Thomas Reid.

The works of Thomas Reid, D.D.; now fully collected, with selections from his umpublished letters online

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as well as we can, what notion he would
have of visible objects, and what conclu-
sions he would deduce from them. We
must not conceive him disposed by his con-
stitution, as we are, -to consider the visi-
ble appearance as a sign of something else :
it is no sign to him, because there is no-
thing signified by it ; and, therefore, we must
suppose him as much disposed to attend to
the visible figure and extension of bodies,
as we are disposed to attend to their tangi-
ble figure and extension.

If various figures were presented to his
sense, he might, without doubt, as they
grow familiar, compare them together, and
perceive wherein they agree, and wherein
they differ. He might perceive visible ob-
jects to have length and breadth, but could
have no notion of a third dimension, any
more than we can have of a fourth.* All
visible objects would appear to be termi-
nated by lines, straight or curve ; and ob-
jects terminated by the same visible lines,
would occupy the same place, and fill the
same part of visible space. It would not
be possible for him to conceive one object
to be behind another, or one to be nearer,
another more distant.

To us, who conceive three dimensions, a
line may be conceived straight ; or it may
be conceived incurvated in one dimension,

* This proceeds upon the supposition that our no.
ion ot space is merely empirical. — H.

and straight in another ; or, lastly, it may
be incurvated in two dimensions. Suppose
a line to be drawn upwards and downwards,
its length makes one dimension, which we
shall call upwards and downwards ; and
there are two dimensions remaining, accord-
ing to which it may be straight or curve.
It may be bent to the right or to the left ;
and, if it has no bending either to right or
left, it is straight in this dimension. But
supposing it straight in this dimension of
right and left, there is still another dimen-
sion remaining, in which it may be curve ;
for it may be bent backwards or forwards.
When we conceive a tangible straight line,
we exclude curvature in either of these two
dimensions : and as what is conceived to be
excluded, must be conceived, as well as
what is conceived to be included, it follows
that all the three dimensions enter into our
conception of a straight line. Its length
is one dimension, its straightness in two
other dimensions is included, or curvature
in these two dimensions excluded, in the
conception of it.

The being we have supposed, having no
conception of more than two dimensions, of
which the length of a line is one, cannot
possibly conceive it either straight or curve
in more than one dimension ; so that, in his
conception of a right line, curvature to the
right hand or left is excluded ; but curva-
ture backwards or forwards cannot be ex-
cluded, because he neither hath, nor can
have any conception of such curvature.
Hence we see the reason that a line, which
is straight to the eye, may return into itself ;
for its being straight to the eye, implies only
straightness in one dimension ; and a line
which is straight in one dimension may,
notwithstanding, be curve in another dimen-
sion, and so may return into itself.

To us, who conceive three dimensions, a
surface is that which hath length and
breadth, excluding thickness ; and a surface
may be either plain in this third dimension,
or it may be incurvated : so that the notion
of a third dimension enters into our concep-
tion of a surface ; for it is only by means
of this third dimension that we can dis-
tinguish surfaces into plain and curve sur-
faces ; and neither one nor the other can
be conceived without conceiving a third

The being we have supposed, having no
conception of a third dimension, his visible
figures have length and breadth indeed;
but thickness is neither included nor ex-
cluded, being a thing of which he has no
conception. And, therefore, visible figures,
although they have length and breadth, as
surfaces have, yet they are neither plain
surfaces nor curve surfaces. For a curve
surface implies curvature in a third dimen-
^ sion, and a plain surface implies the want



of curvature in a third dimension ; and
such a being can conceive neither of these,
because he has no conception of a third
dimension. Moreover, although he hath a
distinct conception of the inclination of two
lines which make an angle, yet he can
neither conceive a plain angle nor a spher-
ical angle. Even his notion of a point is
somewhat less determined than ours. In
the notion of a point, we exclude length,
breadth, and thickness ; he excludes length
and breadth, but cannot either exclude or
include thickness, because he hath no con-
ceptual of it.

