PHILOSOPHY, MENTAL. 
can add up a column of figures, knows the 
nature of the operation, because it is learnt 
after the memory has acquired consider- 
able power. The sum of two or three fi- 
gures is first ascertained : the ideal Change 
of that sum must of course be in the mind, 
and with that sum is combined the next 
figure, which forms a new sum, and so on. 
Now then there is the act of adding a num- 
ber, the ideal change of which is in the 
mind, to another number of which there is 
a sensible change, and there is the ideal 
change of the sum, and so on, continually 
recurring ; this we perceive when we are 
trying to add up slowly. But persons who 
are veiy familiar with such additions, will 
tell the result or final sum, apparently with- 
out an eflFort, apparently without the inter- 
vention of the mind, and certainly without 
any consciousness of the operations and 
ideal changes which must have passed in 
the mind before the result could have been 
obtained. It will not unfrequently he found, 
that persons very much habituated to these 
operations, can add up much more cor- 
rectly while they leave themselves uncon- 
scious of the operations and ideal changes, 
than when they are conscious of them : and, 
what appears to us to settle the point, as 
far as consciousness is concerned, persons 
who by constant custom have become fa- 
miliar with all possible combinations of 
small numbers, can go through a series of 
additions, and at the same time closely en- 
gage the attention upon another object; 
for instance, can dictate one or more let- 
ters. — As to inotory changes, the fact is so 
obvious, that muscular actions, which must 
have their origin in the mind, as being re- 
gulated by impressions upon the external 
organs of sense, go on in long succession, 
and with frequent variation, while at the 
same time the attention is fully occupied by 
some object of thought, that we should be 
ready to suppose nothing but opposition to 
a pre-formed hypothesis, could lead a per- 
son to doubt whether in such cases the mus- 
cular action excited the consciousness. 
Such an immense variety of muscular ac- 
tions are continually taking place, in cases 
in which volition was once concerned, with- 
out in any way whatever attracting the no- 
tice of the mind, and this is so obvious a 
fact, and so satisfactorily accounted for by 
Hartley, that however plausible the coun- 
ter-considerations of the great northern phi- 
losopher, Dugald Stewart, (see Elements, 
Chap, ii.) we cannot suppose that they can 
gain admission where the principle of asso- 
ciation is thoroughly understood. 
13. If this distinction between sensible 
and ideal changes, and sensations and ideas, 
be just ; or rather, if the existence of sen- 
sorial changes, without consciousness, be 
admitted, (and we more and more feel satis- 
fied that it is a fact, and if so, a very im- 
portant one in our mental frame), then the 
four preceding faculties, or capacities of the 
mind, are to be referred to the sbnsorium, 
and are, in reality, the properties or powers 
of the mental organs. We feel disposed to 
admit, that the sensorium is the raedullaiy 
substance of the brain; but we beg our 
readers to bear in mind, that what we have 
advanced is entirely independent of this 
opinion, and that indeed it is rather clogged 
by it. We use the terms sensorium and 
mental Organs, because, in our opinion, they 
tend to give greater distinctness to our re- 
flections on what passes within us ; but it is 
with no view to decide whether they are ma- 
terial or immaterial.— Consciousness, or the 
percipient faculty, we consider as a distinct 
faculty from those already mentioned ; it is 
the faculty or capacity by which the mind 
is affected by sensorial changes, whether 
sensible, ideal, or motory. Consciousness 
is in fact the notice of the mind itself; and 
the term is applied to that state with which 
every sensorial change which excites the 
notice of the mind is attended. — When the 
consciousness is continued, either on a par- 
ticular object, or on a particular succession 
of objects, whether or not that continu- 
ance is caused by volition, the state of the 
mind is called attention.— It is by con- 
sciousness alone that we have any know- 
ledge of the other powers of the mind ; and 
when directed to their operations, the ap- 
pellation is peculiarly appropriate. When 
it is excited by sensible changes, it is usually 
called perception : consciousness referring 
to the operations of the mind, as such ; per- 
ception to them as produced by external 
objects. (For an account of perceptions, as 
distinct- from sensations, see Sensation.) 
We are conscious of ideas and sensations; 
we perceive the external objects which 
produce impressions on the external organs. 
When the consciousness is suspended, as it 
often is, during sleep, &c. the ever active 
mechanism of the mental organs proceeds ; 
in such cases, its operations sometimes ex- 
cites the consciousness; otherwise we know 
of their existence only by their effects. On 
the other hand, consciousness necessarily 
implies sensorial changes ; for to speak of 
the consciousness of nothing is an ab- 
sindity. 
