xlviii Appendix. 
cannot do better than quote what he says on this subject [Extract read ; 
Keith Johnston’s “ Atlas of Astronomy,” page 5.] I have brought with me 
the illustration referred to by Mr. Hind which, judging from my own observa- 
tion and from the accounts of others, conveys a fair representation of the 
phenomenon. 
With regard to the time of the year during which the Zodiacal Light is 
* visible in England, the record of the Rev. T. W. Webb in “Nature,” 8th 
February, 1872 (vol. v., p. 285), of the latest observations there, of which I 
have seen an acount, corroborates what Mr. Hind says on the subject. 
Of the only observation of the Zodiacal Light which I have had the 
opportunity of making in this hemisphere, I can only speak from memory. 
It was during the winter months, and the apex of the cone of light, which 
was on that occasion defined with more than usual clearness, was near one of 
the brighter stars in the constellation Leo. The sun was at the time far below 
the horizon, and the distance of the apex from the horizon was fully 40°. 
A reference to Mr. Skey’s diagram will show that if the figure he has given 
as an approximation to that of the Zodiacal Light is to be taken as an 
essential detail of his hypothesis, this observation, and indeed all observations 
during our winter months, decidedly invalidate it. As I have already said, 
this particular detail does not appear to be essential to the theory, although it 
renders it desirable that the manner in which it has been expressed should be 
revised. The general furm of the envelope from which we derive the Zodiacal 
Light may be somewhat as Mr. Skey has supposed, but it-is necessary to 
admit of a very considerable extension in all directions from the sun in and 
near the plane of his equator, in order to account for its visibility throughout 
the year. 
Various hypotheses as to the constitution of this solar envelope have been 
put forward. Sir John Herschel speaks of it in his “ Outlines of Astronomy,” 
paragraphs 897 and 898. Becquerel, in a recent work, gives the prevalent 
opinion among French physicists as follows :—“ Many explanations of this 
phenomenon have been offered, the most probable being that which considers 
it due to a group of bodies which form, as it were, a zone around the sun 
of solid asteroids, widely separated from one another, but occupying an 
enormous space, in the midst of which the earth is plunged ; aerolites and 
shooting stars will then be but isolated bodies belonging to this group, 
which, drawn within the sphere of the earth’s activity, fall upon its surface. 
According to this hypothesis, the Zodiacal Light will be due to reflected 
_ Solar light, and the absence of polarization which has been observed in it is 
a result of the light being reflected in all possible planes from the variously 
presented surfaces of this multitude of bodies.” —(Becquerel, La Lumière 
ses Causes et ses Effets, Tome L., p. 7, 1867.) Mr. Skey, as you are aware, 