Having thus settled the notions which
nich a being as we have supposed might
form of mathematical points, lines, angles,
Jind figures, it is easy to see, that, by com-
paring these together, and reasoning about
them, he might discover their relations, and
form geometrical conclusions built upon
self-evident principles. He might likewise,
without- doubt, have the same notions of
numbers as we have, and form a system of
arithmetic. It is not material to say in
what order he might proceed in such dis-
coveries, or how much time and pains he
might employ about them, but what such
a being, by reason and ingenuity, without
any materials of sensation but those of
sight only, might discover.

As it is more difficult to attend to a de-
tail of possibilities than of facts, even of
slender authority, I shall beg leave to give
an extract from the travels of Johannes
Rudolphus Anepigraphus, a Rosicrucian
philosopher, who having, by deep study of
the occult sciences, acquired the art of
transporting himself to various sublunary re-
gions, and of conversing with various orders
of intelligences, in the course of his adven-
tures became acquainted with an order of
beings exactly such as I have supposed.

How they communicate their sentiments
to one another, and by what means he be-
came acquainted with their language, and
was initiated into their philosophy, as well
as of many other particulars, which might
have gratified the curiosity of his readers,
and, perhaps, added credibility to his rela-
tion, he hath not thought fit to inform us ;
these being matters proper for adepts only
to know.

His account of their philosophy is as fol-
lows : —

" The Idomenians," saith he, " are many
of them very ingenious, and much given to
contemplation. In arithmetic, geometry,
metaphysics, and physics, they have most
elaborate systems. In the two latter, in-
deed, they have had many disputes carried
on with great subtilty, and are divided in-
to various sects ; yet in the two former
there hath been no less unanimity than
among the human species. Their prinei- ,

pies relating to numbers and arithmetic,
making allowance for their notation, differ
in nothing from ours — but their geometry
differs very considerably."

As our author's account of the geometry
of the Idomenians agrees in everything
with the geometry of visibles, of which we
have already given a specimen, we shall
pass over it. He goes on thus : — " Colour,
extension, and figure, are conceived to be
the essential properties of body. A very
considerable sect maintains, that colour is
the essence of body. If there had been no
colour, say they, there had been no percep-
tion or sensation. Colour is all that we
perceive, or can coneeive, that is peculiar
to body ; extension and figure being modes
common to body and to empty-space. And
if we should suppose a body to be annihi-
lated, colour is the only thing in it that can
be annihilated ; for its place, and conse-
quently the figure and extension of that
place, must remain, and cannot be imagined
not to exist. These philosophers hold space
to be the place of all bodies, immoveable and
indestructible, without figure, and similar
in all its parts, incapable of increase or di-
minution, yet not unmeasurable ; for every
the least part of space bears a finite ratio to
the whole. So that with them the whole
extent of space is the common and natural
measure of everything that hath length and
breadth ; and the magnitude of every body
and of every figure is expressed by its being
such a part of the universe. In like manner,
the common and natural measure of length
is an infinite right line, which, as hath been
before observed, returns into itself, and hath
no limits, but bears a finite ratio to every
other line.

"As to their natural philosophy, it is
now acknowledged by the wisest of them to
have been for many ages in a very low
state. The philosophers observing, that
body can differ from another only in colour,
figure, or magnitude, it was taken for
granted, that all their particular qualities
must arise from the various combinations
of these their essential attributes ; and,
therefore, it was looked upon as the end ot
natural philosophy, to shew how the various
combinations of these three .qualities in dif-
ferent bodies produced all the phenomena
of nature. It were endless to enumerate
the various systems that were invented with
this view, and the disputes that were car-
ried on for ages ; the followers of every
system exposing the weak sides of other
systems, and palliating those of their own,
with great art.

" At last, some free and facetious spirits,
wearied with eternal disputation, and the
labour of patching and propping weak sys-
tems, began to complain of the subtilty" of
nature ; of the infinite 1 changes that bodies



-ndergo in figure, colour, and magnitude ;
and of the difficulty of accounting for these
appearances— making this a pretence for
giving up all inquiries into the causes of
things, as vain and fruitless.

