tinguishes, that is, the manifold and various shades of
colours, on account of all bodies partaking of colour, and
thus by Sight, especially, we are able to perceive common
properties, such as form, magnitude, motion and number ;
but the Hearing, on the contrary, is perceptive only
of distinctions of sounds from sonorous bodies and the
variations of voice from such as have speech 2 . The sense
of " Hearing, however, contributes more than any other,
since speech is the channel for instruction, to the cultiva-
tion of the understanding."
Note 2, p. 93. All colour is motive of the diaphanous,
&c.] These passages seem almost to indicate a presenti-
ment of the modern or undulatory theory of light, for
they assume the existence of a diaphanous, that is, a
subtle medium which, by its motion, is creative of vision.
So too, the modern theory assumes a subtle elastic ethei*,
which has inertia without gravity, which fills space, per-
meates all bodies, and admits of being set in motion by
the agitation of the particles of ponderable matter, and
which particles, when set in motion, communicating a like
1 De Sensu et Sen*. \. 10. 2 I. n.
268 NOTES." [BK. u.
motion to the molecules adjacent, act upon others, and
thus motion is propagated further and further in all
directions. The theory of Aristotle is much the same
there is a diaphanous medium which may well represent
the subtle ether, and which, when potential, that is
quiescent, is darkness, and when set in motion by colour,
(the property of which is to render it motive), is light,
renders objects visible, that is. Thus, the same diaphaneity
when passive, that is, potential, is darkness, when active,
that is, in reality, is light, and the cause of objects being
visible. The value of the hypothesis is diminished by
the identification of the " diaphaneity" with air and water
and solid bodies, because of their affinity with the
supernal region or firmament above, which, together with
all the heavenly bodies, was supposed to be of igneous 1
nature ; and to be corporeal, circular, and in constant
motion.
Note 3, p. 94. LigJit is the active state, &c.] The
diaphaneity which, when passive, is darkness, when set in
motion and made active, is light, is made visible, that is ;
and thus light, being a mere condition of the diaphaneity,
"is not a body, for, were it so, there would be two bodies
in one, which is an impossibility." It may now seem
strange that Aristotle should have paid so little attention
to the opinion of Empedocles*, " that light arrives midway
from the sun, before it reaches the sight, or the earth ;"
for although it differed from his own, in regarding the sun
1 Meteoroloffica, 3. i. 2 De Ccdo, ?. 3.
CH. VII.] NOTES. 269
as the source of light and the distinction of day from
night, yet, in transmitted light, it supplied a motor,
which was required for the completion of his own theory
of sensation through the agency of a medium acted upon
by impulsion.
Note 4, p. 95. Now that which is without colour, &c.]
The diaphaneity, that is, when passive, is receptive of
colour and made active, just as the air, when quite still,
is more readily set in motion and made sonorous by per-
cussion ; and this leads, amid some confusion of thought,
to the consideration of those luminous appearances (ignes
fatui) which are visible only in the dark, by their colour.
'The precise nature of these appearances is still only
conjectural, notwithstanding the advance of chymistry ;
but they are supposed to be due to phosphyretted
hydrogen eliminated, under favouring circumstances, from
decaying animal and vegetable matter, and ignited by
contact with the atmosphere."
Note 5, p. 95. Therefore, witliout light colour is not
visible.] Colour, that is, by imparting motion to the
diaphaneity, renders it, from being potential and dark,
actual and visible, that is, light ; and thus, as without
light there is no colour, so without colour there is no
light ; and this lends support to the opinion, that the air,
as being a diaphanous medium, is essential to sight.
Aristotle had indeed maintained, in opposition to
Empedocles 1 and others, that vision is not caused by the
1 De Sensu et Sens. II. 15, 16.
NOTES. [BK. n.
emanation of luminous rays from the eye as light proceeds
from a torch or lamp ; and he ridiculed the notion that
vision is precluded in the dark owing to the extinction of
those rays therein. It is probable that this theory first
led him to adopt a medium and its successive motion, as
the immediate cause of vision ; as he had accounted for
hearing by the propagation of the impulse given to the
air by the sonorous body. Aristotle was unacquainted
with the structure of the eye ; but he was aware, of
course, that it contains humours, and these he held to be
necessary, not as being aqueous that is elementary but,
as being diaphanous, for this property seemed to be as
requisite for vision within the eye, as it is for the trans-
mission of light to the eye. It was this assumed succes-
sion of action, after impression upon a diaphanous medium,
which led to the conclusion that the eye itself must be
diaphanous, and, therefore, that the visual power must be
somewhere on the inside of the eye ; and this is the only
approximation to a right knowledge of the retina and its
relations.
