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THE SENSES
AND
THE MIND.
_PHILADELPHIA_:
AMERICAN SUNDAY-SCHOOL UNION,
NO. 146 CHESTNUT STREET.
_LONDON:_
RELIGIOUS TRACT SOCIETY.
NOTE.--The _American Sunday-school Union_ have made an arrangement
with the _London Religious Tract Society_, to publish, concurrently
with them, such of their valuable works as are best suited to our
circulation. In making the selection, reference will be had to the
general utility of the volumes, and their sound moral tendency. They
will occupy a distinct place on our catalogue, and will constitute a
valuable addition to our stock of books for family and general reading.
As they will be, substantially, reprints of the London edition, the
credit of their general character will belong to our English brethren
and not to us; and we may add, that the republication of them, under
our joint imprint, involves us in no responsibility beyond that of a
judicious selection. We cheerfully avail ourselves of this arrangement
for giving wider influence and value to the labours of a sister
institution so catholic in its character and so efficient in its
operations as the _London Religious Tract Society_.
☞ The present volume is issued under the above arrangement.
CONTENTS.
Page
CHAPTER I. 5
ON THE GENERAL RELATIONSHIP OF MAN TO THE WORLD AROUND HIM,
AND HIS ADAPTATION TO THE PLANET HE TENANTS
CHAPTER II. 45
MAN'S KNOWLEDGE OF THE QUALITIES OF MATTER OBTAINED THROUGH
THE MEDIUM OF THE SENSES
CHAPTER III. 69
THE SENSES, AS THE INLETS TO KNOWLEDGE--SIGHT AND HEARING
CHAPTER IV. 153
OBSERVATIONS ON THE AGENCY OF THE SENSES, RELATIVE TO
THE UNION BETWEEN MIND AND MATTER; AND ON THE OCCASIONAL
IMPERFECTION OF THE BODILY ORGANS OF THE SENSES, WITH THE
RESULTS DEPENDING THEREUPON
THE SENSES AND THE MIND.
CHAPTER I.
ON THE GENERAL RELATIONSHIP OF MAN TO THE WORLD AROUND HIM, AND
HIS ADAPTATION TO THE PLANET HE TENANTS.
There are few, at least among the reflecting portion of society,
who have not either mentally or verbally asked the question: Is the
sun--is the moon--are the planets, with their satellites--are the
stars, those suns of other systems, tenanted, as is our planet, the
earth, by living beings, which declare the omnipotence of God? This
is one of many questions which cannot be answered. The probability,
to judge from analogy, is, that some, if not all, are inhabited;
that some are in a course of preparation for beings which God will,
in his own time, call into existence; and that in all, changes have
taken place more or less similar to those which have occurred on the
globe we tenant, and which have been connected with the extinction of
races, and the creation of others adapted and organized for an altered
condition of the earth's surface, and of the circumambient atmosphere.
But, granting these suppositions, it must be evident, that the living
beings in the sun, the planets, and the asteroids, must not only be
differently constructed from those which inhabit our planet, the earth;
but, also, that in different worlds, the living inhabitants must be
very diversely constituted, not only as regards their senses, but also
their organization and their powers of locomotion.
We cannot conceive of beings unlike ourselves, and the animals,
terrestrial and aquatic, which, called into existence by Almighty
Power, people the surface of our earth; that, however, is no reason
why such beings should not exist, for what is impossible with God?
Nay, as it is, the senses, the operations, the powers, and economy
of insects confound us, and lead us to suspect that they possess a
sense, or senses, which, because denied to us, we cannot appreciate. In
our world, atmospheric air, in which oxygen prevails, or water, also
oxygenated, is essential to the maintenance of animal life. But cannot
the Almighty construct organic beings, independent of our air or our
water--vitalized, in fact, on principles of which we can form no idea?
Undoubtedly. If, for example, no aquatic water-breathing animals, as
fishes, crustacea, etc., existed on our earth, could we conceive of the
possibility of their being? or, were our race, and all other animals
furnished with gills instead of lungs, and ordained to a sub-aquatic
life, making the wide ocean our home, could we form any idea of what
creatures could be constituted for living in the thin atmosphere, and
actively enjoying life under its pressure? Again, let the attractive
force of this earth be altered, the organization of every living thing
must (granting its existence to be guaranteed) be altered accordingly.
We take the following from Miss Somerville's "Connexion of the Physical
Sciences," p. 73:--"The densities of bodies are proportional to their
masses, divided by their volumes. Hence, if the sun and planets be
assumed to be spheres, their volumes will be as the cubes of their
diameters. Now, the apparent diameters of the sun and earth, at their
mean distance, are 1922″, 8, and 17″, 1552, and the mass of the earth
is the 354,936th part of that of the sun, taken as the unit. It
follows, therefore, that the earth is nearly four times as dense as
the sun; but the sun is so large that his attractive force would cause
bodies to fall through about 335 feet in 1″; consequently, if inhabited
by human beings, they would be unable to move, since their weight would
be thirty times as great as it is here." A man of moderate size would
weigh about two tons at the surface of the sun; whereas, at the surface
of the asteroids, (the clusters between Mars and Jupiter,) he would be
so light that he could not stand steadily, since he would only weigh a
few pounds.
The densities, that of water being 1, as far as can be satisfactorily
explained, are as follow:--Sun, 1-2/15; Mercury, 9-1/6; Venus,
5-11/15; Moon, 4-1/2; Mars, 3-2/7; Ceres, 2; Pallas, 2; Jupiter,
1-1/24; Saturn, 13/32; Herschel, 99/100.
Similar observations apply to the influence of the atmosphere, in
whatever point of view we consider it, that is, whether we regard its
weight, its electrical condition, its illumination, its temperature,
its dryness, or humidity.
1. _Its Weight._--The weight of the atmosphere (an elastic,
compressible, and expansible fluid,) is calculated to be from fourteen
to fifteen pounds avoirdupois on every square inch, (pure water,
taking bulk for bulk, being about 828 times as heavy.) Now, reckoning
the surface of a middle-sized man to be fourteen feet, he sustains
the pressure of eleven tons. Many of our readers have seen the
philosophical experiment of placing two hollow metallic hemispheres
rim to rim, the rims being nicely adjusted and smeared with lard;
this being done, the air, by means of a stop-cock on the lower
hemisphere, screwed into a powerful air-pump apparatus, is drawn out
or exhausted--the stop-cock is turned--the globe is unscrewed from the
air-pump, and placed in the hands of those who may consent to try their
strength in pulling the two hemispheres asunder. Enormous is the force
required; if the diameter of the circle be fourteen inches, the least
force that will separate them will be equivalent to half a ton.
