the holder, daily renewed with the
Photographic plate which reproduces the
image of the sun. This image. entering
five-foot lens at the north end of the struct-
ure. is projected through a long shingled
shed which has the function Of the bellows
of our portable cameras. The lens receives
the suns image from a movable reflector
of unsilvered glass mounted upon pier Of
masonry and directed toward the sun.
BY courtesy of Rear Admiral Asa Walker,
superintendent of the naval observatory,
the writer is enabled to reproduce with this
article a photograph made directly from Mr..
Peters best negative of the sun spot now
so much in the limelight. Examination Of
the negative shows that the great spot is
really a great cluster of separate mottlings.
This cluster, taken a whole, measures
about 10000 miles long by about $4,000
miles wide. In other words, a vast cross
made by placing six earths side by side in
one direction and sixteen earths end to end
in the other direction would fit snugly into
this space.
But We were speaking. too, about the
magnetic phenomena which accompany
these eruptions upon the suns face. In the
past few years the government has erected
magnetic observatores upon Mt. Weather,
Va. Vieques Island, P. R.; Oahu Island, Ha-
wall; at Siika, Alaska, and Chetenham
Nd. That at Mt. Weather is an adjunct
of the new research observatory of the
United States weather bureau lately erect
ed upon that crest of the Blue Ridge noun
tains while the others named are maintain
ed by the coast and geodetic survey.
Measuring Magnetic Storms
In these observatories delicate instru-
ments are constantly making record of that
f1uctuating, pulsating, magnetic climate
which bathes earth and which is distinct
from the weather of the meteorologist.
OF these instruments the magnet is the SEN
%itive hand as it is In the compass In one
the magnet. delicately poised to move hori-
zontally-like the needle of the mariner
measures the magnetic variation from the
true north and south. In another the mag
net poised to seesaw upon a vertical plane
measures changes in the magnetic intensity
of the earth. Each of these magnet bars.
however balanced carries minute search
light, which reflects a sharp beam upon a
moving sheet of Photographic paper AS
these little spots of light travel across the
paper they leave black paths behind them
Since the paper is renewed at given hour
every day the record of the earth's
magnetic climate is to be kept as perpet-
ually as were the fires in the Temple of
Vest. Where these paths appear straight
upon the paper the earth's magnetism has
been uniform. but where they appear jag
ged and zigzag there is evidence of mag
netic storm-not a thunder storm or .'elec-
trio storm. but one of those silent vista
tions of earth currents which disturb the
mariners and surveyors compasses and
frequently cause trouble on telegraph lines
So delicate are these recording instru-