Attempt to apply instrumental measurement to the Zodiacal Light

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                                Taking all the above facts into consideration, we are 
perhaps entitles to conclude on pretty good foundation, that the 
Zodiacal light is an extremely oblate, lenticular revolving body, nearly 
in the plane of the Sun's equator rather excentrically situated, 
of so vast a size as <s>to<\s> nearly to fill the whole orbit of the earth, & 
sometimes actually to reach it. But whether it does actually 
at this present  time correspond exactly with the Sun's equator, 
and if it always has done so and always will; whether the mani=
=fest changes in the intrinsic brightness, and the form and 
size of the light that have been obtained, be due merely to 
a rotation of the excentric or oval body, or to a real periodical 
increase of the intensity of its emanations or an enlargement of 
its dimensions, - are matters still to be determined by observation. 
The physical constitution of the Zodiacal light 
seems also well worthy of being inquired into. The most pro=
=bable supposition is that, which makes it consist of innumerable 
small planetary particles revolving about the sun, and shining by 
reflected, or not impossibly, by direct light. Not impossibly, because 
while, - on the one hand the occasional crossing of the earth's orbit 
by the extreme portions of the Zodiacal light, has been by many 
held to be the origin of the shooting stars; and many of these 
have been found to be at the time of their incandescence several 
hundred miles above the earth's surface, and thus, far above 
the limits of the atmosphere, whose friction might have imparted 
such a degree of heat to a body at a lower altitude, moving 
with a velocity of 1000 miles per minute: - on the other hand, 
M. Mathieson has recently made some most interesting ex=
=periments, in which the thermomultiplier showed evident 
indications of <u>radiant<\u> and therefore <u>direct heat<\u>, proceeding from 
the Zodiacal Light. (Comptes Rendues, T. XVI, p. 687. Ap. 143.) 
But in its resent stage the subject can only be pro=
=fitably and successfully prosecuted in other climates, in 
countries where the twilight is shorter, where the ecliptic makes, 
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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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