I, too, have always believed that the zodiacal light
rotated; but I assumed (contrary to Poisson's opinion, which you have
communicated to me) that it completely extended to the Sun, with
considerably augmenting brightness. The light circle which, in total solar
eclipses, is seen surrounding the darkened Sun, I have regarded as the
brightest portion of the zodiacal light. I have convinced my self that this
light is very different in different years, often for several successive
years being very bright and diffused, while in othr years it is scarcely
perceptible. I tyhink that I find the first trace of an allusion to the
zodiacal light in a letter from Rothmann to Tycho, in which he mentions that
in the spring he has observed the twilight did not close until the sun was
24??degrees below the horizon. Rothmann must certainly have confounded the
disappearance of the setting zodiacal light in the vapors of the western
horizon with the actual cessation of twilight. I have failed to observe the
pulsations of the light, probably on account of the faintness with which it
appears in these countries. You are, however, certainly right in ascribing
those rapid variations in the light of the heavenly bodies, which you have
perceived in tropical climates, to our own atmosphere, and especially to its
higher regions.
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