THE RHYTHM OF MOTION.
§ 93. When the pennant of a vessel lying becalmed first shows the coming
breeze, it does so by gentle undulations that travel from its fixed to
its free end. Presently the sails begin to flap; and their blows against
the mast increase in rapidity as the breeze rises. Even when, being
fully bellied out, they are in great part steadied by the strain of the
yards and cordage, their free edges tremble with each stronger gust. And
should there come a gale, the jar that is felt on laying hold of the
shrouds shows that the rigging vibrates; while the rush and whistle of
the wind prove that in it, also, rapid undulations are generated. Ashore
the conflict between the current of air and the things it meets results
in a like rhythmical action. The leaves all shiver in the blast; each
branch oscillates; and every exposed tree sways to and fro. The blades
of grass and dried bents in the meadows, and still better the stalks in
the neighbouring corn-fields, exhibit the same rising and falling
movement. Nor do the more stable objects fail to do the like, though in
a less manifest fashion; as witness the shudder that may be felt
throughout a house during the paroxysms of a violent storm.
Streams of water produce in opposing objects the same general
effects as do streams of air. Submerged weeds growing in the middle of a
brook, undulate from end to end. Branches brought down by the last
flood, and left entangled at the bottom where the current is rapid, are
thrown into a state of up and down movement that is slow or quick in
proportion as they are large or small; and where, as in great rivers
like the Mississippi, whole trees are thus held, the name “sawyers,” by
which they are locally known, sufficiently describes the rhythm produced
in them. Note again the effect of the antagonism between the current and
its channel. In shallow places, where the action of the bottom on the
water flowing over it is visible, we see a ripple produced—a series of
undulations. And if we study the action and re-action going on between
the moving fluid and its banks, we still find the principle illustrated,
though in a different way. For in every rivulet, as in the mapped-out
course of every great river, the bends of the stream from side to side
throughout its tortuous course constitute a lateral undulation—an
undulation so inevitable that even an artificially straightened channel
is eventually changed into a serpentine one. Analogous phenomena may be
observed where the water is stationary and the solid matter moving. A
stick drawn laterally through the water with much force, proves by the
throb which it communicates to the hand that it is in a state of
vibration. Even where the moving body is massive, it only requires that
great force should be applied to get a sensible effect of like kind:
instance the screw of a screw-steamer, which instead of a smooth
rotation falls into a rapid rhythm that sends a tremor through the whole
vessel. The sound which results when a bow is drawn over a
violin-string, shows us vibrations produced by the movement of a solid
over a solid. In lathes and planing machines, the attempt to take off a
thick shaving causes a violent jar of the whole apparatus, and the
production of a series of waves on the iron or wood that is cut. Every
boy in scraping his slate-pencil finds it scarcely possible to help
making a ridged surface. If you roll a ball along the ground or over the
ice, there is always more or less up and down movement—a movement that
is visible while the velocity is considerable, but becomes too small and
rapid to be seen by the unaided eye as the velocity diminishes. However
smooth the rails, and however perfectly built the carriages, a
railway-train inevitably gets into oscillations, both lateral and
vertical. Even where moving matter is suddenly arrested by collision,
the law is still illustrated; for both the body striking and the body
struck are made to tremble; and trembling is rhythmical movement. Little
as we habitually observe it, it is yet certain that the impulses our
actions impress from moment to moment on surrounding objects, are
propagated through them in vibrations. It needs but to look through a
telescope of high power, to be convinced that each pulsation of the
heart gives a jar to the whole room. If we pass to motions of
another order—those namely which take place in the etherial medium—we
still find the same thing. Every fresh discovery confirms the hypothesis
that light consists of undulations. The rays of heat, too, are now found
to have a like fundamental nature; their undulations differing from
those of light only in their comparative length. Nor do the movements of
electricity fail to furnish us with an illustration; though one of a
different order. The northern aurora may often be observed to pulsate
with waves of greater brightness; and the electric discharge through a
vacuum shows us by its stratified appearance that the current is not
uniform, but comes in gushes of greater and lesser intensity.
