ar. 13, 1873] | 
at the present moment some indications that before long 
scientific men may return to this very problem ? 
Let us now advance a step. Whenit is found that we 
cannot conceive the negation of a proposition—that the 
subject and predicate cannot be separated in thought ; 
“then, indeed,” says Mr. Mill, “the inability to sepa- 
rate the two ideas proves their inseparable conjunction, 
here and now, in the mind which has failed in the 
attempt: but this inseparability in thought does 
not prove a corresponding inseparability in fact ; 
Nor even in the thoughts of other people, or of the 
same person in a possible future.” No matter for 
the present, how we come by our cognitions, this is 
surely admitting what Mr. Spencer calls the psychological 
necessity of thinking the proposition, In the next place, 
we must confess that we have never been able intelligibly 
to translate into the language of idealism those anti- 
realistic arguments that appeal to “fact” and to the 
experiences of “other people.” But, whatever may be 
meant by fact, and whatever may have a place in the 
minds of other people, it must for ever remain nothing 
to those in whose consciousness it can be neither pre- 
sented nor represented. Our science of numbers is not 
likely to be disturbed because it can be written in words 
that, perhaps in some inaccessible corner of the uni- 
verse, or in some mind of a different make from the 
human, twice two makes five. We have already exa- 
mined the examples given by Mr. Mill of propositions 
that have, as he thinks, passed from the condition of 
being inconceivable to that of being both conceivable and 
believed, and therefore we do not think it necessary to 
discuss the probability of any really simple and incon- 
ceivable proposition becoming conceivable in the mind 
of the ‘same person in a possible future.” 
We must pass to the next step in the argument as 
sketched above. Does reasoning rest on the postulate? 
Wecannot help thinking with regret that Mr. Mill has not 
felt it necessary to put forth his full strength on this point ; 
and we are by no means sure that we have grasped his 
full meaning. His words are :—“To say that when I 
apprehend that Ais B and that B is C, I cannot conceive 
that A is not C, is to my mind merely to say that I am 
compelled to believethat Ais C. If toconceive be taken 
in its proper meaning, viz., to form a mental representa- 
tion, I may be able to conceive A as not being C. After 
assenting with full understanding to the Copernican proof 
that it is the earth, and not the sun, that moves, I not only 
can conceive, or represent to myself, sunset as a motion 
of the sun, but almost everyone finds this conception of 
sunset easier to form than that which they nevertheless 
know to bz the true one.” This, as we understand it; 
seems open to the reply that, had sunset, considered as a 
motion of the sun, been inconceivable to begin with, no 
argument would have been needed to disprove it. Having 
followed the Copernican proof, we cease to believe that 
the sun moves, we remain, however, still able to conceive 
its doing so ; for though we cannot help believing that of 
which we cannot conceive the negation, it does not follow 
that we are unable to conceive the negation of everything 
that argument has compelled us to believe. But, whether 
by following a sound argument we are or are not rendered 
incapable of conceiving the reverse of the conclusion, has, 
NATURE 
359 
ee eee 
ing rests or does not rest on the postulate. To invalidate 
Mr, Spencer's argument by the method he has adopted, 
Mr. Mill would require to be able to represent in thought, 
not the sun moving through the heavens, in spite of the 
Copernican proof to the contrary but that at any step in 
the argument the conclusion need not follow from the 
premises. If he could do this he might still be convinced 
by argument, but we do not see how he must necessarily 
be so. Mr. Spencer’s contention is that reasoning rests 
on the postulate, not because a valid argument makes the 
reverse of the conclusion inconceivable, but because the 
axioms of logic have no higher warrant. 
Want of space forbids us entering further into the con- 
troversy. For the same reason we are unable to enter upon 
the inquiry whether we can properly be said to believe that 
of which we cannot form a mental representation, Mr. 
Spencer’s opinion is that we cannot, and accordingly 
“that anti-realelistic beliefs have never been held at all, 
They are but ghosts of beliefs, haunting those mazes of 
verbal propositions in which metaphysicians habitually 
lose themselves. Berkeley: was not an idealist ; he never 
succeeded in expelling the consciousness of an external 
reality, as we saw when analysing his language and his 
reasonings. Hume did not in the least doubt the existence 
of matter or of mind; he simply persuaded himself that 
certain arguments ought to make him doubt. Nor was 
Kant a Kantist: that space and time are nothing more 
than subjective forms was with him, as it has been and 
will be with every other, a verbally-intelligible proposition, 
but a proposition that can never be rendered into thought, 
and can never therefore be believed.” 
Douc.as A, SPALDING 
GEIKIE’S PRIMER OF PHYSICAL GEOGRAPHY 
Physical Geography. By Prof. Geikie. 
Series. (Macmillan.) 
ie must not be supposed that this is the Physical Geo- 
graphy which we have been expecting from Prof. 
Geikie. It is a little book of 110 pages, truly a primer, 
and only makes us more eager to get a larger work. 
The primer is written in a vivacious style ; the style 
of aman really interested in what he is talking to his 
readers about ; aud in all respects suitably written for its 
purpose. It would be a little too patronising if it were 
intended for any but the very young, who like being 
taken into the confidence of the writer, and spoken to 
as young friends. Itis to be hoped that a larger work 
may be equally vivacious and vigorous without this 
characteristic, which is, to repeat, not a fault in the 
primer, but would bea serious fault in the larger work 
intended for older boys and readers generally. Itis a 
fault that pervades Kingsley’s scientific books: it is a 
small annoyance at first, but finally “aggravates” one 
beyond all endurance. Moreover, the book is well illus- 
trated with new, good, and unconventional woodcuts, and 
is thoroughly well-arranged and printed. 
Now for its contents. After its introduction, which is 
in fact on “ eyes and no eyes,” we have the shape of the 
earth, day and night, the air, wind, vapour, dew, mist, 
rain, snow ; the circulation of water on the land, springs, 
hard and soft water, atmospheric denudation (in shorter 
Science Primer 
in reality, nothing to do with the question whether reason- | words than these), brooks, rivers, snow-fields, glaciers ; 
