LOW-SUN PHENOMENA IN LUZON 
II. ZENITH OBSERVATIONS OF DAWN, BAGUIO, 1920 
By Wiiuarp J. FISHER 
Assistant Professor of Physics, University of the Philippines 
In a previous paper* I have made an attempt to determine a 
lower limit to the extent of the atmosphere by noting at a known 
geographical position the time when the zenithal region becomes 
perceptibly blue. It was there mentioned that this blue colora- 
tion is preceded by a pale light spreading upward from the 
lower parts of the Zodiacal Light, and that the artificial illumina- 
tion of the lower hazy air by the light of Manila prevents there 
any consistent observations of this “pale dawn.” 
April 17-18, 1919, from the summit of Mount Santo Tomas, 
elevation 2,258 meters, near Baguio, Benguet, I observed that 
faint stars were visible at very small angular altitudes; and that 
the haze of the lower air extended only to a height of about 
1,500 meters, because a mountain 1,590 meters high projected 
slightly above the haze; so it was evident that from such a 
station in the Mountain Province the zenith passage of the 
pale dawn might be observed with fair accuracy. During a visit 
to Baguio, April 10 to May 2, 1920, made for this and related 
purposes, I was unfortunately prevented from visiting Santo 
Tomas; but from a station on the Outlook Drive, called Outlook 
Point on Bach’s Map of the City of Baguio, I made six morning 
observations of this phenomenon—nearly all that it was possible 
to make between the new moon of April 19 and the full moon of 
May 3, for strato-cumulus and cirro-stratus clouds spoiled some 
mornings. 
In the previous paper it was shown that the presence of the 
Zodiacal Light near the zenith was a hindrance to the prompt 
perception of the blue color at the zenith, while the same location 
of the Milky Way had less influence. But I found that the 
brilliancy of the Galaxy in the zenith sky of Outlook Point quite 
outshone the pale silvery light whose appearance I was to ob- 
? Fisher, W. J., Philip. Journ. Sci. (1920) 151. 
: 487 