Such, then, being the pressure of the atmosphere, as is clearly proved
by simple experiments, it may at first create some surprise that the
human body is capable of sustaining it without being crushed; that
the tiny insect, with its delicate wings--and in some these amount to
several square inches of surface--is not reduced to atoms. But the
wonder will cease, when we reflect that this pressure, or a pressure
little short of it, is essential to the existence, not of man only, but
of all terrestrial organic beings.
Dr. Robinson justly observes, that "the human body (he might have said
every organic body) is a bundle of solids mixed with fluids, and there
are few or no parts of it which are empty. All communicate either by
vessels or by pores, and the entire surface is a sieve, through which
the insensible perspiration is performed. The whole extended surface
of the lungs is open to the pressure of the atmosphere; everything,
therefore, is in equilibrio; and if free or speedy access be given
to every part, the body will not be damaged by the pressure, however
great, any more than a wet sponge would be deranged by pressing it to
any depth in the water."[1]
[1] Mechanical Philosophy, vol. iii. p. 54.
On this we would remark, that the human body, and that of terrestrial
animals in general, is not adapted for the pressure of water at great
depths; even could man by any contrivance breathe, such a pressure
would destroy life; and, indeed, few aquatic animals are constituted
for oceanic existence in the depths of the sea. While the surface is
alive with its myriads, the depths are still and untenanted; while
bays, shores, reefs, and sandbanks, covered by many fathoms of water,
are teeming with shelled mollusks, fishes, and thousands of wondrous
creeping things, the profundity of ocean is a comparative desert;
whatever lives there must be so constituted as to sustain a tremendous
amount of aqueous pressure. Indeed, whales, which often plunge to a
considerable depth, and remain submerged for twenty minutes, during
which time respiration is suspended, are provided by their coating of
blubber, and by the peculiar arrangement of their arterial and venous
systems, for the pressure they then undergo; but this pressure often
repeated, as it is when the animal is wounded and hard driven, soon
produces great exhaustion. Captain Scoresby, for example, harpooned a
whale, which, on receiving the weapon, descended four hundred fathoms,
at the rate of eight miles an hour; but these animals, when suffering
from the torture of the harpoon, often descend to a much greater depth,
and sometimes strike so violently against a hard bed of the ocean as
to fracture their jaws. At the depth of eight hundred fathoms, captain
Scoresby calculates the pressure at 211,200 tons. On the other hand,
the organization of man (and other animals) is as ill calculated for a
much lighter pressure than that of our atmosphere at sea-level, as it
is for great pressure in the depths of ocean.
In proportion as we ascend the alpine elevations of our globe, or
mount upwards in a balloon, we find the air more and more rarefied.
These elevations are, however, but trifling; nevertheless, trifling
as they are, what an effect the decrease of pressure produces on the
human frame! The heart beats with violence, the lungs gasp for more
air, they have not pressure enough; the blood begins to ooze out of the
minute vessels ramifying through the tissue of their delicate cells;
blood issues from the nose, the eyes, the ears; the slightest exertion
becomes oppressive--a mile or two higher, and death is inevitable. The
difficulties attendant upon the ascent of Mont Blanc, the vast Himalaya
chain, and the heights of the Cordilleras, are quite as much connected
with the state of the air as with the terrible ravines and precipices
which obstruct the way. Indeed, as is well known, on the elevated
plateaus of South America or Thibet, men and animals accustomed to
low plains, or even to gently undulating grounds, are for a long time
distressed for breath, and incapable of bodily exertion. Time alone
habituates them to the rarer and lighter atmosphere. But what is an
elevation of 13,000 or 14,000 feet, nay of 15,668 feet, (Mont Blanc,)
of 25,747 feet, or 28,077 feet, (Jewahir and Dhawalagiri, peaks of the
Himalaya,) to that of twenty or thirty miles? At an elevation of twenty
miles, the heart of a human being would burst, his lungs become gorged
with blood, from every pore of his body a sanguine stream would gush
forth--he would immediately die. Is not, then, the pressure of the
atmosphere necessary for the existence of man, constituted as he is for
the planet which he inhabits? But the atmosphere, with regard to its
relationship to the solid globe it environs, demands a few words.
This elastic fluid must be considered as a body of air revolving with
the earth, whence it must be evident that the velocity of the strata of
air, if we may use the word, increases as we recede from the earth's
axis; for example, at the equator, that stratum of air, (if such there
be,) which is twice as distant from the centre of the earth as the
surface is, must revolve with twice the actual velocity of the air at
the surface. Taking this fact into consideration, it results that,
however attenuated, however rarefied, the atmosphere cannot extend
beyond 20,000 miles from the surface of the earth; far above that
elevation the centrifugal force would counteract the centripetal,
or, in other words, the tendency of the particles to the earth would
cease, and, consequently, unless air pervaded the universe, which is
not the case, 20,000 miles are within the utmost range of possibility.
The fact, however, appears to be demonstrated, that the limits of our
atmosphere do not exceed an elevation of above forty-five or fifty
miles, and that beyond this there is no refraction or reflection of
the solar rays--that, in fact, air ceases. The finite extent of the
atmosphere has been ably discussed by Dr. Wollaston,[2] his arguments
being based upon the _Atomic Theory_ of matter. We may thus condense
his train of reasoning, as far as it bears more immediately upon the
present subject.--If air extend throughout the universe, we shall be
obliged to admit that every planet must collect an atmosphere around
itself proportionate to its attractive power. In this case, as he
argues, Jupiter, at whose surface the force of gravity must be much
greater than that of our earth, would certainly collect a large and
dense atmosphere around him. The effect of the refraction of light
through this atmosphere would become visible on the approach of the
satellites to the planet, when they disappear behind his disc, and
would cause a sensible retardation in their rate of approach. Now, it
is allowed that no such retardation, even in the minutest sensible
degree, can be observed, and hence it follows that Jupiter has no
such atmosphere as that of our earth, nor the means of collecting
it; consequently, air, such as that composing our atmosphere, is not
diffused in any degree of rarefaction through the solar system. This
finite character of our atmosphere is, as Dr. Wollaston contends,
more conformable to the atomic theory than to that of the infinite
divisibility of matter; since, in the first case, a boundary is
possible, and will exist at the point where the weight of a single atom
is as great as the repulsive force of the medium; while, in the latter
case, it is difficult to see the possibility of any boundary.
