The Washington times., 1922-06-04

In the early morning OF Sep
tenber 81, by Greenwich time. the
sun will be totally eclipsed for
rather more than three hours
along a belt Of the earth about
100 miles wide and stretching
from east coast Of Africa, In
somaliland, to Q point in the
Pacific ocean some $500 miles
east Of Australia. With the ex.
ception Of a small region Of
somaliiand and the continent Of
Australia, the only dry land from
which the total phase will be Wis
ible consists Of few small islands
In the Indian ocean. and at no place
will totaiity last as Ion gas SIX
minutes, = but in the short time
available astronomers who have
made preparations for viewing the
phenomenon from selecIed islands
and stations in Australia are hop
ing to make observations and tnkA
photographs OF tho ecllpsed sun
which will materially hep forward
the science Of solar physics.
Method Of Test.
The most important Of the va.
rious expeditions projected IL that
which has gone out from the
Greenwich Observatory to Christ
mas island, which lies In the In.
dian ocean more than a thousand
miles northwest Of Australia: for
this party, which IL IN charge OF
H. Spencer Jones, the astronomer
royals chief assistant. viii take
photographs OF the stars near the
sun when totally eclipsed Ly which
to submit to a test Einstein'S pre-.
diction regarding starlight passing
near the sun. The amount by
which the light rays should be
disturbed varies with the distance
from the suns center, and the
maximum displacement That Il II
possible to observe. assuming Il
takes place, Ia less than a second
of arc, which is the apparent
diameter Of a rs cent piece seen
from q distance of AIS miles.
But where astronomical measure
ments are concerned this 10 quite
a large defleectiop.
As Christmas Island Is not cen.
trally situated in the belt along
which the approximately circular
shadow OF the moon will pass
during the total phase. but some
thirty miles north Of the central
line, the duration of totality will
be only three and three.fourths
minutes. but the eclipse will
happen there at local midday, and
with everything prepared before.
hand several photographs will
be taken II the weather Is favor
able. Subsequently these photo
graphs will be carefully measured
by the refined methods available
al Greenwich, and the positions
of the stars shown on them com.
pared with those of the same
stars on plates already taken at
Greenwich when the sun was in
another part Of the sky and the
light OF the stars therefore un'
affected by the solar Bravita-
uonal field.
Second Attempt.
This will be the second occasion
on which Einstein's prediction has
been tested during a total eclipse.
The previous occasion was In May
1919, when. owing to the sudden
termination Of the war providing
an unexpected opportunity. the
Greenwich expeditions, which went
to West Africa and South America
for the purpose, had to use instru.
ments the reliability OF which was
criticised. and though the photo
graphs then obtained showed stell-
ar displacements IN close agree.
ment with the predicted amount,
they were not generally accepted
by scientists as absolute corrobora.
ton Of Einst tein's theory.
But on this occasion the most
elaborate preparation have been
made to eliminatae, so far as ID
humanity possible. every source OF
error. BY permission Of the ad'
miralty the l3-inch astrographic
telescope at Greenwich Conserva.
tory was some months ago dis.
mantled and sent to Christmas Is.
land, where It has been specially