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PHENOMENA OF THE ZODIACAL LIGHT. 495 
although such an effect might be produced by a periodical alteration in the size 
and general lustre of the body, still the supposition of such a rapid material change 
in so large a member of the solar system, is extremely improbable: whilst this 
body’s revolving may be held to be necessary according to the principles of gravi- 
tation ; for otherwise the component particles would speedily fall into the sun ; and 
that some portions are brighter than others, follows partly as a consequence of the 
observed unequal size of the two sides. Were the light stationary, then the 
greatest and least lengths and brightnesses should occur at the same time in suc- 
cessive years, because on arriving again at the same points of its orbit, the earth 
should again see the same parts of the zodiacal light pointing to the same direc- 
tion in space; but, as already stated, the contrary to this has been observed. 
The greatest elongation observed was 79°, and the least 50°, but from the 
‘varying circumstances and positions in which the observations were made, the 
short period of time over which they extend, together with the small number of 
favourable opportunities, and the distance of the place from the equator, which 
these conditions afforded, no numerical results of much accuracy can be derived 
from them alone; but some advantage may be gained by comparing them with 
the results of former observers. 
The number, however, of these, 7. ¢., of actual observers, is comparatively 
small, and they are all very recent; for, strange to say, no notice of the zodiacal 
light is found amongst the writings of astronomers or natural philosophers until 
1661. And indeed, when we consider that this phenomenon may be generally 
described as a broad and tall light seen in the western sky after sunset, and in 
the eastern before sunrise, with a length of about 60°, a breadth of 20°, combining 
with a brightness nearly equal to that of the milky way, a regular mathematical 
figure, which makes it far more remarkable, and rising, as it does, at a greater 
angle to the horizon, so as to be better seen in countries nearer the equator than 
ourselves, and being probably of as great antiquity as the sun itself,—truly it is 
astonishing that all these notabilia should have been passed over in the earlier 
ages of the world, when civilization flourished more to the south, and the men of 
ancient Athens and Babylon lived under a clear sky, in a genial climate, which 
invited rather than forbade the contemplation of the firmament by night. It re- 
‘mained, however, for the inhabitants of these cloud-vexed northern islands to be 
the first to take notice of the phenomenon, and so supply another instance of the 
indomitable perseverance of an iron race overcoming all the untoward obstacles 
of an unpropitious position, and rising superior to other races revelling in the 
most luxurious advantages of nature. 
Claims have been put up for Kepter and Descartes, as being the original 
discoverers of the zodiacal light; but the passages in their respective works* 
* Keprer’s Hpit. Astron. Copernicane, t.i., p. 57; and t. ii., p. 898 ; Descarrzs, Principes, iii., 
Art. 136, and 137. 