[2] Phil. Trans., 1822.
By way of note we would here add, that the theory of the _infinite_
divisibility of matter, which all the laws of chemistry seem to deny,
has no good grounds for our acceptance. God made matter, and, as we
may humbly conceive, in the form of ultimate atoms, which, however
inconceivably minute, must be definite--otherwise what is meant by
creation? That which is created must have definite figure, size, etc.,
else it is nothing; and to talk of a creation where size of figures
is absent, is absurd. We know that atheistical philosophers advocate
the theory of the infinite divisibility, and infinite, essentially
infinite duration of matter, for these points are steps to the theory
of non-creation, or rather involve it. Infinite duration, infinite
divisibility, infinite extension, and the plastic power of infinite
time, together with the innate, ungiven laws of this infinite matter,
form the key-stones to their unholy temple entrance. On this theory,
worlds formed themselves, and harmonized with each other; living
microscopic monads called themselves into being, and by voluntary
exertion became developed through various phases into man. Thus, then,
he owes no Creator thanks! Impious, irrational, debasing doctrine!
Supposing, then, that our atmosphere is not continued to an altitude
exceeding fifty miles, forming a sort of circumambient ocean, at
the bottom of which we live, and which is created for our peculiar
organization, still it is not altogether improbable that some subtle
ethereal fluid, altogether different from our atmosphere, may extend
itself throughout space--a fluid of extreme attenuation, the nature of
which is to us unknown in fact--a fluid so impalpable as to cause no
sensible retardation to the rate of motion in the planets.
We do not positively assert that such a subtle fluid exists, though
many astronomers are in favour of this hypothesis; and, indeed, we
believe that Encke's comet appears in successive revolutions to show
in some slight degree the effect of some medium resisting its motion,
and that the same observation applies to the comet of Biela. But when
we consider the great tenuity of the substance of these comets, through
which even faint stars may be seen, we shall be justified in regarding
this resisting medium as being more subtle, attenuated, and elastic,
than can be well expressed in words.
To revert now to our atmosphere, there is another interesting point
which requires our notice; namely, are the constituents of this
atmosphere chemically united together, or only simply mixed in certain
proportions? We believe that it consists of a simple mixture only of
two essential gases, or elements, namely, oxygen and nitrogen, with
a small and variable quantity of carbonic acid, and also with water
in a state of vapour. We may consider the last two as accidental
ingredients, essential as the vapour of the atmosphere may be to the
necessities of animals and plants, to luxuriance of scenery, and
fertility of soil. The essentials of air are united in the following
proportions, namely, one part of oxygen and two of nitrogen, or one
atom of oxygen and two atoms of nitrogen; but as the atomic weights
of oxygen are as 8 to 14, the proportion of the weights of the two in
any given quantity of air will be that of 8 to 28, or two to seven; in
other words, nine grains by weight of air will contain two grains of
oxygen, and seven of nitrogen, supposing the air to be pure.
But, as we have said, a portion of carbonic acid gas is usually
contained in air; this gas is exhaled from the earth, and collects in
certain localities, rendering the air more impure than it otherwise
would be; as a rule, however, the quantity of this gas in intermixture
with the air we breathe--its lower strata--varies from three to eight
parts out of a thousand in weight; in its pure state, it is immediately
destructive to animal life; but thus diluted is in this respect
innoxious, while to the vegetable kingdom it is necessary. With respect
to water in a state of viewless vapour, the quantum in any given weight
of air seldom exceeds 1-1/2 per cent.
Now if, as most philosophers of the present day seem to consider, there
is no chemical union of the gases constituting the atmosphere, it may
be supposed that, according to their respective weights, a partial
separation and subsidence of the heavier will take place, while the
lighter will chiefly compose the upper portion--thus, for example,
a stratum of nitrogen will surmount a stratum of mixed nitrogen and
oxygen, and this a stratum of mixed nitrogen, oxygen, and carbonic
acid. The following passage from the Penny Magazine will illustrate
this theory: "A law is found to prevail in the mixture of gases and
vapours, as universal as is that relative to their expansion arising
from temperature, namely, that two gases in a state of mixture exercise
no influence one upon the other, except communication of temperature,
but that each is disposed in exactly the same way as it would be if
the other were not present. Thus it is found, entirely contrary to
all previous notions, that no pressure of dry air upon water exerts
the least influence in preventing the formation of steam, which goes
on exactly as if the space above were a vacuum, and continues until
further evaporation is stopped by the pressure of the steam already
created. It is found that no pressure of one gas can confine another
in water; but that, supposing a bottle partly full of water, the gas
confined in the water will escape to the surface, and distribute itself
in precisely the same way as if the other gas were not present. By this
it is not meant that the action, commonly called mechanical, cannot
take place, or that a stream of hydrogen would not trouble the air;
but only that the permanent settlement of one gas is not affected in
any way by the presence of another, so long as no chemical action is
excited.
"From this principle, Mr. Dalton,[3] taking into consideration the
presumptions which exist against the chemical union of the ingredients
of the atmosphere, infers, that the atmosphere does not altogether
consist of the compound called air, but that the nitrogen atmosphere
is higher than the oxygen atmosphere. In fact, if there be no chemical
union, the above law of the mixture of gases requires us to allow that
each is an atmosphere independent of the other, and that the two are
most probably of unequal heights. From some considerations into which
we cannot here enter, Mr. Dalton thinks that the actual pressures
exerted by the oxygen and nitrogen are in the proportions of the
volumes occupied by them, that is, as one to four; and concludes that
the oxygen atmosphere extends to thirty-eight miles in height, that of
nitrogen to fifty-four miles, that of carbonic acid to ten miles, and
that of aqueous vapour to fifty miles. It must be observed, however,
that the state of the carbonic acid of the atmosphere is very variable;
that there is not the same quantity by night as by day, in moist
weather as in dry; and that the higher strata of the atmosphere contain
more of it than the lower, which may arise from a rapid absorption by
the earth.
"Against the hypothesis just described, it might, perhaps, be asserted,
that the air which Gay-Lussac brought down from a height of more than
four miles was not found to differ from that of the earth's surface in
the proportion of its oxygen to its nitrogen, which would be the case
if the oxygen atmosphere diminished in density more than in proportion
to the diminution of that of the nitrogen, or _vice versâ_."