" These wits had ample matter of mirth
and ridicule in the systems of philosophers ;
and, finding it an easier task to pull down
than to build or support, and that every
sect furnished them with arms and auxi-
liaries to destroy another, they began to
spread mightily, and went on with great
success. Thus philosophy gave way to scep-
ticism and irony, and those systems which
had been the work of ages, and the admira-
tion of the learned, became the jest of the
vulgar : for even the vulgar readily took
part in the triumph over a kind of learning
which they had long suspected, because it
produced nothing but wrangling and alter-
ed, ion. The wits, having now acquired
great reputation, and being flushed with
success, began to think their triumph in-
complete, until every pretence to know-
ledge was overturned ; and accordingly
began their attacks upon arithmetic, geo-
metry, and even upon the common notions
of untaught Idomenians. So difficult it
hath always been," says our anthor, "for
great conquerors to know where to stop.

" In the meantime, natural philosophy
began to rise from its ashes, under the
direction of a person of great genius, who is
looked upon as having had something in him
above Idomenian nature. He observed,
that the Idomenian faculties were certainly
intended for contemplation, and that the
works of nature were a nobler subject to
exercise them upon, than the follies of sys-
tems, or the errors of the learned ; and
being sensible of the difficulty of finding out
the causes of natural things, he proposed,
by accurate observation of the phsenomena
of nature, to find out the rules according to
which they happen, without inquiring into
the causes of those rules. In this he made
considerable progress himself, and planned
out much work for his followers, who call
themselves inductive philosophers. The
sceptics look with envy upon this rising
sect y as eclipsing their reputation, and
threatening to limit their empire ; but they
are at a loss on what hand to attack it.
The vulgar begin to reverence it as pro-
ducing useful discoveries.

" It is to be observed, that every Idome-
nian firmly believes, that two or more bo-
dies may exist in the same place. For this
they have the testimony of sense, and they
can no more doubt of it, than they can
doubt whether they have any perception at
all. They often see two bodies meet and
coincide in the same place, and separate
again, without having undergone any
change in their sensible qualities hi thi i

penetration. When two bodies meet, and
occupy the same place, commonly one onlj
appears in that place, and the other disap-
pears. That which continues to appear is
said to overcome, the other to be over-

To this quality of bodies they gave a
name, which our author tells us hath no
word answering to it in any human lan-
guage. And, therefore, after making a
long apology, which I omit, he begs leave
to call it the overcoming quality of bodies.
He assures us, that "the speculations which
had been raised about this single quality of
bodies, and the hypotheses contrived to ac-
count for it, were sufficient to fill many
volumes. JNor have there been, fewer hy-
potheses invented by their philosophers, to
account for the changes of magnitude and
figure; which, in most bodies that move,
they perceive to be in a continual fluctua-
ation. The founder of the inductive sect,
be ieving it to be above the reach of Ido-
menian faculties, to discover the real causes
of these phsenomena, applied himself to
find from observation, by what laws they
are connected together ; and discovered
many mathematical ratios and relations con-
cerning the motions, magnitudes, figures,
and overcoming quality of bodies, which
constant experience confirms. But the op-
posers of this sect choose rather to content
themselves with feigned causes of these
phsenomena, than to acknowledge the real
laws whereby they are governed, which
humble their pride, by being confessedly

Thus far Johannes Eudolphus Anepigra-
phus. Whether this Anepigraphus be the
same who is recorded among the Greek
alchemistical writers not yet published, by
Borrichius, Fabricius, and others," I do
not pretend to determine. The identity of
their name, and the similitude of their
studies, although no slight arguments, yet
are not absolutely conclusive. Nor will I
take upon me to judge of the narrative of
this learned traveller, by the external marks
of his credibility ; I shall confine myself to
those which the crit cs call internal. It .
would even be of small importance to in-
quire, whether the Idomenians have a real,
or only an ideal existence ; since this is
disputed among the learned with regard to
things with which we are more nearly con-
nected. The important question is, whe-
ther the account above given, is a just ac-
count of their geometry and philosophy ?
We have all the faculties which they