Note 6, p. 96. It has thus then been said, <fcc.] The
cause of colour being visible is sufficiently obvious from
what has been said ; but fire was said to be visible both
in darkness and in light, owing to its being, as fire, of
the nature of the firmament above, which was believed
to be fire, or something identical with fire. It may be
presumed that the subject was here introduced, in order
to notice and account for those luminous appearances,
CH. VII.] NOTES. 271
which have been alluded to, and which, in that age, could
not but have been topics of wonder and speculation ;
they were irreconcilable besides, with the prevailing
notions of colour and light.
Note 7, p. 96. The air is the medium for sounds, &c.]
The air was by Aristotle held to be essential to sound ;
but it is not apparent why odour was supposed to be
transmitted by some modified condition of air or water,
unless, indeed, it was required in order to account for the
perception of odours by fishes and aquatic animals.
There was a difficulty, in fact, in accounting for the
transmission of odour through air and water, because
odour 1 was held to be a vaporous exhalation eliminated
by fire ; and the " special organ of smell was said to be
located about the brain*" the coldest of all parts of the
body, in order that the exhalation might there be con-
densed and made productive of smell. Thus, it might
seem to be irreconcilable with odour, that it should be
transmissible in air or water, and this may have led to
the hypothesis of a modified condition of the elements
for smell.
Note 8, p. 97. But neitfter man nor animals which
breatJte, &c.] The term in the text (avairvet), like our
own term breathing, is expressive both of inspiration
and expiration, whereas it is evident that the sense of
the passage requires the former process only. And yet
1 De Sensu et Sens. II. 19, 20.
2 De Part. Animalm, u. 7.
272 NOTES. [BK. n.
elsewhere l , Aristotle, in his criticism of the theory adopted
by Diogenes and Anaxagoras to account for the respira-
tion of fishes, has clearly distinguished the one from the
other. He objected also to Timseus and some others who
had maintained that expiration must precede the other.
Enough, however, that he perceived, although unac-
quainted with the parts on which odours impinge, or the
organ by which they are made sensible, that they could
gain access to the sense only through inspiration.
CHAPTER VIII.
Note 1, p. 100. Sound of the actual kind is tJie, &c.]
As sound is the result of percussion, the passage implies
something to be percussed, as well as something in which
that which percusses is to move ; but what that some-
thing is in which percussion is to be made is not explained.
Some commentators, as Simplicius, have considered the
words ev TIVI to imply, " the air which is interposed
between the sonorous body and the sense," and which,
but for the contradictory opinions of that age with
respect to the air, might be at once accepted as its
meaning ; and even taken as some special medium, as has
been suggested, it still may signify a, body of air. We
1 De Respiraticme, 2. 3.
CH. VIII.] NOTES. 273
may consider the voice, Plato 1 observes, as percussion
(sound, that is,) transmitted, by the air, through the ears,
brain and blood, to the sentient principle. But as the
nature and properties of the air were then, from the
want of experimental science, unknown, they were avail-
able for any hypothesis ; and yet there is evidence that
Aristotle, not to add Plato, did regard the air as essential
to sound and voice. Aristotle 2 , while agreeing with most
philosophers in ranking air among the four elements, "sees
a difficulty in determining what its nature may be in the
universe around the earth, or what its order in relation to
the other elements of bodies." He was aware of the air
holding water in solution, and observes that, whether
water be or be not produced, equally, from the whole air,
that which is around the earth must be not air only but
vapour, which is again to be condensed and become
water. Thus, " we maintain," he adds, " that fire and air,
water and earth are producible out of one another, and
that each of them is present, in potentiality, in each of
the others ; as is the case with all bodies, which have
a base into which each of them is ultimately reducible."
He has distinguished the air we inspire from that which
we send forth (eWe'jUTeii/) and to which he has given a
specific appellation (TO irvev^a) ; but owing to the diffi-
culty of determining either its nature or its office,
(although it is the subject of a special 3 treatise,) no
1 Timceus, 67 B. a Meteorologica, I. 3. 3. i.
3 irepl Trvev/j.a.Tos.
