16, 2 Fisher: Low-Sun Phenomena in Luzon 153 
minous, either by emission or by the reflection (or scattering) 
of sunlight. 
Near the plane of the ecliptic this brightness of the sky is 
concentrated in the Zodiacal Light. Under favorable circum- 
stances this is seen clear across the heavens as an arch or band 
of light; at Manila and Batangas, both near sea level, I have 
seen it as far as the zenith with the sun an hour below the 
horizon. The Gegenschein is a faintly brighter spot in the 
Zodiacal Light, 180° away from the sun; I doubt if it is ever 
to be seen against the artificially bright sky of Manila. The 
Zodiacal Light widens toward the sun; it completely surrounds 
this, as is known by observations of Simon Newcomb and others, 
looking northward from suitable stations in the northern hemis- 
Phere, at about midnight near the summer solstice. 
As the hour of dawn at Manila approaches, the Zodiacal Light 
broadens and brightens in its lower parts, so that stratus clouds 
Show distinctly as dark bands across it. Then a pale light 
Spreads upward from the east; in Manila this does not seem 
to start even at the physical horizon of mountains and clouds, 
but higher up, where atmospheric absorption exerts a less 
weakening effect on the Zodiacal Light. Whether this pale light 
is distinguishable from the Zodiacal Light or has a definitely 
terrestrial origin, I think cannot be settled at Manila; I watched 
carefully at Batangas, after sunset, February 22, 1919, but could 
hot decide; I have had no other good opportunity. Some ob- 
Servers say the transition is continuous. 
As this “pale dawn” rises toward the zenith the lower eastern 
sky begins to be brighter and even ruddy, and above that bluish. 
he pale dawn passes the zenith, and the blue dawn follows it 
ver the heavens. Then there pass upward and sidewise the 
familiar and often-described colored arches and bands of morning 
twilight,’ frequently with the bright streaks and blue bands 
radiating from the sun’s position, known as crepuscular rays 
and shadows, followed by the appearance of the sun itself, and 
the daylight changes of the atmosphere. 
Since the days of the Arabian Alhazen attempts have been 
made by various observers to determine a lower limit for the 
height of the atmosphere by observing the time when the pale 
light of twilight first appears or last disappears at the horizon. 
d "Mo. Weath, Rev. 44 (1916) 614 and following pages, contains full 
ns of these phenomena, original, translated, or abstracted; so also 
© the numerous books on meteorology. 
