The Works of Edgar Allan Poe — Volume 1

By Edgar Allan Poe

Page 36

in point of fact, an ascension being made to any given altitude,
the ponderable quantity of air surmounted in any farther ascension is
by no means in proportion to the additional height ascended (as may
be plainly seen from what has been stated before), but in a ratio
constantly decreasing. It is therefore evident that, ascend as high as
we may, we cannot, literally speaking, arrive at a limit beyond which
no atmosphere is to be found. It must exist, I argued; although it may
exist in a state of infinite rarefaction.

"On the other hand, I was aware that arguments have not been wanting
to prove the existence of a real and definite limit to the atmosphere,
beyond which there is absolutely no air whatsoever. But a circumstance
which has been left out of view by those who contend for such a limit
seemed to me, although no positive refutation of their creed, still
a point worthy very serious investigation. On comparing the intervals
between the successive arrivals of Encke's comet at its perihelion,
after giving credit, in the most exact manner, for all the disturbances
due to the attractions of the planets, it appears that the periods are
gradually diminishing; that is to say, the major axis of the comet's
ellipse is growing shorter, in a slow but perfectly regular decrease.
Now, this is precisely what ought to be the case, if we suppose a
resistance experienced from the comet from an extremely rare ethereal
medium pervading the regions of its orbit. For it is evident that such
a medium must, in retarding the comet's velocity, increase its
centripetal, by weakening its centrifugal force. In other words, the
sun's attraction would be constantly attaining greater power, and the
comet would be drawn nearer at every revolution. 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

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