Attempt to apply instrumental measurement to the Zodiacal Light

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                                N,sup>o<\sup> 610 Received 13 April 1848 S.H.C. Withdrawn 2<sup>nd<\sup> Nov<sup>r<\sup> Archives S.H.C. 
Attempt to apply Instrumental Measurements 
to the Zodiacal Light. By Professor Charles Piazzi Smyth, 
F.R.S.E. & F.R.A.S. Astronomer-Royal for Scotland. Communicated by Captain W.H. Smyth, 
F.R.S. &c 
When preparing to make a night-journey over one of 
the plains of South Africa, in the month of June 1843, a friend 
called my attention to the peculiar appearance of the sky in the 
west, as offering a very decided proof, agreeably with theory that 
there was no "Solar Atmosphere" to be seen at that season of 
the year. 
On looking in the direction mentioned, the last portion 
of the twilight was just visible, & forming a peculiarly level 
line above the place where the sun had set, for an extent 
in azimuth of perhaps 40 degrees, and at a height of about 
5[degree]. all the gorgeous colours which had attended the setting 
of the sun, had long since vanished, and there only remained 
sufficient light within the flattened arc described, to make 
the space, included between it and the horizon, appear <u>light<\s> 
blue, while all the rest of the sky had attained a deeper colour, 
nay, almost black, & was thickly spangled with small as 
well as large stars. 
There most decidedly was not any symptom 
then of the so-called "way of the twilight shooting upward." 
But as soon as the last illuminated portion of the Wes-
tern sky had set, the last phenomenon, i.e, the Zodiacal light, 
appeared in an unmistakeable manner, rising up in the 
ecliptic to a height of 50 degrees, with a breadth of perhaps 12 
at the horizon; & forming, with the vast extent of its illumi-
=nated surface, and the regularity of its contour, - one of the 
most remarkable objects in the starry sky. The form was that 
usually described, viz, a wedge pointing upwards with curved 
sides, of excessively indefinite outline; but still, as far as could 
be judged, free from any irregularities: the light, which was 
more delicate and transparent than that of the milky 
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Charles Piazzi Smyth
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Attempt to apply instrumental measurement to the Zodiacal Light , 1840. From The Royal Society, AP/30/18



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