IS
274 NOTES. [BK. n.
unexceptionable equivalent for it can be offered. These
quotations shew, amid many suggestive observations, that
knowledge concerning the air was then very unsettled ;
and yet they prove, it may be assumed, that air was
implied in the passage referred to.
Note 2, p. 101. An eclw is produced w/tenever, &c."j
This passage is obscure, both from its elliptical wording
and the want of adequate exemplification ; but, in
attributing to the air elasticity and capability of being
reflected, it seems to suggest that the atmosphere only is
the cause of sound and, therefore, of echoes. So, accord-
ing to modern science 1 , "an echo is sound reflected from
a distant surface and repeated to the ear ; although
several other conditions are required for its production."
In another treatise 2 , it is assumed that reflexion of the air
(/' araicA.atrtt) is the immediate cause of an echo; and
since an echo is reflexion, "must there not be, for its
production, air confined, impacted and communicating, as
one mass, with that which is to be reflected?" But an
echo, whether or not audible, ought, as the text states,
looking at the properties of the air, to be a constant
occurrence ; for as light is continually reflected from
bodies, and thereby casting shadows by which light
is distinguished, so sound, owing to the air's elasticity,
must be often reflected and, therefore, repeated, in varying
degrees of intensity, according to the nature of the surface
on which it may have impinged. That age, in fine, wa.s
1 Brande's Hist, of Science. a Problemota, XI. 8.
CH. VIII.] NOTES. 275
acquainted with several of the properties of the air, but,
as they had not been tested experimentally, its acquaint-
ance with them was but conjectural, and could lead to no
positive inference ; it was reserved for modern science to
ascertain what the air is, and what its properties in rela-
tion to the world, its productions and inhabitants.
Note 3, p. 101. A void is rightly said, &c.] It would
be difficult even to conjecture what could have been
meant by a void in that age ; for although it had been
perceived 1 , it may be but obscurely, that the air rises by
fire (heat) to the upper regions and becomes ether, (as in
the Timceus, expiration is accounted for by the rising up
from within of the heated breath,) yet it is not to be
supposed that rarefaction was an admitted property of
the air, or that any condition like rarefaction was implied
in the void. Aristotle* observes, upon this topic, that,
"according to some philosophers, a plenum is a space or
vessel when full, and a vacuum or void is the same when
empty, thus making, as he says, the plenum to be identical
with the vacuum and space, excepting in conditions of
relation." In all this it is evident that no account was taken
of the air ; and he objects to Anaxagoras, (who had shewn,
experimentally, that the air is substance of some kind,) that
he argues against what had never been contended for the
advocates for a void maintain, he says, that it is a space
in which there is no tangible body, and, holding every
1 Meteoroloyica, II. i.
8 Xat. AutcuU. iv. 6. I.
182
276 NOTES. [BK. n.
thing to be corporeal, they consider that only to be a void
in which there is absolutely nothing ; so that it can be to
no purpose to shew that the air is something. This
epitome shews sufficiently how widely apart from one
another are the antient and modern significations of a
void, since it now implies such a rarefaction of the air as
can be obtained through the air-pump; and, as rarefaction
cannot be carried beyond 300 times, no proof can be
afforded of the possible existence of a void. Aristotle 1
objects to those who maintained that the void is identical
with any space filled with air, " for, if the air be driven
out, the space will clearly, he observes, be a void, in a
stricter sense than it was, since it will no longer be full
of air." But it would be foreign to the purport of these
notes to inquire further into the opinions of that age ;
it may be inferred, however, from what has been adduced,
that Aristotle, although he refused corporeity to the air,
was not a very consistent supporter either of the plenum
or vacuum.
Note 4, p. 102. Every sonorous body, <kc.] This
passage is a summary of all that physiology has now to
offer upon sound and hearing ; but although it might
have been surmised that sound is vibration of the air,
caused by a sonorous body and conveyed, by successive
undulations, to the organ of hearing, yet, as the internal
ear was then unknown, it is a surprising assumption that
air must be contained within the organ, in order that the
1 Topica, vn. i. ii.
CH. VIII.] NOTES. 277
vibration may be communicated to the sense. Aristotle
may perhaps have been led, notwithstanding the unstable
opinions of his age upon the air, to conclude that, as
sound " is present in the air," air must be connected with
the hearing, and, if so, be contained, naturally, within its
organ. The succeeding passages hardly admit of comment,
on account of their evident want of anatomical know-
ledge ; but they prove that the tympanic membrane had
been made out, as also that it may be so injured, as to
admit fluid from without into the ear. And this disease
of the membrane is aptly compared to ulceration and
consequent opacity of the eye's membrane, (the cornea,)
whereby the rays of light are precluded from entering
the eye and producing vision.
