i 
220 F’. A. P. Barnard on the Zodiacal Light. 
mainly from the want of plausibility in any other, and depends 
upon a series of exclusions, of which the very first in order is 
decidedly not established. 
he evidence of the truth of his second proposition is found 
by Mr. Jones, in the fact that a zodiacal light was visible to him 
in the east and the west at the same time, when the sun was de- 
ninety degrees below the horizon. That neither of these 
lights could have been reflected from a ring interior to the 
earth’s orbit, is obvious. 
The third proposition is regarded as established by the consid- 
erable changes which the lateral boundaries of the light undergo, 
as the position of the observer to the ecliptic ‘Is altered by the 
earth’s diurnal motion; these changes being too great to spring 
from such a cause, if we refer the source of the light to a dis- 
tance of more than 190,000,000 of miles, as we must do if we 
attribute it to a ring external to the earth’s orbit. An argument 
more decisive than this, and to the same effect, would seem to 
be deducible from the fact that, if such were the source of the 
light, it ought to be vastly brighter in the quarter of the heav- 
ens opposite to the sun, than in that where it is in fact seen. 
The positive evidence confirmatory of the truth of the hypoth- 
esis of a ring concentric with the earth, is embraced in these 
three facts :— 
1. In low latitudes, the light is visible throughout the year. 
2. To an observer who has the ecliptic vertical at midnight, 
the light appears both in the east and in the west, at the same 
time 
3. The moon appears occasionally to produce a zodiacal light. 
Having thus stated the grounds on which the theory of the 
zodiacal light proposed by Mr. Jones rests, it is in order to con- 
sider the difficulties which this theory suggests. These are the 
following : 
1, The aspect of the light itself is not such asa ring ought 
to present. 
2. The axis of the light undergoes no parallactic displacement, 
however great be the observer’s change of position; and the ex 
planation offered of this difficulty by Mr. Jones is not satisfactory- 
. The geometrical inferences to which the hypothesis legit!” 
mately leads, as they are deduced from different observations ate 
inconsistent WEEh- : ; 
4. To adopt the supposition of a nebulous ring surrounding 
the earth in order to explain the phenomena which are actually 
observed, involves unavoidably a necessity that other still more 
striking phenomena should present themselves, which are never 
) ¢ n more particularly what is intended by the first of 
remar 
positions, we may e appearance of a rpg 
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