[3] Phil. Trans., 1826.
Without attempting to settle the question as to whether the component
parts of the air are in a state of chemical union, or only in a state
of simple mixture, of this we are sure, that the air is essential to
the existence of all organic beings which live on the surface of our
planet, that is to animals and plants, though the relationship of each
to the air is diverse. The following comparison between the two great
groups of organic creation, which we copy from an admirable paper on
the Progress of Organic Chemistry in the "Companion to the Almanack,
1849," shows the respective relationships of animals and plants to the
elements around them, as well as their mutual balance and dependence:--
An Animal is an Apparatus A Vegetable is an Apparatus
of Combustion. of Reduction.
_Burns_ Carbon _Reduces_ Carbon
" Hydrogen " Hydrogen
" Ammonium. " Ammonium.
_Exhales_ Carbonic Acid _Fixes_ Carbonic Acid
" Water " Water
" Oxide of Ammonium " Oxide of Ammonium
" Nitrogen, or " Nitrogen, or
Azote. Azote.
_Consumes_ Oxygen _Produces_ Oxygen
" Proteine " Proteine
" Fats " Fats
" Starch " Starch
" Sugar " Sugar
" Gum. " Gum.
_Produces_ Heat _Absorbs_ Heat.
" Electricity. _Abstracts_ Electricity.
_Restores_ Its elements to _Derives_ Its elements
the air or from the air or
earth. from the earth.
_Transforms Organized_ matter _Transforms Mineral_ matter
into _mineral_ into _organic_
matter. matter.
Is not the wisdom of God here manifest?--The vegetable kingdom is made
auxiliary to the animal, and _vice versâ_.--Yet, how? by mysterious
changes, appropriations, productions, and consumptions, upon which
modern researches are from time to time throwing new light; or, in
other words, unfolding to us new revelations of the power and wisdom
of the Great Eternal, who has condescended to give us a _spiritual_
directory, a guide to our feet, and a lamp to our path, by means of
which we, who at best only see through a glass darkly, may be led
into that glorious world where there are no clouds--where there is no
night--where there is "no need of the sun, neither of the moon, to
shine in it: for the glory of God" doth "lighten it, and the Lamb is
the light thereof."
2. _Its Electrical Condition._--With the electrical changes in the
state of the atmosphere are connected various transitions from heat
to cold, dew, rain, hail, snow, clouds, winds, thunder-storms, auroræ
boreales, haloes, parhelia, etc. In this point of consideration the
atmosphere bears upon organic life. The solid globe itself may be
regarded as a vast electrical or galvanic apparatus, and all the vital
functions of animal bodies involve electric or galvanic phenomena.
Magnetism appears to be essentially identical with electricity;
both are most intimately connected with light and heat; and not
only electric sparks, but all the phenomena of electricity, can be
obtained from a common magnet. It is not here our purpose to enter
into a philosophical treatise on electricity and galvanism; a little
consideration, however, will lead us to infer that the general
diffusion of this subtle electric fluid, if the term fluid be at all
applicable, is essential to the maintenance of organic life, and that
electrical changes are perpetually taking place in organic bodies.
This fluid is derived from the earth, or its circumambient atmosphere,
and its currents obey definite laws, which have been elucidated by the
experiments of some of the most profound philosophers of modern times.
After what we have briefly said respecting the electric condition of
our globe, and the electrical phenomena which are involved in the
processes of the vital functions, to say nothing of electro-magnetism,
it must surely be apparent, that even as the air is in itself necessary
to our existence, so the diffusion of that subtle matter, now quick,
now slowly acting, now energetic, and now darting from the clouds
to the solid earth a vivid flash, creating a momentary light in
darkness--is equally essential; this is a point which, by the world at
large, is but slightly taken into consideration. Remove this subtle
element from the earth, and what would be the result? Perhaps the globe
would deviate from her course; perhaps an alteration in her polar axis
would take place. Perhaps--but why enter into such speculations? This
is certain--animal and vegetable life, as at present constituted, could
not exist: but all is ordered aright; the organization of matter,
and the senses of living beings, are involved in the presence of an
element, variable, it may be, in its phases, but mighty in its effects.
Here animals and plants play their part transversely, for each other's
benefit; animals produce electricity, by means of the vital operations
of their organization, and this produce, given to the earth and air,
is abstracted by plants. They antagonize each other, and the result is
harmony.
3. _Its Illumination._--Light is evolved by and during the combustion
of various bodies, as wood, coal, tallow, and spirits, or alcoholic
fluids; it is the result of electricity--that is, of the electric spark
or flash; it is evolved during many chemical experiments, and by the
attrition of two quartz pebbles. The percussion of flint and steel
produces luminous sparks; these sparks consisting, as the experiments
of Mr. R. Hook have proved, of minute ignited globules of iron, struck
off at the moment of percussion. These, and many other sources whence
light proceeds, need not here be detailed; our object is with that
general light, the light of day, which results from the influence of
the solar rays. For the reception of pictures on the retina by means
of the rays of light reflected from all things within the scope of
vision, the eyes of animals are especially constructed. To some animals
a dim twilight suffices, so far as regards their personal maintenance
and their enjoyment of life; to a few the little light, which even
in the darkest night is not absent, is all that is required for
their ordained habits and economy. In such instances, the retina is
exquisitely susceptible, and the iris dilates to admit the entrance
of every feeble ray reflected from the objects either of their search
or avoidance. Often have we seen the owl, when twilight has melted
into darkness, skimming over the fields, along the lane, and around
the barn, quartering the ground in search of mice or moles, which, had
they been at our feet, would to our eyes have been invisible. On the
other hand, they would have been nearly, if not quite invisible to
the owl in the full glare of sunshine. Yet, be it understood, light
is as essential to the night-bird as to men, or the giraffe of the
glowing wilds of Africa. We know not what _total darkness_ is, unless
perhaps we be walled up in a deep dungeon underground, to which light
is utterly denied access; such living tombs have been contrived by
the diabolical minds of tyrants, pagan and papistical. In the darkest
night, even our eyes dimly discern the "form of things obscure"--things
which, to a nocturnal animal, would be boldly conspicuous.