Should it be said that at any rate there are some motions, as
those of projectiles, which are not rhythmical, the reply is, that the
exception is apparent only; and that these motions would be rhythmical
if they were not interrupted. It is common to assert that the trajectory
of a cannon ball is a parabola; and it is true that (omitting
atmospheric resistance) the curve described differs so slightly from a
parabola that it may practically be regarded as one. But, strictly
speaking, it is a portion of an extremely eccentric ellipse, having the
Earth’s centre of gravity for its remoter focus; and but for its arrest
by the substance of the Earth, the cannon ball would travel round that
focus and return to the point whence it started; again to repeat this
slow rhythm. Indeed, while seeming at first sight to do the reverse, the
discharge of a cannon furnishes one of the best illustrations of the
principle enunciated. The explosion produces violent undulations in the
surrounding air. The whizz of the shot, as it flies towards its mark, is
due to another series of atmospheric undulations. And the movement to
and from the Earth’s centre, which the cannon ball is beginning to
perform, being checked by solid matter, is transformed into a rhythm of
another order; namely, the vibration which the blow sends through
neighbouring bodies.[15]
Rhythm is very generally not simple but compound. There are usually at
work various forces, causing undulations differing in rapidity; and
hence it continually happens that besides the primary rhythms there are
secondary rhythms, produced by the periodic coincidence and antagonism
of the primary ones. Double, triple, and even quadruple rhythms, are
thus generated. One of the simplest instances is afforded by what in
acoustics are known as “beats:” recurring intervals of sound and silence
which are perceived when two notes of nearly the same pitch are struck
together; and which are due to the alternate correspondence and
antagonism of the atmospheric waves. In like manner the various
phenomena due to what is called interference of light, severally result
from the periodic agreement and disagreement of etherial
undulations—undulations which, by alternately intensifying and
neutralizing each other, produce intervals of increased and diminished
light. On the sea-shore may be noted sundry instances of compound
rhythm. We have that of the tides, in which the daily rise and fall
undergoes a fortnightly increase and decrease, due to the alternate
coincidence and antagonism of the solar and lunar attractions. We have
again that which is perpetually furnished by the surface of the sea:
every large wave bearing smaller ones on its sides, and these still
smaller ones; with the result that each flake of foam, along with the
portion of water bearing it, undergoes minor ascents and descents of
several orders while it is being raised and lowered by the greater
billows. A quite different and very interesting example of compound
rhythm, occurs in the little rills which, at low tide, run over the sand
out of the shingle banks above. Where the channel of one of these is
narrow, and the stream runs strongly, the sand at the bottom is raised
into a series of ridges corresponding to the ripple of the water. On
watching for a short time, it will be seen that these ridges are being
raised higher and the ripple growing stronger; until at length, the
action becoming violent, the whole series of ridges is suddenly swept
away, the stream runs smoothly, and the process commences afresh.
Instances of still more complex rhythms might be added; but they will
come more appropriately in connexion with the several forms of
Evolution, hereafter to be dealt with.
From the ensemble of the facts as above set forth, it will be seen that
rhythm results wherever there is a conflict of forces not in
equilibrium. If the antagonist forces at any point are balanced, there
is rest; and in the absence of motion there can of course be no rhythm.
But if instead of a balance there is an excess of force in one
direction—if, as necessarily follows, motion is set up in that
direction; then for that motion to continue uniformly in that direction,
it is requisite that the moving matter should, notwithstanding its
unceasing change of place, present unchanging relations to the sources
of force by which its motion is produced and opposed. This however is
impossible. Every further transfer through space must alter the ratio
between the forces concerned—must increase or decrease the predominance
of one force over the other—must prevent uniformity of movement. And if
the movement cannot be uniform, then, in the absence of acceleration or
retardation continued through infinite time and space, (results which
cannot be conceived) the only alternative is rhythm.