Note 5, p. 102. But proof is afforded, &c.] This
somewhat puerile experiment is still extant. It seems
strange that the very obvious cause of this phenomenon
did not occur to one who had surmised, without ana-
tomical proof, that there is air within the tympanum ; it
had escaped Aristotle, besides, that, in a former passage,
he had made the air which is immured vnthin the ear to
be immovable.
Note 6, p. 104. The voice is a sound, <fec.] This
passage is a clear definition of the voice, and it points,
although indistinctly, to the parts and functions concerned
in its formation. The voice ' is said to be different from
sound, and speech to be different from either; and, as
1 Hist. Animalm, iv. 9. r.
278 NOTES. [BK. n.
speech can be produced by no other part than the pharynx,
those creatures only can speak which have lungs, as speech
is the articulation of the voice by the tongue. Where-
fore, the voice and larynx send forth vowels, the tongue
and lips consonants, and these together make up speech.
So, too l , Cuvier says, that " man alone among animals can
articulate sounds, owing probably to the form of his
mouth and the mobility of his lips." The 2 pharynx, so
called, and trachea, are of cai*tilaginous nature, and this
because they are for the sake of the voice as well as
breathing ; and it is necessary that that, which is to give
out sound, should have firmness as well as smoothness.
But the larynx and pharynx are here alluded to as if
they were one and the same organ, and it may be, that
owing to the complicity of the parts and their multiplied
relations to one another, they were then so considered ;
but yet passages 3 might be cited, which seem to shew that
they were known, both by function and position, to
be different organs.
Note 7, p. 105. Nature employs, simultaneously, the air,
&c.] It was assumed by the physiologists of that and,
indeed, many subsequent ages, that the office of respira-
tion is merely to cool the blood, or rather to temper its
heat, which was supposed to be constantly tending to an
excess incompatible with life. In modern times, on the
1 Anatomic Comp. t. I. 15.
8 De Part, Animalm, vn. 3. 5.
3 Ibid. ii. 3. 9 ; in. 3. i.
CH. VIII.] NOTES. 279
contrary, the action of the air which is inspired upon the
venous blood has been by some regarded as a process of
combustion, and the source, through combustion, of the
special temperature which characterises all organised and
living bodies. Respiration is said, by Grant 1 , to be
essential to the constitution of animal bodies ; for by this
function " the vital fluids are purified and replenished, the
muscular system is furnished with its capability of action,
and the high temperature of the mammalia is preserved
in every condition of the surrounding element."
Note 8, p. 106. As proof of which we are, unable, <fec.]
The meaning of this passage, owing in part to the
unsettled knowledge of that age, is by no means evident ;
but it can be readily admitted, that the act of holding
the breath must set in motion, disturb, that is, the air
which has been inspired, and produce coughing rather
than articulation. The French commentator makes the
text (mvet xai TOVTO) to imply " disturbance of the
function;" Trendelenburg, however, sanctions the version
here given. It will be apparent, from what has been
adduced, that the word pharynx (of fishes) should have
been larynx, for this, being the upper part of the trachea,
is the tube which conveys air to the lungs, as the other,
being the upper part of the cesophagus, is the tube
which conveys food to the stomach ; and all fishes have a
pharynx, of course, but, as they do not breathe, they are
without a larynx.
1 Outlines, p. 592.
280 NOTES. [BK. u.
CHAPTER IX.
