Attempt to apply instrumental measurement to the Zodiacal Light

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                                way, increased transversely from either side to the central longitu-
=dinal axis & from the apex downwards, until overpowered by the haze 
on the horizon. 
Now, two circumstances worthy of note were pointed 
out by this might's observation, 1<sup>stly<\sup> that persons did not always 
know exactly where to look for the zodiacal light, nor what sort 
 of object to expect; and 2<sup>ndly<\sup> that the theory was greatly in 
error, & for an astronomical matter, grievously wrong. Both 
classes of mistakes may have been brought about in no small 
degree by the injudicious mixing up of erroneous theoretical & 
speculative views, with the simple nomenclature of the phenome=
All that can be asserted from a single observation, & 
perhaps indeed from all the observations that have been made, 
up to the present time, is that a light  appears in the Zodiac; 
and if it be called "the Zodiacal light", no idea except the 
visible fact itself is included. But to  call it the "Sun's atmos=
=phere", is taking for granted a supposed fact which has never 
been proved, and imagining the body to obey peculiar laws, to 
which it may not really be subject. Moreover, as in the case of 
a phenomenon which is so extremely faint as scarcely to be 
seen at all, - a person may too easily persuade himself that 
he sees it as he <u>ought<\u> to see it, - so there seemed to be much 
necessity for making further observations, which though they 
might prove after all to be not entirely free from errors of 
judgement & idea, yet would probably not be affected in the 
same way as those of other observers. 
The circumstances in which I was placed were very favou=
=rable so far as the clearness of the sky, the purity of the atmosphere, 
and the advantage of geographical position were concerned; but 
being engaged in the active duties of a trigonometrical survey, 
sometimes on the top of high mountains, & sometimes in the 
plains below, the different character of the stations exercised 
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Manuscript details

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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