Light is a stimulus both to the animal and vegetable worlds. It is
when daylight breaks that "man goeth forth unto his work and to his
labour until the evening;" it is when light breaks that the feathered
songsters of the grove join in one chorus of--why may we not say
so?--instinct-urged thanksgiving. O man, gifted with reason! O man, the
heir of immortality! utter, then, thy song of praise, of gratitude,
that the light of another day is bestowed upon thee: and then be
diligent in all that God has called upon thee to perform, seeing that
"the night cometh, when no man can work."
Light is a stimulus, more or less grateful to every living creature.
Reader, have you ever wandered along the sea-shore, and explored the
masses of rock left uncovered when the tide is fully out; there,
adhering to the surface of the stone, in little ponds, mimic bays, may
be seen scores of sea-anemonies (_actinia_.) If the sky be bright,
there will they be, with their painted tentacles all expanded, animal
flowerets feeling the influence of light; but let the sky change, let
clouds obscure the day, and they retract their tentacles and shrink
into repose. These animals have no eyes, but yet they are sentient of
light. We mention these sea-anemonies merely by way of example; other
eyeless, and we may say, apparently nerveless creatures evidently enjoy
the influence of light, as the hydra, the medusa, and the polyps of
corals.
If light waken up some animals from their repose--if it rouse the cock,
and bid him sound his "clarion shrill," it warns others to retire to
their obscure dormitory, and slumber till twilight recalls them into
activity. The moth now flits abroad, and the bat and the fern-owl are
on the wing, giving chase to their insect prey. The hedgehog is all
alert, searching for slugs, worms, and various creeping things, which
revel in the dews of sunset. It is then, too, that the fierce prowlers
of the forest issue from their lair, eager for blood; but when "the sun
ariseth, they gather themselves together, and lay them down in their
dens."
Light is not only a stimulus to animals, in the sense above noticed; it
appears to be essential to health and vigour. Of this we are the less
aware, because, under ordinary circumstances, we are always subject
to its influence. Men have been confined for years in dark dungeons,
and have reappeared upon the stage of life, pallid, meagre, weak, and
emaciated beings, like breathing corpses; confinement, bad food, ill
ventilation, and mental agony, had no doubt done their work; but want
of light also had part in the sad devastation of the animal frame.
Look, for example, at those parts of our bodies which are usually
clothed, and compare the colour of the skin with that of the hands
and face; strip the arm bare--the skin is acted upon by atmospheric
air, but yet how much whiter than that of the hand, delicate as that
hand may be. It may be said that heat, that is, solar heat, produces
the difference. Partly so, no doubt, but not altogether. The face and
hands of the Esquimaux are darker than his chest; moreover, suppose a
severe and extensive cut happens, and that the wound thus inflicted
is bound up for weeks by adhesive plaster, what do we see on removal
of the straps and bandages?--a singular whiteness of the skin, the
result, as it appears to us, of the exclusion of light from the
covered portion. Plants, as all must have noticed, have their leaves
and flowers drawn towards the light, and become pallid when kept in
dark places. Thus, for example, some flowers open only when the sky is
clear, as the little pimpernel, the index of fair weather; others, as
the sunflower, turn to the sun in his course from east to west; the
eyes, or germinating stalk of the potato, though they shoot vigorously
in the dark, are blanched; so are the covered leaves of endive, and
the covered stalks of celery and sea-kale. Light is a chemical agent;
light, as the apothecary well knows, greatly impairs the activity of
the dried and powdered leaves of foxglove, and blanches castor oil.
Light, therefore, is found to effect both chemical combination and
chemical decomposition.
In nothing, perhaps, is the chemical agency of light more clearly
shown than in the photogenic drawings, which are the fac-simile
representations of objects delineated by the action of light on a thin
sensitive layer of ioduret of silver. The following is the mode of
preparing the plates for the reception of photogenic drawings, given
in the Penny Cyclopædia:--These drawings "are produced on plates of
copper, coated over with silver, which are found to answer better than
such as are entirely of the last-mentioned metal. After being washed
with a solution of nitric acid, the plate is put into a well-closed
box, where it is exposed to the action of iodine, a small quantity of
the latter being placed at the bottom of the box, with a thin gauze
between it and the plate. A layer of ioduret of silver is thus formed
on the surface of the plate, and manifests itself by the yellow hue
produced on the silver, which shows that the process of giving the
plate the sensitive coating on which the action of the light delineates
objects is completed. Thus prepared, the plate is placed within a
camera obscura, of particular construction, and the delineation of
the object is then effected in a very short space of time; but has to
be afterwards brought out and rendered distinct by another operation,
namely, submitting the plate to the action of vapour of mercury. Even
then the process is not completed, for the plate has to be plunged into
a solution of hyposulphate of soda, and afterwards washed in distilled
water, which being done, the impression is fixed, and the plate may be
exposed to light with perfect safety."[4] With reflection, refraction,
and polarization of light, we have here no concern; therefore,
interesting as the subjects are, we must pass them by.
[4] For further details, see the Handbook of Heliography,
London, 1840; and (for preparing-paper) the Visitor, 1839,
p. 290.
Light radiates from the sun with almost inconceivable velocity; that
is, at the rate of nearly 200,000 miles in a second. Hence it is about
eight minutes in traversing the intermediate space between our globe
and its starting point or origin. But here comes a question not easily
answerable. What is light? Is it matter? It is imponderable--can
we conceive of matter without weight? Again, whence does it derive
its velocity? The term radiation from the sun is convenient; but,
then, what is radiation? Is there light, (and is there heat,) above
the limits of our atmosphere? We cannot tell what the nature of the
mysterious emanation of light and heat from the sun is, nor whether
there are such phenomena as light and heat in empty space. Again, by
what process is this enormous manufactory of solar emanation kept up?
We may here lose ourselves in vague conjectures: He alone knows who
said, "Let there be light: and there was light."
The few details which we have thrown together, bearing upon the natural
light of our planet, derived from the sun, will suggest to the mind
of the Christian those apt comparisons, of the broad light of day to
the light of the gospel, transmitted to our souls from the Sun of
righteousness. Till illuminated from above, man wanders in spiritual
darkness; he sees neither the dangers that encompass him, nor the
road by which he should go; he may have the light of nature and the
light of science within him, but in spiritual affairs he is blind, and
will be chosen only by the blind as a leader. Let, however, the light
of revelation begin but to dawn upon him, and he learns to discover
more and more clearly his real position, his true character, and the
impossibility of his finding acceptance before God upon his own
merits. He feels himself to be a sinful creature, and is led to rest
upon the merits and atonement of the Son of God, who died for our sins,
and rose again for our justification. Thus enlightened, he receives
strength to pursue his journey to that bright and glorious kingdom of
which God himself is the Sun, and where there shall no more be night,
where "everlasting day abides," and all is glory and refulgence.
