The Saint Paul globe. (St. Paul, Minn.) 1896-1905, 1898-08-08

tn the study of the spectrum of the
layer of gases lying Immediately above
the dazzling photosphere, and known
as the flash spectrum
1t may be well to explain, for the
benefit of those who are unfamiliar
Which this spectrum Is revealed dur
ing an eclipse. Outside the visible sur
face of the sun, and covering the en-
tire sphere pretty uniformly there ex-
lists stratum of gas of considerable
depth and comparatively simple COM
position. known as the Chrome
sphere" It's spectrum Of bright lines
indicates the presence of the three ele-
ments, calcium, hydrogen and helium.
This layer and the prominences arising
from it may be seen at all times by the
aid Of powerful spectHscopes, but the
base Of the chromOsphere is not access
sible to ordinary spectroScOpic observa-
ton on account of the perpetual I'M
steadiness Of the telescope image of
the sun. and the very intense atmos-
pheric illumination so near to the suns
edge.
Now, during the progress of a total
eclipse, the moon, advancing from the
west gradually covers the protosphere
until only g thin crescent remains on
the east side, and this rapidly mar
rows down and finally vanishes alto
gether; when this occurss. however,
the cromosphere lying outside still re-
mains uneclipsed on the east limb, and
even the very lowest strata are uncov-
cred near the point where the last
streak Of photosphere disappeared.
EXPECTED PHENOMENA.
1t Is just here that the most interest
ing and beautiful spectral phenomena
are revealed; bright lines flash out in
hundreds-there seems literally to be a
shower of bright lines all along the
spectrum the moment the photospheric
light is withdrawn-but it is only mo-
mentary; the steadily advancing moon
almost Immediately occults the lowest
gaseous strata, and only the ordinary
chromospheric spectrum remains.
This beautiful phenomenon can
therefore only be seen or photographed
at the moments of disappearance or
temperance of the philosophers at the
beginning or the end Of the total phase
respectively. Under the average con-
ditions of an eclipse. perhaps not more
than two seconds are available just as
totality comes on In which the flash
spectrum may he photographed in it's
full splendor; and if the observer Is
discerning enough to know exactly
when the sun Is going to burst out
again at the end Of totality, he will
have another two seconds in which to
expose a second plate.
The photographs which accompany
this article were obtained at the re-
cent eclipse with a small instrument,
which I constructed in 1896, for the
eclipse of that year.
Before proceeding to describe in de-
tail the results obtained. will give a
brief description Of the arrangements
I made for this work at the camp Of
the British Astronomical association
stationed at Talni.
My plan Of work was first to obtain
a series of ten photographs with the
prismatic camera during totality, and
Including, If possible, the flash spec
trurn at both second and third CON
facts; secondly. to photograph the flash
spectrum on a larger scale with large
slitless spectrograph attached to six
inch telescope; and, thirdly, to expose
a single plate to the spectrum Of the
corona during the whole time Of total
ity by means Of a slit spectPegraph con-
tanning quartz prisms
TELESCOPE AND HELIOSTAT.
Besides these three Photographic in
struments had available a four-inch
polar heltoatat. and q three and 4 quar-