Attempt to apply instrumental measurement to the Zodiacal Light

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                                favourable circumstances". 
"Those who have dwelt long", says he, "in the zone of 
Palms, must retain a pleasing remembrance of the mild 
radiance of this phenomenon, which, rising pyramidally, il=
=lumines a portion of the unvarying length of the tropical 
nights. I have seen it occasionally shine with a brightness 
greater than that of the Milky Way near the constellation of 
Sagittarius; and this not only in the dry and highly rarified atmos=
=phere of the summits of the Andes, at elevations of thirteen 
to fifteen thousand feet, but also in the boundless grassy plains 
or <u>llanos<\u> of Venezuela, and on the sea coast under the ever clear 
sky of Cumana. The phenomenon is one of peculiar beauty 
when a small fleecy cloud is projected against the zodiacal light, 
and detaches itself picturesquely from the illuminated back-
ground. A passage in my journal during a voyage from 
Lima to the West Coast of Mexico, notices such a picture. 'For 
the last three or four nights (between 10[degree] & 14[degree] of North latitude) 
the Zodiacal light has appeared with a magnificence which 
I have neverbefore seen. Judging also from the brightness of 
the stars and nebulae, the transparency of the atmosphere 
in this part of the Pacific must be extremely great. From the 
14th to the 19th of March, during a very regular interval of 
three quarters of an hour after the disk of the sun had sunk 
below the horizon, no trace of the zodiacal light could be 
seen, although the night was perfectly dark; but an hour 
after sunset it became suddenly visible, extending in great 
beauty and brightness between Aldebaran and the Pleiades, and, 
on the 18th of March attaining an altitude of 39[degree], 5'. Long 
narrow clouds, scattered over the lovely azure of the sky, appeared 
low down on the horizon, as if in front of a golden curtain, 
while bright varied tints played from time to time on the 
higher clouds: it seemed a second sunset. Towards that 
<s>part<\s> side of the heavens the light diffused appeared almost 
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Manuscript details

Charles Piazzi Smyth
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Cite as

Attempt to apply instrumental measurement to the Zodiacal Light , 1840. From The Royal Society, AP/30/18



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