A secondary conclusion must not be omitted. In the last chapter we saw
that motion is never absolutely rectilinear; and here it remains to be
added that, as a consequence, rhythm is necessarily incomplete. A truly
rectilinear rhythm can arise only when the opposing forces are in
exactly the same line; and the probabilities against this are infinitely
great. To generate a perfectly circular rhythm, the two forces concerned
must be exactly at right angles to each other, and must have exactly a
certain ratio; and against this the probabilities are likewise
infinitely great. All other proportions and directions of the two forces
will produce an ellipse of greater or less eccentricity. And when, as
indeed always happens, above two forces are engaged, the curve described
must be more complex; and cannot exactly repeat itself. So that in fact
throughout nature, this action and re-action of forces never brings
about a complete return to a previous state. Where the movement is very
involved, and especially where it is that of some aggregate whose units
are partially independent, anything like a regular curve is no longer
traceable; we see nothing more than a general oscillation. And on the
completion of any periodic movement, the degree in which the state
arrived at differs from the state departed from, is usually marked in
proportion as the influences at work are numerous.
* * * * *
§ 94. That spiral arrangement so general among the more diffused
nebulæ—an arrangement which must be assumed by matter moving towards a
centre of gravity through a resisting medium—shows us the progressive
establishment of revolution, and therefore of rhythm; in those remote
spaces which the nebulæ occupy. Double stars, moving round common
centres of gravity in periods some of which are now ascertained, exhibit
settled rhythmical actions in distant parts of our sidereal system. And
another fact which, though of a different order, has a like general
significance, is furnished by variable stars—stars which alternately
brighten and fade.
The periodicities of the planets, satellites, and comets, are so
familiar that it would be inexcusable to name them, were it not needful
here to point out that they are so many grand illustrations of this
general law of movement. But besides the revolutions of these bodies in
their orbits (all more or less excentric) and their rotations on their
axes, the Solar System presents us with various rhythms of a less
manifest and more complex kind. In each planet and satellite there is
the revolution of the nodes—a slow change in the position of the
orbit-plane, which after completing itself commences afresh. There is
the gradual alteration in the length of the axis major of the orbit; and
also of its excentricity: both of which are rhythmical alike in the
sense that they alternate between maxima and minima, and in the sense
that the progress from one extreme to the other is not uniform, but is
made with fluctuating velocity. Then, too, there is the revolution of
the line of apsides, which in course of time moves round the heavens—not
regularly, but through complex oscillations. And further we have
variations in the directions of the planetary axes—that known as
nutation, and that larger gyration which, in the case of the Earth,
causes the precession of the equinoxes. These rhythms, already
more or less compound, are compounded with each other. Such an instance
as the secular acceleration and retardation of the moon, consequent on
the varying excentricity of the Earth’s orbit, is one of the simplest.
Another, having more important consequences, results from the changing
direction of the axes of rotation in planets whose orbits are decidedly
excentric. Every planet, during a certain long period, presents more of
its northern than of its southern hemisphere to the sun at the time of
its nearest approach to him; and then again, during a like period,
presents more of its southern hemisphere than of its northern—a
recurring coincidence which, though causing in some planets no sensible
alterations of climate, involves in the case of the Earth an epoch of
21,000 years, during which each hemisphere goes through a cycle of
temperate seasons, and seasons that are extreme in their heat and cold.
Nor is this all. There is even a variation of this variation. For the
summers and winters of the whole Earth become more or less strongly
contrasted, as the excentricity of its orbit increases and decreases.
Hence during increase of the excentricity, the epochs of moderately
contrasted seasons and epochs of strongly contrasted seasons, through
which alternately each hemisphere passes, must grow more and more
different in the degrees of their contrasts; and contrariwise during
decrease of the excentricity. So that in the quantity of light and heat
which any portion of the Earth receives from the sun, there goes on a
quadruple rhythm: that of day and night; that of summer and winter; that
due to the changing position of the axis at perihelion and aphelion,
taking 21,000 years to complete; and that involved by the variation of
the orbit’s excentricity, gone through in millions of years.