* This is true ; the name is not imaginary
"Anepigraphus the Philosopher'' is i he Tepuled author
of several chemical treatises in Greek, which have not
as *yet been deemed worthy of publicatinn. .See
Du Cange, " Gloss, med. etinf.* Gramtatis," voce
n«*;Tvs. and Reiiit'su, " Var. I.ectt " L 11. c. a.
— H.



have, with the addition of others which
they have not ; we may, therefore, form
some judgment of their philosophy and ge-
ometry, by separating from all others, the
perceptions we have by sight and reasoning
upon them. As far as I am able to judge
in this way, after a careful examination, their
geometry must be such as Anepigraphus
hath described. Nor does his account of
their philosophy appear to contain any evi-
dent marks of imposture ; although here,
no doubt, proper allowance is to be made
for liberties which travellers take, as well as
for involuntary mistakes which they are apt
to fall into.

Section X.


Having explained, as distinctly as we
can, visible figure, and shewn its connection
with the things signified by it, it will be
proper next to consider some phsenomena
of the eyes, and of vision, which have com-
monly been referred to custom, to anato-
mical or to mechanical causes ; but which,
as I conceive, must be resolved into origi-
nal powers andprinciples of thehumanmind;
and, therefore, belong properly to the sub-
ject of this inquiry.

The first is the parallel motion of the
eyes ; by which, when one eye is turned
to the right or to the left, upwards or down-
wards, or straight forwards, the other
always goes along with it in the same direc-
tion. We see plainly, when both eyes are
open, that they are always turned the same
way, as if both were acted upon by the same
motive force ; and if one eye is shut, and the
hand laid upon it, whi'e the other turns
various ways, we feel the eye that is shut
turn at the same time, and that whether
we will or not. What makes this pheno-
menon surprising is, that it is acknowledged,
by all anatomists, that the muscles which
move the two eyes, and the nerves which
serve these muscles, are entirely distinct
and unconnected. It would be thought
very surprising and unaccountable to see a
man, who, from his birth, never moved
one arm, without moving the other pre-
cisely in the same manner, so as to keep
them always parallel— yet it would not be
more difficult to find the physical cause of
such motion of the arms, than it is to find
the cause of the parallel motion of the eyes,
which is perfectly similar.

The only cause that hath been assigned
of this parallel motion of the ejes, is cus-
tom. We find by experience, it is said,
when we begin to look at objects, that, in
order to have distinct vision, it is necessary
to turn both eyes the same way j therefore,

we soon acquire the habit of doing it con-
stantly, and by degrees lose the power of
doing otherwise.

This account of the matter seems to be
insufficient ; because habits are not got at
once ; it takes time to acquire and to con-
firm them ; and if this motion of the eyes
were got by habit, we should see children,
when they are born, turn their eyes different
ways, and move one without the other, as
they do their hands or legs. I know some
have affirmed that they are apt to do so.
But I have never found it true from my
own observation, although I have taken
pains to make observations of this kind, and
have had good opportunities. I have
likewise consulted experienced midwives,
mothers, and nurses, and found them agree,
that they had never observed distortions
of this kind in the eyes of children, but
when they had reason to suspect convul-
sions, or some preternatural cause.

It seems, therefore, to be extremely pro-
bable, that, previous to custom, there is
something in the constitution, some natural
instinct, which directs us to move both eyes
always the same way.*

We know not how the mind acts upon
the body, nor by what power the muscles
are contracted and relaxed — but we sec
that, in some of the voluntary, as well as
in some of the involuntary motions, this
power is so directed, that many muscles
which have no material tie or connection-f-
act in concert, each of them being taught
to play its part in exact time and measure.
Nor doth a company of expert players in
a theatrical performance, or of excellent
musicians in a concert, or of good dancers
in a country dance, with more regularity
and order, conspire and contribute their
several parts, to produce one uniform effect,
than a number of muscles do, in many of
the animal functions, and in many volun-
tary actions. Yet we see such actions no
less skilfully and regularly performed in
children, and in those who know not that
they have such muscles, than in the most
skilful anatomist and physiologist.

