The daily sentinel., 1910-05-03

"If the earth should pass through
the tail of Halley's comet, as astron-
omers expect it will on the 18th of
May next. an opportunity of kind
that has not previously occurred in
the history of the weather bureau
will be offered for the study of cer-
tain phenomena. Owing to the posi-
/ tion of the moon on the given dates,
/ II is probable that he most satisfac-
| tory night observations will be OBJ
/ tained during the last two or three
hours before daylight. Please OBJ
serve as many of the following phe-
nomena as you understand and feel
capable of handling:
"1. Auroral Displays.-Auroras
serve as indicators of the electrical
state of the outer atmosphere; and,
as this state possibly may be affected
/ by the tail of the comet as we pass
through it,o auroras should be
watched for at that time. The loca-
ton. color, shape, extent and other
/ features, as well as the times OF ap-
pearanCe. changes and disappearance,
should all be carefully noted.
"2. Meteoric Trails.-The num-
ber, times of appearance, lengths OF
duration, and directions and lengths
of visible paths of meteors should be
noted on all three nights, but espe-
cially on the night of the 18th.
! "3. Bishops Ring-This curious
dust halo was seen around the sun
after the eruptions both of Krakatoa
and Mont Pele, and conceivably may
also follow the passage of the earth
through the tail of comet 1t, there
| fore, should be carefully looked for
on the days specified. and, occasion
ally, for some days thereafter. AS
the light of this ring is rather faint,
observations of it are best made when
the sun is hidden behind some steeple
or other Opaque object.
"A. Color OF the Sun and Sky
Both the general color of the sky and
the color of the sun depend on the
dust and other contents of the at
mosphere. and should be carefully
noted on the given dates.
20. Twilight Phenomena.-Twi-
light colors. their distribution and
order of changes depend largely on
the dust in the atmosphere, and, con-
sequently, these are phenomena that
need to be observed on the days in
dicated
"6. Luminous Clouds.-Neither
the material of these clouds nor the
cause of their light is definitely
known. They seem to belong to the
very high atmosphere, and therefore
should be looked for at night in con-
nection with our transit across the
comets tail. These clouds are cir
rus-like in appearance. but may be
distinguished from the true cirrus
by the fact that they are brighter
than the background of the clear
nocturnal sky, During the fore part
of the night they are seen above the
northwestern horizon.
recently done at the Lick and at the
Mount Wilson observatores, it seems
probable that the zodiacal light is
Y. Zodiacal Light.-From work
caused by the reflection of solar light
from dust in and near the plane of
the ecliptic. If so, then a change
might be expected in it at the time
oil the comets near approach to the
earth, and therefore the extent and
orilliancy and other features of the
zodiacal light as they appear at that
time should be carefully noted.
., Gegenschein Counter Glow.
But little is known of the cause of
this faint glow seen in the ecliptic
at a point directly opposite to the
sun, or along the shadow of the earth
presumably it has the same origin as
the zodiacal light, and consequently
may be modified during the transit of
the earth across the tail of a comet
AT any rate, it should be observed on
the nights mentioned, and its brill
fancy at these times compared with
that on nights when there certainly
is no cometary disturbance. To To-
cate the gegenschein at any hour of
the night, look in the direction where
the sun was ~ hours previously.
" General Phenomena.-Solar
ana lunar halos and coronas, and ali
other appearances that may seem un-