* * * * *
§ 95. Those terrestrial processes whose dependence on the solar heat is
direct, of course exhibit a rhythm that corresponds to the periodically
changing amount of heat which each part of the Earth receives. The
simplest, though the least obtrusive, instance is supplied by the
magnetic variations. In these there is a diurnal increase and decrease,
an annual increase and decrease, and a decennial increase and decrease;
the latter answering to a period during which the solar spots become
alternately abundant and scarce: besides which known variations there
are probably others corresponding with the astronomical cycles just
described. More obvious examples are furnished by the movements of the
ocean and the atmosphere. Marine currents from the equator to the poles
above, and from the poles to the equator beneath, show us an unceasing
backward and forward motion throughout this vast mass of water—a motion
varying in amount according to the seasons, and compounded with smaller
like motions of local origin. The similarly-caused general currents in
the air, have similar annual variations similarly modified. Irregular as
they are in detail, we still see in the monsoons and other tropical
atmospheric disturbances, or even in our own equinoctial gales and
spring east winds, a periodicity sufficiently decided. Again, we
have an alternation of times during which evaporation predominates with
times during which condensation predominates: shown in the tropics by
strongly marked rainy seasons and seasons of drought, and in the
temperate zones by corresponding changes of which the periodicity,
though less definite, is still traceable. The diffusion and
precipitation of water, besides the slow alternations answering to
different parts of the year, furnish us with examples of rhythm of a
more rapid kind. During wet weather, lasting, let us say, over some
weeks, the tendency to condense, though greater than the tendency to
evaporate, does not show itself in continuous rain; but the period is
made up of rainy days and days that are wholly or partially fair. Nor is
it in this rude alternation only that the law is manifested. During any
day throughout this wet weather a minor rhythm is traceable; and
especially so when the tendencies to evaporate and to condense are
nearly balanced. Among mountains this minor rhythm and its causes may be
studied to great advantage. Moist winds, which do not precipitate their
contained water in passing over the comparatively warm lowlands, lose so
much heat when they reach the cold mountain peaks, that condensation
rapidly takes place. Water, however, in passing from the gaseous to the
fluid state, gives out a considerable amount of heat; and hence the
resulting clouds are warmer than the air that precipitates them, and
much warmer than the high rocky surfaces round which they fold
themselves. Hence in the course of the storm, these high rocky surfaces
are raised in temperature, partly by radiation from the enwrapping
cloud, partly by contact of the falling rain-drops. Giving off more heat
than before, they no longer lower so greatly the temperature of the air
passing over them; and so cease to precipitate its contained water. The
clouds break; the sky begins to clear; and a gleam of sunshine promises
that the day is going to be fine. But the small supply of heat which the
cold mountain’s sides have received, is soon lost: especially when the
dispersion of the clouds permits free radiation into space. Very soon,
therefore, these elevated surfaces, becoming as cold as at first, (or
perhaps even colder in virtue of the evaporation set up,) begin again to
condense the vapour in the air above; and there comes another storm,
followed by the same effects as before. In lowland regions this action
and reaction is usually less conspicuous, because the contrast of
temperatures is less marked. Even here, however, it may be traced; and
that not only on showery days, but on days of continuous rain; for in
these we do not see uniformity: always there are fits of harder and
gentler rain that are probably caused as above explained.
Of course these meteorologic rhythms involve something corresponding to
them in the changes wrought by wind and water on the Earth’s surface.
Variations in the quantities of sediment brought down by rivers that
rise and fall with the seasons, must cause variations in the resulting
strata—alternations of colour or quality in the successive laminæ. Beds
formed from the detritus of shores worn down and carried away by the
waves, must similarly show periodic differences answering to the
periodic winds of the locality. In so far as frost influences the rate
of denudation, its recurrence is a factor in the rhythm of sedimentary
deposits. And the geological changes produced by glaciers and icebergs
must similarly have their alternating periods of greater and less
intensity.
