Sodium in the Upper Atmosphere.

Spectroscopic and interferometer observations show conclusively that the bright yellow radiation of the night sky coincides with the two D lines and that sodium atoms are always present in the upper atmosphere. At twilight the yellow radiation is in- creased, like the red line X 6300 of [0 ii. The writers are examining the altitude of the luminescent layer and the origin of atmospheric sodium; they believe that the sodium comes from meteorites