4. _Its Temperature._--Heat and light are distinct from each other,
though in many cases one accompanies the other, and is produced by the
same cause, as, for instance, by combustion, electricity, percussion,
the sudden condensation of air, etc. Heat without light, however, is
developed by the physical or chemical changes of bodies, as by the
condensation of steam, and the admixture of water with sulphuric acid.
It results, moreover, from the vital and mysterious operations which
are constantly taking place in organic beings, and especially in the
classes of mammalia and birds. But the great source of heat--that upon
which the temperature of our atmosphere mainly depends--is produced by
the influence of the solar rays.
There is, indeed, heat in the body of the globe itself; to say nothing
of volcanoes, we may state, that the deeper we penetrate into the
earth, the higher does its temperature become--a circumstance which
has led many philosophers to infer, that the centre of our globe is in
a state of incandescence. It is not here that we ought to moot this
theory, neither shall we enter into any speculations relative to the
intrinsic nature of heat; like light, it is a mysterious agent or
product, imponderable, yet subject to certain laws--laws which belong
to a branch of philosophy into which it is not now our province to
enter.
It may, however, be permitted us to state a few simple facts relative
to the atmospheric temperature of our globe, and the adaptation
of organic beings to the different degrees of heat within the
inter-tropics, in the temperate and in the polar latitudes. Climate
varies not only according to latitude, but also according to elevation,
the relative proportions of land and water, the nature of the surface
of the land, the extent of forests, etc. An island, for example,
like England, surrounded by the sea, destitute of mountains of vast
elevation, or of extensive morasses or forests, though lower in
atmospheric temperature during the summer months than the parallel
portions of the continent, has a milder atmospheric temperature during
winter. The cold of North America during winter is greater than in the
same parallels of latitude in the old world. Canada, for example, lies
parallel to the northern half of Spain and France, (between 40° and 50°
N. lat.) The severity of a Canadian winter is well known. At Quebec,
the summer is that of Paris, the winter that of St. Petersburg. At New
York, the summer is that of Rome, the winter that of Copenhagen. The
same observations apply to the eastern portions of Asia. At Pekin, the
scorching heat of summer is greater than at Cairo, while the winters
are as rigorous as at Upsal.
To the different climates of the globe certain plants and animals are
especially adapted; organic existence ranges from the poles to the
equator. How varied, how multitudinous, how wonderful, are the forms
and structures of organic creation, from the moss or lichen, which
creeps upon the surface of the rock, to the towering palm or gigantic
oak--from the microscopic animalcule or puny insect, to the ponderous
elephant or enormous whale! But, as we have said, every distinct region
has, in a general sense, its own _flora_ and its own _fauna_. It is
in tropical countries, beneath a fervid sun, that vegetation presents
us with its utmost magnificence. There we see forests of evergreen
trees, palms, and arborescent ferns--there bloom flowers of gorgeous
hue, and luscious scent--there ripen fruits of most exquisite flavour,
attractive both to the sight and the taste.
It is there, too, that the elephant, the hippopotamus, and the
rhinoceros, the largest of terrestrial quadrupeds, roam the plain, or
wander in the dense forest; there are the birds conspicuous for the
gorgeous splendour of their metallic colours, and the insects for their
singular forms, their lovely painting, or dazzling effulgence. Receding
from the inter-tropics, we find vegetation on a less magnificent scale;
the trees are for the most part deciduous, various species of corn
are cultivated, the meadows are clothed with grass, and the vine and
the olive flourish. Beautiful are the flowers, richly tinted are the
insects; some few birds are splendid, but there are no sun birds, no
humming birds, no birds of paradise. Receding further, we come to
the extreme limits of the vine, and pass from temperate to colder
latitudes, latitudes in which pines and firs form woods and forests,
in which a scanty flora greets a tardy sun, in which the animals are
covered with fur, increasing in thickness on the approach of winter.
Beyond this territory the arctic regions open upon us. Yet even here
vegetable and animal life meet us; but the species are few in number:
the reindeer, the leming, the white hare, the musk ox, the polar bear,
and arctic fox, are among the most remarkable. The birds are chiefly
piscivorous, and all are migratory, passing southwards on the approach
of winter. Coarse herbage, lichens, and mosses, vegetate during the
fleeting summer, and lie buried beneath the snow during the winter. Yet
are these animals and plants as well adapted for their dreary realms of
snow and ice, as are the animals and plants of the rich inter-tropics
for their luxuriant region. Take the elephant, the hippopotamus, the
bird of paradise, or the glittering boa constrictor to Greenland, and
they perish; take thither the graceful palm, palmetto, or pandanus, and
they cease even to struggle for life. On the contrary, transport the
polar bear and the reindeer to the torrid plains of the inter-tropics,
and their fate is sealed. The hardy plants, indeed, which endure the
arctic regions, are, in many instances, at least identical with those
that flourish in more temperate latitudes, but they are not to be found
in the low sultry plains of the inter-tropics. They constitute the
outskirts of northern vegetation.
The inter-tropical, the temperate, and the high northern regions of
the globe, are characterised, then, by their own _flora_ and _fauna_;
but there is a distribution of organic life exclusive of latitude,
which cannot but claim the attention of the naturalist. For example,
the marsupial animals are distributed between Australia and central
and southern America; but the American forms, very few in number,
are essentially distinct from those of Australia. Again, it is to
the warmer regions of the old world that the larger pachydermatous
animals are confined, such as several species of rhinoceros, the
hippopotamus, a tapir, two species of elephant, wild equine animals,
as the dziggetai, wild ass, quagga, zebra, etc., and various species
of wild hog. The living indigenous pachydermata of America consist of
two species of tapir, and two of peccary. On the contrary, America is
rich in the edentata, namely, sloths, ant-eaters, armadilloes, etc. The
pangolins, however, (_manis_,) are found only in the warmer parts of
the old world, and the aard-vark (_orycteropus_) is a native of South
Africa. We might enlarge greatly upon these observations, and extend
them to birds and reptiles, etc., were it our design to enter upon the
question; we shall only add, that in all regions animals are expressly
suited to the climate of the countries in which they respectively live;
they are constituted for the endurance either of heat or of cold, for
self-protection against all extremes of atmospheric temperature, and
for the enjoyment of existence, some under the equinoctial line, others
within the arctic circle.
