ch it was invariably consequent, it was more rational
to suppose that our inability to assign the causes of
other phenomena arose from our ignorance, than that
there were phenomena which were uncaused, and which
happened accidentally to be exactly those which we had
hitherto had no sufficient opportunity of
studying."--Vol. II. p. 108.

_Hypotheses._--Mr Mill's observations on the use of hypotheses in
scientific investigation, except that they are characterized by his
peculiar distinctness and accuracy of thought, do not differ from the
views generally entertained by writers on the subject. We are induced
to refer to the topic, to point out what seems to us a harsh measure
dealt out to the undulatory theory of light--harsh when compared with
the reception given to a theory of Laplace, having for its object to
account for the origin of the planetary system.

We had occasion to quote a passage from Mr Mill, in which he remarks
that the majority of scientific men seem not yet to have completely
got over the difficulty of conceiving matter to act (contrary to the
old maxim) where it is not; "for though," he says, "they have at last
learned to conceive the sun _attracting_ the earth without any
intervening fluid, they cannot yet conceive the sun _illuminating_ the
earth without some such medium." But it is not only this difficulty
(which doubtless, however, is felt) of conceiving the sun illuminating
the earth without any medium by which to communicate its influence,
which leads to the construction of the hypothesis, either of an
undulating ether, or of emitted particles. The analogy of the other
senses conducts us almost irresistibly to the imagination of some such
medium. The nerves of sense are, apparently, in all cases that we can
satisfactorily investigate, affected by contact, by impulse. The nerve
of sight itself, we know, when touched or pressed upon, gives out the
sensation of light. These reasons, in the first place, conduct us to
the supposition of some medium, having immediate communication with
the eye; which medium, though we are far from saying that its
existence is established, is rendered probable by the explanation it
affords of optical phenomena. At the same time it is evident that the
hypothesis of an undulating ether, assumes a fluid or some medium, the
existence of which cannot be directly ascertained. Thus stands the
hypothesis of a luminiferous ether--in what must be allowe