The Saint Paul globe. (St. Paul, Minn.) 1896-1905, 1898-08-08
ing the form of the little crescent of
pbotosphere remaining uncovered.
TIE RPTCuT JJNES


The band of continuous spectrum in
which these dark lines appeared was
seen to be rapidly narrowing, but, IA
stead Of thinning down to a single
thread, the roughness of the moons
edge caused 1t to suddenly break up
into number Of strips With dark
spaces between. and at this instant the
bright lines flashed out in hundreds
between and across the streaks of con-
ttnuous spectrum. I was astonished at
the SuddennesS Of the reversal of dark
lines to bright, and at the brilliancy
and extreme sharpness of the lines;
many Of them extended for thirty de-
grees or more round the limb of the
moon, but interrupted here and there
by the projecting lunar mountains
Without waiting for further develop
ments 1 Immediately exposed the pris-
matte camera and the large specto-
graph, in hopes that the Photographic
plate would be equal to the occasion
and duly record this wonderful display.
In the resulting photograph certainly
not all of the finer lines are depicted
which [ could see reversed in the part
OF the spectrum 1 was observing. But
in the ultraviolet, where the definl-
ton is best, an extraordinary wealth of
nne lines is shown.
The number Of photographs secured
altogether was thirteen; one with the
slit spectograph, two with the large
spectograph and ten with the prismatic
camera.
The single photograph obtained with
the first named failed, the direct sun
light and halation nearly celebrating
the faint coronal spectrum.
The large spectograph yielded two
negatives Four of the series give the
spectrum of the cups just before and
the Fraunhofer dark line spectrum
bordered with bright lines, and in one
all the dark lines in the ultra violet
end in a short, bright line.
HYDROGEN RADIATIONS.
Of the remaining plates, one reveals
a curious feature in the prominence
spectrum. In the ultraviolet are seen
a succession of little dots due to the
hydrogen radiations, and at the point
where these terminate the spectrum
abruptly changes its character and be-
comes a continuous one, a delicate
line running from the last dot to the
end of the plate.
The long exposures made near mid
totally show the distribution of Co
rOn1um In the corona. The well known
radiation Of this gas is, In these, shown
to correspond more or less with the
general structure of the corona; but it
Is very much brighter on the east side
than on the west, where it is hard to
trace it all.
Another point which is we'll shown Is
that, If we except the ordinary chro-
mosphere lines Chose of calcium, n.y.
drogen and helium), all the fainter lines
due to the flash spectrum proper are
Of the same length and form, a well
defined length of even width running
from end to end of the spectrum. This
shows that the low lying gashes at the
base of the chromosphere form a we'll
defined layer pretty definitely bounded,
and not failing by insensible gTada-
tons into the higher portions of the
chromosphere.
An estimate based on the width Of
this band of bright lines gives for the
depth of the layer about one and a
half seconds of arc-or say TOO miles
the total depth Of the chromosphere
itself being some eight seconds of arc.
or 1900 miles.