The foregoing observations do not apply to the human race. Man was
ordained to replenish the earth; hence the pliability and energy of
his physical constitution, which enables him to endure the heat of the
inter-tropics, and the cold of Lapland or Nova Zembla--to dwell in the
deep valley or on the lofty mountain. When we say this, we look at
man as a species; we do not apply our remarks to individuals, or, in
other words, we do not assert that a Samoiede would enjoy the heat of
Ceylon or Sumatra, or that the Ceylonese would endure the rigours of
arctic Siberia; we only mean, that the fact of hot and cold climates
being inhabited by our race, proves that the physical condition of man
can accommodate itself to every extreme of natural temperature upon
our globe. It is true, that as a general rule man modifies his food,
his clothing, and even the nature of his habitation, according to the
temperature and products of the climate. The Laplander clothes his body
in warm furs, the Ceylonese in a scanty vesture of thin cotton. Yet the
wild Indians of some parts of North America, and the natives of the
dreary regions of Patagonia, are but loosely defended from the severity
of the cold, either as it respects dress or their huts. The Scottish
Highlander of the olden time, wrapped in his tartan, could sleep on
the heather of the mountain side during a bitter sleety night without
injury. After all, however, in the arctic regions the maintenance of
life is a struggle; the depressing influences of cold, cheerless skies,
and scanty food, tend to render the powers of the mind and the bodily
frame alike stunted and undeveloped. Nature here holds out the means of
life with a niggard hand, and it is from the sea principally that the
supply of food and other necessaries are obtained.
On the other hand, within the tropics the means of existence are
lavishly bestowed, the stimulus of animal food is not required, while
the earth yields its vegetable productions in abundance; but in these
regions, no strong motive stimulating to active exertion, the mental
powers become enfeebled, and all those vices inseparable from habitual
indolence are engendered. It is in the temperate regions, where nature
is not lavish, but liberal, and yet requires the hand of labour and the
head of thought, that the human race is presented to us in its highest
form, whether bodily or mentally considered. It is in such regions
that arts attain to perfection; that science walks hand in hand with
religion. A thousand necessities urge to exertion and enterprise, and
these are followed by a due reward.
Thus, then, are organic bodies, plants, the lower animals, and man,
affected by atmospheric temperature; but man has called in heat,
artificially produced, if we may use the word in a certain sense, to
his aid. Without heat, ore could not be smelted, or instruments of
metal made; glass and earthenware could not be manufactured; houses
could neither be built, nor furnished with articles of utility; the
operations of agriculture could not be successively carried on, nor
ships built, nor steam engines or machinery be constructed, nor could
man clothe himself or cook his food. In short, were it to please the
Almighty to suspend the laws of caloric, man would be rendered at
once helpless, and his senses useless; he must necessarily become a
completely altered being, granting even that his continuance as a
species upon the face of the earth were guaranteed.
With what wisdom, then, are the laws of the Almighty framed! How
happily do they all conjoin to fit this world for the exercise of our
senses and our reason! Yet, how mysterious they are! We know not even
what light and caloric really are; they are incomprehensible, and
yet we experience their influence, and daily test their laws. Who,
then, can wonder that the fall of man, the decrees of God, the advent
of Christ, his Divine and human nature conjoined, his death as an
atonement of inestimable value, his intercession for all who come to
him with faith, and the sanctification of the Holy Spirit, are each and
all mysteries? "Canst thou by searching find out God?" Yet the believer
knows _that_ God to be his Father and his Friend; he walks by faith and
not by sight, "by faith of Jesus Christ unto all and upon all them that
believe," and are "justified freely by his grace through the redemption
that is in Christ Jesus." When we reflect upon the mysteries of nature,
let us also think upon the mysteries of grace; let the consciousness of
our own ignorance lead us to throw aside presumption, and trust to the
words dictated by Him, to whom all mysteries are open, and whose wisdom
and goodness have no bounds.
5. _Its Dryness or Humidity._--Evaporation from the waters of the
globe, from seas lakes, rivers, etc., is perpetually taking place,
the ratio of evaporation being determined by the temperature of the
atmosphere; that is, it increases as the temperature increases. Hence
the actual quantity of water in a state of invisible vapour in the
atmosphere will be the greatest when the temperature of the latter
is the highest. Speaking according to our feelings, we then call the
air dry, although, in fact, the quantity of water in solution in the
atmosphere may balance the demands of the temperature.[5] But this
invisible vapour is liable from a thousand causes to condensation,
dependent upon one law, namely, that when a portion of air, saturated
with invisible vapour, is cooled below the point of saturation, a
portion of the vapour becomes condensed, according to the degree of
cold, so as to leave a due balance of vapour in the air, according to
its altered temperature. Who has not seen the window-panes of a heated
room in cold weather bedewed with trickling moisture? The vapour of the
room is in abundance, although invisible; but certain strata of the air
thus charged come in contact with the cold panes, and lose a portion of
their caloric, and with their caloric a portion of their vapour, (to
which, perhaps, the respiration of a large party has contributed,) and
this becomes condensed in the form of a visible fluid. If we breathe
against a cold pane of glass, we soon render it dim by moisture. On a
hot summer's day, we do not perceive the vapour of our breath; but on a
cold, clear, frosty day, a visible vapour or little mist is exhaled.
[5] The quantity of water in solution in the atmosphere
can never be greater than the quantity proper to the
temperature; but it may be less.
From electric changes, from currents of air, from sudden or gradual
depressions of atmospheric temperature--be the cause what it may--the
condensation of invisible vapour in the atmosphere is perpetually
taking place. But the extent and degree of condensation is very
variable. Sometimes, or rather very commonly, the quantity of water
separated is small, and condensed into such minute particles that
they float in the air, higher or lower, forming wreaths of mist,
or clouds of various patterns, density, and extent; sometimes they
appear at a great altitude, like silvery waves, or snowy fleeces;
sometimes at a lower altitude they take the shape of dense irregular
masses, presenting to fancy's eye the outline of monstrous animals, of
mountains, and castellated rocks; and sometimes the whole horizon is
beclouded and dark; we then know that the condensation is increasing.
