Theories of the Aether Articles relating to the Emergence of Scientific Theories of the Cosmic Aether
On the hypothesis of the _plenum_ Introductory Lecture on Experimental Physics (1871?). James Clerk Maxwell
Web Publication by Mountain Man Graphics, Australia - Southern Winter 2004

Introduction

"On the _plenum" (ie: aether)

Introductory Lecture on Experimental Physics
James Clerk Maxwell. (1871?)

Is it true then that our scientific speculations have really
penetrated beneath the visible appearance of things, which seem to be
subject to generation and corruption, and reached the entrance of that
world of order and perfection, which continues this day as it was
created, perfect in number and measure and weight?

We may be mistaken.  No one has as yet seen or handled an individual
molecule, and our molecular hypothesis may, in its turn, be supplanted
by some new theory of the constitution of matter; but the idea of the
existence of unnumbered individual things, all alike and all
unchangeable, is one which cannot enter the human mind and remain
without fruit.

But what if these molecules, indestructible as they are, turn out to
be not substances themselves, but mere affections of some other
substance?

According to Sir W. Thomson's theory of Vortex Atoms, the substance of
which the molecule consists is a uniformly dense _plenum_, the
properties of which are those of a perfect fluid, the molecule itself
being nothing but a certain motion impressed on a portion of this
fluid, and this motion is shewn, by a theorem due to Helmholtz, to be
as indestructible as we believe a portion of matter to be.

If a theory of this kind is true, or even if it is conceivable, our
idea of matter may have been introduced into our minds through our
experience of those systems of vortices which we call bodies, but
which are not substances, but motions of a substance; and yet the idea
which we have thus acquired of matter, as a substance possessing
inertia, may be truly applicable to that fluid of which the vortices
are the motion, but of whose existence, apart from the vortical motion
of some of its parts, our experience gives us no evidence whatever.

It has been asserted that metaphysical speculation is a thing of the
past, and that physical science has extirpated it.  The discussion of
the categories of existence, however, does not appear to be in danger
of coming to an end in our time, and the exercise of speculation
continues as fascinating to every fresh mind as it was in the days of
Thales.


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