Attempt to apply instrumental measurement to the Zodiacal Light

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                                twilight has disappeared; but as the other end rises in the morning 
at that season necessarily at an angle 30 degrees less than that of 
the equator, the apex in its slanting position hardly rises above 
the mists of the horizon before the twilight illumines the sky. 
In the month of September matters are just reversed,* and the 
Zodiacal light rising in the morning at a greater angle than 
the equator is then well seen, but is not at all visible in the 
evening, when, from the slanting position of the body, the apex 
sets very soon after the Sun. And in these two short appropriate 
seasons, so many of the nights may be rendered untoward by 
clouds, strong moonlight, and other causes, that an opportunity 
of seeing the Zodiacal light may even then rarely be enjoyed. 
Similarly in the Southern Hemisphere in 56[degree] S. Lat. 
supposing also, as before, that the Zodiacal light stretches out 
equally from the Sun on every side in the plane of his equator, 
the two most favourable opportunities in the course of the year 
for viewing the body would be, in the evening in the month of 
September, and in the morning in the month of March. And 
that this would usually be the case, the observations made in 
Lat. 33 S. sufficiently attest. 
In order to give a clearer <s>description<\s> conception of what may be 
expected to be seen, than can be conveyed in words alone, I have 
subjoined a number of drawings both of what the Zodiacal light 
is and what it is not; the latter being the great comet of 1668, & 
1843, mistaken on both occasions for the more permanent mem=
=ber of the system. The object in the construction of the drawings 
has been, in as far as it was possible to be compassed by the small 
skill of the author, to give so complete a reproduction of all 
the attendant phenomena and circumstances of climate or 
country, as to enable any one who looks at them to form a 
tolerable idea whether any of the accompanying conditions, under 
which the original view was obtained, seem likely to produce 
an erroneous judgement in the spectator of the exact form 
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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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