What is the result? A fall of rain, snow, or hail, in which latter
case the water is not only condensed into its ordinary form, but into
pellets of ice. The water has passed through a stratum of air at the
freezing point. Sudden hail-storms in summer may, we think, be classed
among phenomena dependent on electric changes and operations in certain
atmospheric strata.
We have here, then, two processes--one of evaporation, another of
condensation; and these, by an express and admirable provision, have
a constant tendency to limit each other's operations. Evaporation is
increased by heat, but it produces cold in proportion to the rapidity
with which it is carried on. Condensation is produced by cold, and at
the same time heat is liberated.
How happens it that clouds and rain are formed in the higher regions
of the air, and not closely round about us? In consequence of certain
laws, the air incumbent on the earth's surface, especially in the
hotter latitudes, is always under the point of saturation, the air
being really dryer than it is at a great elevation. These laws
depend on the difference in the tension or elastic force of vapour
at different temperatures; this elasticity increases rapidly from
the temperature of 32° to 212°, the increase being in a geometrical
progression, while the increase of the temperature of the air from a
high altitude to the earth is in arithmetical progression. Now the air
of our mixed atmosphere is the ingredient which controls the whole
mixture. The result is, that the quantity of vapour present in a mixed
atmosphere will, at any successive diminution of height above the
surface of the earth, become successively less and less than that which
would be required to saturate the air. The consequences of this result
are most important, and are connected with our general well-being, and
the due exercise of some at least of our senses.
The following passage from Dr. Prout's Treatise is so pertinent,
that we beg leave to transcribe it: "Over the greater portion of the
earth, the air which, during the day at least, is warmed by contact
with the earth's surface, and thus becomes lighter, has a constant
tendency to rise into the higher atmosphere. Now if this air were
saturated with vapour, of course, whenever by rising it became mixed
with colder air, its vapour would be more or less condensed, and a
cloud would be formed. Hence, if we lived in such an atmosphere, we
should be always enveloped in a mist, through which the sun would
not be visible. But, by the benevolent arrangement we enjoy, this
consequence is so entirely prevented, that, unless under peculiar
circumstances, and always for beneficial purposes, the air at the
earth's surface is hardly ever saturated with moisture. The air which
has been warmed by contact with the earth can, therefore, rise from the
surface without any condensation of its moisture within the limits of
its point of saturation. Thus, at the equator, before the air reaches
the temperature of 61°, the presumed point of its saturation, it must
ascend to the height of 6,000 or 7,000 feet. At this height its vapour
will be condensed, and a cloud will be formed, which may either be
precipitated on the spot from which its constituent vapour had risen,
or may be transported by the currents of the atmosphere, similarly to
refresh a distant country, or may again be dissolved in the air; while,
under all these contingencies, the whole of the lower portion of the
atmosphere is exempt from mist, and continues perfectly transparent.
These operations are unceasing; moreover, the very clouds, by giving
out their latent heat, and shielding the earth's surface from the
direct influence of the sun, have a still further effect, and have a
constant tendency to modify their own formation and existence."
We might here enter largely into other points of high interest
connected with the science of meteorology, did the nature of our
subject allow it. We do not forget that it is upon the senses that
we have to write, and accordingly we can go no further here than
to show, in a brief and succinct manner, a few of the principal
arrangements instituted by Almighty wisdom and power, which render
our solid globe and its circumambient atmosphere the fitting abode
of such forms of organic life as we are acquainted with, and for
which, in fact, the world was created. To this world all the senses
of animals are expressly accommodated. If there were no air, there
could be no organs of hearing--granting the existence of living beings
without respiration. If there were no light, or the laws of light were
otherwise than what they are, our eyes would be useless. Were our lower
stratum of atmosphere always enveloped in a dense mist, obscuring the
rays of the sun, the sphere of our vision and its accuracy would be
greatly circumscribed--nay, sounds would fall more dully on our ears.
Suppose the globe closely shrouded by an oppressive fog; and then
imagine the condition of plants, animals, and man. Yet, did it please
our great Creator, it is in his power to call into existence plants and
animals fitted for so moist and obscure an atmosphere.
Again, the atmospheric temperature, the varying degrees of heat and
cold, according to latitude and to the characters of land--that is,
its elevation, its depression, the nature of its surface, and the
arrangement of adjacent seas, etc., are in harmony with the development
of life, and the due exercise of animal functions. Then, intimately
connected with this subject, are the laws of caloric, the suspension of
which would lead to the annihilation of all organic beings at present
constituted. Neither can we forget the weight of the atmosphere, its
varying electric conditions, nor the density and attractive force of
our planet. To these, and many other laws impressed upon matter, and
the results of those laws, are the physical organization of plants and
animals adapted, each in its own way, but yet with a mutual relative
bearing, conducive to universal order.
To the constitution of this earth are plants, living forms destitute of
feeling, hearing, sight, or indeed any sense known to us, adapted--yet
according to their kinds they know what nutriment to refuse or reject;
they are subject to the influence of temperature and of light and
darkness; some court the broad glare of the sun, others flourish only
in the shade. The same observations apply to certain of the lowest
forms of animal organization, which lead a vegetable life, and appear
not to be aware of their own existence. Nor, indeed, is it until we
ascend high in the scale of animal being, and arrive at a point at
which the senses are more or less developed, and in accordance with
this development, that of mind also, (for we can use no other term,)
that we discover a decided consciousness of existence, as manifested by
anger, fear, and other passions; by watchfulness, sensibility to pain
and pleasure of a mental kind; a recourse to artifice or to force as a
means of gaining certain ends; and other proofs of a something--call
it mind, or any other name--to which the senses appeal.
For, let us remember, it is only in a certain sense that the eye sees,
or the ear hears; in the former instance, nothing more than an image
of objects is inversely reflected on the retina, and yet the mind
recognises these objects in their proper position; and what is more,
not double, though the same object is figured on the retina of each
eye, or, in the case of insects, on the retina of scores of eyes. In
hearing, the minute auditory nerves merely receive an impulse from the
vibrations or wavelets of the elastic atmosphere, and this constitutes
what we call noise, tones, music, voice. But these tones or noises are
in the mind only; they are not appreciated by the exercise of any other
sense.
Having thus briefly endeavoured to show the harmony of the general
order of nature, as far as our globe and its animal and vegetable forms
are concerned, we shall proceed to the consideration of another portion
of our subject, and commence with it a fresh chapter.