Who taught all the muscles that are
concerned in sucking, in swallowing our
food, in breathing, and in the several na-
tural expulsions, to act their part in such
regular order and exact measure ? It was
not custom surely. It was that same power-
ful and wise Being who made the fabric of
the human body, and fixed the laws by
which the mind operates upon every part

• The parallel movemr nt, like other reciprocities
of the two eyes, can be explained physiologically,
liy the mutual relation of their nerves, without re-
curring to any higher or more mysterious principle —

t This is not correct. Muscles which have cor.
relative motions are now either known or admitted
to have correlative ntrves — H.



of it, so that they may answer the pur-
poses intended by them. And when we
see, in so many other instances, a system
of unconnected muscles* conspiring so won-
derfully in their several functions, without
the aid of habit, it needs not be thought
strange, that the muscles of the eyes should,
without this aid, conspire to give that di-
rection to the eyes, without which they
could not answer their end.

We see a like conspiring action in the
muscles which contract the pupils of the
two eyes ; and in those muscles, whatever
they be, by which the conformation of the
eyes is varied according to the distance of

It ought, however, to be observed, that,
although it appears to be by natural in-
stinct that both eyes are always turned
the same way, there is still some latitude
left for custom.

What we have said of the parallel motion
of the eyes, is not to be understood so strictly
as if nature directed us to keep their axes
always precisely and mathematically par-
allel to each other. Indeed, although they
are always nearly parallel, they hardly ever
are exactly so. When we look at an ob-
ject, the axes of the eyes meet in that
object : and, therefore, make an angle, which
is always small, but will be greater or less,
according as the object is nearer or more
remote. Nature hath very wisely left us
the power of varying the parallelism of our
eyes a little, so that we can direct them to
the same point, whether remote or near.
This, no doubt, is learned by custom ; and
accordingly we see, that it is a long time
before children get this habit in perfection.

This power of varying the parallelism of
the eyes is naturally no more than is suffi-
cient for the purpose intended by it ; but
by much practice and straining, it may be
increased. Accordingly, we see, that some
have acquired the power of distorting their
eyes into unnatural directions, as others
have acquired the power of distorting their
bodies into unnatural postures.

Those who have lost the sight of an eye,
commonly lose whatthey had got by custom,
in the direction of their eyes, but retain
what they had by nature ; that is, although
their eyes turn and move .always together,
yet, when they look upon an object, the
blind eye will often have a very small devia-
tion from it ; which is not perceived by a
slight observer, but may be discerned by
one accustomed to make exact observations
in these matters.

* See the preceding note.

Section XI.


Another phenomenon which hath per-
plexed philosophers, is, our seeing objects
erect, when it is well known that their
images or pictures upon the tunica retina
of the eye are inverted.

The sagacious Kepler first made the
noble discovery, that distinct but inverted
pictures of visible objects are formed upon
the retina by the rays of light coming from
the object. The same great philosopher
demonstrated, from the principles of optics,
how these pictures are formed — to wit,
That the rays coming from any one point
of the object, and falling upon the various
parts of the pupil, are, by the cornea and
crystalline, refracted so as to meet again
in one point of the retina, and there paint
the colour of that point of the object from
which they come. As the rays from dif-
ferent points of the object cross each other
before they come to the retina, the picture
they form must be inverted ; the upper
part of the object being painted upon the
lower part of the retina., the right side of
the object upon the left of the retina, and
so of the other parts.*

This philosopher thought that we see
objects erect by means of these inverted
pictures, for this reason, that, as the rays
from different points of the object cross
each other before they fall upon the retina,
we conclude that the impulse which we feel
upon the lower part of the retina comes
from above, and that the impulse which
we feel upon the higher part comes from

Des Cartes afterwards gave the same
solution of this phenomenon, and illustrated
it by the judgment which we form of the
position of objects which we feel with our
arms crossed, or with two-sticks that cross
each other.

But we cannot acquiesce in this solution.
First, Because it supposes our seeing things

Online LibraryThomas ReidThe works of Thomas Reid, D.D.; now fully collected, with selections from his umpublished letters → online text (page 35 of 114)