Indeed, there is no other way of
accounting for the variation in question. But again. The real diameter
of the same comet's nebulosity is observed to contract rapidly as it
approaches the sun, and dilate with equal rapidity in its departure
towards its aphelion. Was I not justifiable in supposing with M. Valz,
that this apparent condensation of volume has its origin in the
compression of the same ethereal medium I have spoken of before, and
which is only denser in proportion to its solar vicinity? The
lenticular-shaped phenomenon, also called the zodiacal light, was a
matter worthy of attention. This radiance, so apparent in the tropics,
and which cannot be mistaken for any meteoric lustre, extends from the
horizon obliquely upward, and follows generally the direction of the
sun's equator. It appeared to me evidently in the nature of a rare
atmosphere extending from the sun outward, beyond the orbit of Venus
at least, and I believed indefinitely farther.* Indeed, this medium
I could not suppose confined to the path of the comet's ellipse, or to
the immediate neighborhood of the sun.
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