222 F. A. P. Barnard on the Zodiacal Light. 
other part Q’Q, in which the brightness decreases upward. 
hat then can we conclude, if we adopt the ring theory, but 
that the point Q’, where the tangent, SW, meets the lower sur- 
face of the ring, is itself in the horizon or below it? But at the 
close of twilight this same tangent (when the light happens to 
é in the vertical passing through the sun, as it is occasionally in 
low latitudes) intersects the upper stratum of the atmosphere 
preeisely in the horizon; and hence, so far as the mere aspect of 
the light can furnish a basis of argument, we are forced to con- 
clude, that if the brightness is a reflection from a body concen- 
tric with the earth, this body cannot be one having any sensible 
interval intervening between it and the atmosphere.* 
absence of a parallax appears, secondly, to furnish a seri- 
ous objection to the ring theory. Mr. Jones’s mode of explaining 
away this difficulty is ingenious, but it will hardly bear examina- 
tion. He supposes the ring to have considerable breadth, and 
that the locus of the light (or more properly of its axis) is differ- 
ent for different observers ; being in all cases in a plane passing 
through the eye, parallel to the ecliptic. Mr. Jones seems to look 
upon this as an optical necessity; but apparently without suffi- 
cient reason. In the first place, it is probable that the supposed neb- 
ulous ring, if visible at all, would be visible throughout its whole 
breadth, and would present no sensible lateral variation of bright- 
ness. Secondly, should such a body exhibit an axis of maximum 
brightness, this axis would not be of necessity, nor usually, pat- 
allel to the ecliptic. he case is by no means that of a cylin- 
drically concave solid reflector. In that case, parallel rays at 
right angles to the axis of the cylinder, would undoubtedly be re- 
each particle is an independent reflector, the intensity of the light 
which it throws to the eye being unaffected by the neighborhood 
ent does not suppose the reflection specular, as Mr. Jones claims— 
ection which reuiies a polished surface to the particles of the nebula. 
