10 Obfervations on Materialifm, the Ideal Sy/fen, eho, (Aug. 1, 
nal impreffions, or internal changes, and 
éonftitutine fenfation, is motion of fome 
fort or other, and particularly a vibratory 
motion inthe extremities, courfe, and origin 
of the nerves, isan opinion which, in com- 
mon with the zdeal /y/tem, has had fome. 
times to encounter the pleafantry, and 
fometimes to fuitain the infolence of ridi- 
cule. This opinion is neverthelefs ren- 
Gered to a certain degree probable by {e- 
veral facts relative to fenfation, of which 
an account may be {een in the writiogs of 
the mof eminent phyfiologifts.. In parti- 
cular, the late illuftrious and unrivalled 
Haller thus expreffes himfelf, ** Quid ergo 
ad mentem venit, et quomodo? Quando 
de fenfationibus nobis notisea detrahimus, » 
que habent pecuiiaria, ut ea fola {uperfint, 
quz habent communia, motus etit in 
mollem nervum impreflus. Et motum ad 
cerebrum venire credas, cum a fragore 
metallorum pulvere pyrio oneraterum 
commotiones in cerebro adeo manifelte et 
violente fuccedant: earum fimiles, que ab 
i€tu aliquo capiti ipfi infli€to fequuntur. 
Jrerum idem confirmatur exemplo fimilli- 
mez fcintille, et a filicis et chalybis vero 
conflifiu, et alterius imaginariz {cintillz, 
tum a frictione oculi nate, tum abfque 
oculi vitio, in epilepfia et convulfivis ma- 
lis. Motus ubique folus eft, qui et in ce- 
rebro mentem, et in objecti externi fenfa- 
tione nervum Jentientem adficit*.” But 
when the Exquirer aflerts that ‘a fenfation 
is a motion at the external extremity, and 
an idea a motion at the internal extremity 
_of the organ o ifenfe,”” if he means that in 
the cafe of fenfation the motion is confized 
to the external extremity, he afferts what 
will hardly be found confftent with the 
ftate of the fat, A divifion of the nerve 
or aligature on it will prevent the fenfa- 
tion (whatever be the impreffion) from 
being felt; that is, there will, in thefe - 
circumftanees, be no fenfation at all; 
while a very vivid feniation is often felt 
long after the external extremity of the 
organ hasbeen removed : a man who has 
lott his leg has often, from fome con- 
dition of the nerve in the ftump, been’ 
heard to complain of acute pain in the toe 
of the amputated limb. . 
4. The Exguirer fays, ‘* Ideas may be 
compared to a land{cape, and the mind | 
to the fun.” This comparifon, I believe, 
will hardly prove acceptable either io the 
foiritualit or to the materialit. The 
former,’ if he compare ideas to the land- 
feape, will compare the mind to the eye, 
which may be fhut or turned afice, and 
* Elem. Phyfiolog. vol. v. p. 530, 
confequently have the objects loft to it: 
the latter, if driven to explain his notion 
by fome fenfible image, will be little dif- 
pofed to admit of any powerful external 
agent, but will perhaps imbue what the 
Enquirer calls ‘the latent but produce- 
able forms,’’ with fomething like a phof- 
Phoric quality occafionally exerting itfelf 
and rendering vifible to the mental eye 
what was before unperceived and unper- 
ceivable: for the materialift willingly ac- 
cedes to that propofition of the idealift 
which afferts that ‘the exiftence of an 
idea confilts in its being perceived,”” and 
he is reluétantly forced to prefer the 
charge of great inconfiftency againft Hal- 
ler, who thus expreffes himilf on this ob- 
feure. fubje&. ‘* Diverlz ergo res funt: 
1. Objecta externa, cum fuis veris adtri- 
butis: 2.ecrum in fenfuum organa im- 
. preffiones : 3. harum impreflionum in cere- 
brum tranflatarum eftectus corporeus: 
4. hujus effectus in mente reprefentatio 
-.-+. Incipimus hic animam a corpore 
diftinguere ; quod enim in cerebro fit, id 
motus eft fibre medullaris: quod in ani- 
ma, .id eft-idea ab eo motu diverfiffima. 
Eam anima et habet fibi obverfantem, 
et omnino appercipit, nempe confcia eft 
fibi repraefentari ; motus interim alicujus, 
aut in, cerebro faéte2 mutationis, aut in 
Nervo, penitusignara... Nonomnes idee 
videntur apsercipi, fed ex fole, que paulo 
fortiores funt,’ aut minus per confuetudi- 
nem nobiscum familiares.’* Now if it 
be eflential to an idea that “ eam anima 
et habet fibi obverfantem, et omnino ap-~ 
percipit,’’ how can it be faid that ** non 
omnes idez videntur appercipz, fed ez fo- 
le, &c.? and how can this inconfiftency 
be avoided but by ending with the ‘¢ im- 
preffionum in cerebrum tranflatarum ef- 
teétus corporeus?”’ that is, the ‘* motus in 
cerebro fibre medullaris.” 
5. Where the Enquirer fays, ** Tdeas 
may exilt in a Jatent ftate during fleep or 
abfence of mind,’’ he affixes to the word 
idea a.different meaning from what I ap- 
prehend it will bear. It feems probable 
that the condition of the fenfory in fenfa- 
tion, the ** motus in cerebro fibre medul- 
laris,”? may admit of feveral gradations. 
The loweft degree’ may correfpond to the 
efiects of {uch external impreffions as are 
unhecded and unfelt, or to ** the latent 
but produceable forms” of the Exquirer : 
the next degree may conftitute what is 
properly called an zdea, that is a faint 
image of colour or vifible figure, or a 
fainter echo of fome diftinguifhable and 
* Elem, Phyfiolog. vol. v. p, 534- 
. appre- 
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