Note 1, p. 109. And there seems to be an analogy,
<fec.] Aristotle \ in thus making Touch superior to, and
more influential than any other sense, (for it is the most
perfect, he observes, of man's senses, although with respect
to some others he is inferior to many animals,) is sup-
ported by Cuvier 2 , who says, "that Touch is the most
important of all the senses, and that its several degrees of
perfection exercise a surprising influence over the nature
of different animals ; and that of all the vertebrata man
has the most perfect Touch." It is difficult to attach a
sense to the term hard or soft applied to flesh, which,
by anatomical 3 description, corresponds with the muscular
substance of the body ; but man is said to have softer
flesh than any animal 4 , and on this account, through the
delicacy of his sense of Touch, to be of all creatures the
most intelligent. It is presumable that Aristotle was led
to suppose, from this sense being spread, so to say, like
the muscular substance, over the surface of the body, that
its organ lies somewhere in or beneath the flesh, and thus
to have concluded that a relative hardness or density of
that substance, by impeding tangible impressions, may be
1 Hist. Animalm, I. 15. 14. * Anat. Comp. t. ni. 569.
3 Hist. Animalm, in. 16. r. 4 De Part. n. 16. 16.
CH. IX.] NOTES. 2S1
the cause of, or concomitant with dulness of the faculties.
The nervous system was then unknown, and Aristotle, so
fond of analogies, might readily suppose that the Touch
had, like other senses, its appointed organism ; and, if
there were such an organ, that it is extended over the
body, and thus must be in or beneath the flesh. The
Taste, as being a modification of Touch, was said to be
more delicate in man than animals.
Note 2, p. 110. There is a close analogy^ A similar
observation is made in the following chapter, and, besides
bringing sentient perceptions under some general law, it
was, probably, intended to shew that colour, sound, and
odour, although inappreciable by our senses, may still be
present. It shews, in fact, that our senses, being limited
in their capacity of perception, are not to be relied upon
when impressions are very greatly in excess or propor-
tionally faint.
Note 3, p. 111. Tlie smell is perceptive.] "That fishes
smell," Aristotle 1 observes, "is shewn in their being taken
by baits which have the particular odour, foul or grateful,
to which they are attached." But modern science has, of
course, determined both the seat and the structure of the
olfactory organ in fishes ; and shewn " how it is protected
from the violent and incessant action of the currents of
water required for respiration." Sanguineous* creatures
are all such as have red blood, and insanguineous, those
which, in place of red blood, have a pale bluish fluid
1 Hist. Animalm, TV. 8. 19. J Ibid. I. 4. 3.
NOTES. [BK. n.
circulating in their veins. These last include "insects,
molluscs, Crustacea, and creatures with more than four
Note 4, pi 111. And htnce Ae dijflmlty of detcr-
iMjy, ic.] If the site amd structure of the olfactory
sense, in the lower forms of life, are still somewhat con-
jectural, it may well be supposed that the smell in non-
breathing animals was, in that age, although seen to be a
feet, inexplicable. But yet, although anatomy could not
then determine the seat of the sense, it might have been
conjectured that, as such creatures are obviously affected
by odours, there must be some other inlet for them than
that through which impression is made upon animals ;
and the detection of this mode of perception, would have
been another instance of homologous physiology. Aris-
totle 1 , following Plato, placed the seat of the smell and
other senses in the neighbourhood of the heart ; but
" the organ was said to be located, suitably, between the
eyes."
Note 5, p. 1 12. Tke olfactory organ in man, appear*
to differ, <fcc.] The analogy is obviously faulty, as it
seems to imply that the olfactory, like the respiratory
organs, are furnished with a cover, by the raising of which
odours gain access to the sense ; or rather, owing to the
intricacy of the parts and imperfect anatomical know-
ledge, the epiglottis has been associated with the velum
and posterior fauces. It could answer no purpose, then,
1 De Part. Animalm, n. 30. 9. 17.
CH. IX.] NOTES. 283
to inquire, as some have, what animals have an operculum
for the smell, of that kind ? or what mean those veins
and pores? As although the operculum, that is, the
epiglottis, was known to be protective of the larynx and,
therefore, the respiratory organs, the relations of the
larynx with the parts associated with it had not been
made out ; and the veins and pores refer, probably, to the
bronchi and vessels within the chest.
Note 6, p. 112. In fine, odour is derived, <fec.] Aris-
totle here differs from Plato, who held that odorous
particles are in a state rather of fluidity ; and Cuvier '
says, that " the organ of smell is moistened with abundant
viscosity, which arrests the odorous particles contained in
air or water ; as fishes are sensible of odours. But odour,
being regarded as exhalation, was assumed to be of fiery
nature and, therefore, like the element, dry, and this
required, for the conformity of the hypothesis of like