Encyclopaedia Britannica, or, a Dictionary of arts, sciences, and miscellaneous literature : enlarged and improved. Illustrated with nearly six hundred engravings > Volume 13, MAT-MIC

2hap. V. M E T A P
vffociation nomena : For, granting the faft, it may ftill be afeed,
of Ideas VVhy does a pidturd lead our thoughts to the original;
— > or the mention of one apartment in a building introduce
an inquiry concerning the others ? To thefe quell ions
our author has given no anfwer; nor are we acquainted
with any writer who can be faid to have attempted it,
except Dr Hartley and his ingenious editor. There
may be fome of our readers whom the names of thefe
men will prejudice againlt their theory •, but, doubtlefs,
the greater part are willing to adopt truth, or to exa¬
mine an ingenious fpeculation, from whatever quarter it
comes. To fuch as feel themfelves otherwife difpofed,
we beg leave to fay, that it they allow the name of
. Priejlley to difguft them at what follows, they will
furnilh him with a new proof of the truth of the doctrine
94 which they reject.
I How they That ideas thould be aflbciated together, feems to
joperate. inevitable from the manner in which the mind ac¬
quires them. All our ideas, properly fpeaking, are
of fenfible objedts, and by far the greater part of them
of vijible objedts. But every fenlible objedt conveys
at once various fenfations and perceptions to the mind,
which appear not only united in fadt, but infeparable
in imagination. Thus, when a man looks at any par¬
ticular objedt, a tree for inltance, he perceives the
trunk, branches, leaves, Ji'&e, Jhape, and colour, &c. of
the whole at once : he does not lirlt perceive the Jigui e
of the trunk, then its Ji^e, then its colour, then ihe
branches, &c. all in fucceffion •, but a perception of the
whole is conveyed to the mind by one limultaneous
impreflion We have already feen, that the
fenfes, in fadt, convey nothing to the mind but their
refpedtive fenlations 5 and that the perception of the
external obiedt inftantly follows the fenfation. We
have like wife feen, that fenfation is occalioned by
fome impreflion, concuflion, or vibration, given to
the nerves and brain, and by them communicated to
the mind or percipient being. We have like wife feen,
that memory depends as much upon the brain as ori¬
ginal fenfation, and is always attended or occafioned
by fimilar concuflions or vibrations, &c. I hefe are
fadts proved by univerfal experience, and which, we
believe, no thinking man has ever called in queftion.
It follows, therefore, that every adtual fenfation muft
leave fome effedl in the brain, either an adtual print,
which feems to be impoflible, or a tendency to vibrate
or be agitated in the fame way as when the original
impreflion was made. Fliis being the cafe, it is na¬
tural to conclude, that when any part of the original
perception is revived in the memory, the whole per¬
il Y S I C S.
589
ception fhould be revived at once, fo as that we cannot A®j0-j““n
have an idea of the trunk of a tree without perceiving , 0 ‘ j
the ideas of the branches affociated with it. This is
indeed not merely natural, but the contrary feems to
be impoflible ; for as the original agitation or vibra¬
tion was occationed by the whole tree, it is evident,
that whatever effedt or tendency that agitation or
vibration left behind it, muft be left by the whole vi¬
bration, and therefore be equally related to the whole
tree.
But no objedt Hands Angle in nature. When we
view a tree, or any thing elfe, we always notice, how¬
ever tranuently, the fteld where it grows and the ob¬
jedts around it. Thefe too leave ehedts in the brain
at the fame time that the tree does fo} and therefore
make their appearance with it in the memory or ima¬
gination : but if the tree was the objedt to which we
principally attended during the adtual fenfation, the
idea of it will be much more vivid than the idea of its
adjuncts, and remain much longer in the imagination
or memory 5 becaufe the original fenfation by which it
was perceived, was ftruck much deeper than the fen¬
fations by which its adjundts were perceived. All
this muft be intelligible to every one who attends to
what we have already faid of fenfation, perception, and
memory.
Thus we fee why a pidture leads our thoughts tc-
the original, and why the mention of one apartment
in a building introduces an inquiry concerning the
others. It is not merely becaufe the pidture refembles
the original, and becaufe the apartments of a building
are contiguous. Between a plain furface, variouily co¬
loured and fttaded, and the contour of the human
face, there is certainly very little real refemblance, as
any man may be convinced who places his eye with¬
in Ax inches of a good pidture. But the painter, hav¬
ing by his Ikill in perfpedtive, contrived to lay his
colours on the plain canvas in fuch a manner as that
they refledt the fame rays of light with the original,
provided the fpedtator Hand at the proper diftance j
thefe rays proceeding from the pidture fall upon the eye
in the fame diredtion, and therefore give to the nerves
and brain the very fame impulfe which was given by
the original. When one apartment of a building is
mentioned, we inquire concerning the others from the
very fame caufe that, when we think of the trunk of
a tree which we have feen, we cannot avoid thinking
likewife of its branches. 95
But the principle of aflbeiation takes place among Affociation
things not naturally conne&ed, as the apartments of
a words of
language:
(o ) This is certainly the cafe with adults, but it may be doubted whether it be fo with very young c 1 -
dren. ^ It has been fhown already, that the fenfation communicated by the eye from any viAble objedt, has
not the leaft refemblance to that objeft •, and that in looking at a tree or any thing elfe, a full-grown man
pays not the leaft attention to the appearance which the tree really makes to his eye ; nay, that he is no ev en
confcious of that appearance farther than as it conAfts in colour. It is by the fenfe °f touch only rat
acquire ideas of Agure, even of plain Agure; and we imagine that we perceive them by the eye only be¬
caufe different Agures, as diftinguilhable by touch, are fo clofely affociated with their correfpondmg vi-
flble fenfations, that long before we are capable of inquiry, thefe two things are infeparable m the imag-
nation. It is otherwife with children, who, when they Arft begin to diftinguifti objedts by the fenfe of g ,
appear to do it, with great deliberation, as if they Arft felt the proper fenfation of light and ^ °ur fo °r Jo
modifled, and afterwards acquired, by fomething like a mental inference, a notion of the figure at which t J
are looking.