There is evidence also that modifications in the Earth’s crust due to
igneous action have a certain periodicity. Volcanic eruptions are not
continuous but intermittent, and as far as the data enable us to judge,
have a certain average rate of recurrence; which rate of recurrence is
complicated by rising into epochs of greater activity and falling into
epochs of comparative quiescence. So too is it with earthquakes and the
elevations or depressions caused by them. At the mouth of the
Mississippi, the alternation of strata gives decisive proof of
successive sinkings of the surface, that have taken place at tolerably
equal intervals. Everywhere, in the extensive groups of conformable
strata that imply small subsidences recurring with a certain average
frequency, we see a rhythm in the action and reaction between the
Earth’s crust and its molten contents—a rhythm compounded with those
slower ones shown in the termination of groups of strata, and the
commencement of other groups not conformable to them. There is
even reason for suspecting a geological periodicity that is immensely
slower and far wider in its effects; namely, an alternation of those
vast upheavals and submergencies by which continents are produced where
there were oceans, and oceans where there were continents. For
supposing, as we may fairly do, that the Earth’s crust is throughout of
tolerably equal thickness, it is manifest that such portions of it as
become most depressed below the average level, must have their inner
surfaces most exposed to the currents of molten matter circulating
within, and will therefore undergo a larger amount of what may be called
igneous denudation; while, conversely, the withdrawal of the inner
surfaces from these currents where the Earth’s crust is most elevated,
will cause a thickening more or less compensating the aqueous denudation
going on externally. Hence those depressed areas over which the deepest
oceans lie, being gradually thinned beneath and not covered by much
sedimentary deposit above, will become areas of least resistance, and
will then begin to yield to the upward pressure of the Earth’s contents;
whence will result, throughout such areas, long-continued elevations,
ceasing only when the reverse state of things has been brought about.
Whether this speculation be well or ill founded, does not however affect
the general conclusion. Apart from it we have sufficient evidence that
geologic processes are rhythmical.
* * * * *
§ 96. Perhaps nowhere are the illustrations of rhythm so numerous and so
manifest as among the phenomena of life. Plants do not, indeed, usually
show us any decided periodicities, save those determined by day and
night and by the seasons. But in animals we have a great variety of
movements in which the alternation of opposite extremes goes on with all
degrees of rapidity. The swallowing of food is effected by a wave of
constriction passing along the œsophagus; its digestion is accompanied
by a muscular action of the stomach that is also undulatory; and the
peristaltic motion of the intestines is of like nature. The blood
obtained from this food is propelled not in a uniform current but in
pulses; and it is aerated by lungs that alternately contract and expand.
All locomotion results from oscillating movements: even where it is
apparently continuous, as in many minute forms, the microscope proves
the vibration of cilia to be the agency by which the creature is moved
smoothly forwards.
Primary rhythms of the organic actions are compounded with secondary
ones of longer duration. These various modes of activity have their
recurring periods of increase and decrease. We see this in the periodic
need for food, and in the periodic need for repose. Each meal induces a
more rapid rhythmic action of the digestive organs; the pulsation of the
heart is accelerated; and the inspirations become more frequent. During
sleep, on the contrary, these several movements slacken. So that in the
course of the twenty-four hours, those small undulations of which the
different kinds of organic action are constituted, undergo one long wave
of increase and decrease, complicated with several minor waves.
Experiments have shown that there are still slower rises and falls
of functional activity. Waste and assimilation are not balanced by every
meal, but one or other maintains for some time a slight excess; so that
a person in ordinary health is found to undergo an increase and decrease
of weight during recurring intervals of tolerable equality. Besides
these regular periods there are still longer and comparatively irregular
ones; namely, those alternations of greater and less vigour, which even
healthy people experience. So inevitable are these oscillations that
even men in training cannot be kept stationary at their highest power,
but when they have reached it begin to retrograde. Further
evidence of rhythm in the vital movements is furnished by invalids.
Sundry disorders are named from the intermittent character of their
symptoms. Even where the periodicity is not very marked, it is mostly
traceable. Patients rarely if ever get uniformly worse; and
convalescents have usually their days of partial relapse or of less
decided advance.
Aggregates of living creatures illustrate the general truth in other
ways. If each species of organism be regarded as a whole, it displays
two kinds of rhythm. Life as it exists in all the members of such
species, is an extremely complex kind of movement, more or less distinct
from the kinds of movement which constitutes life in other species. In
each individual of the species, this extremely complex kind of movement
begins, rises to its climax, declines, and ceases in death. And every
successive generation thus exhibits a wave of that peculiar activity
characterizing the species as a whole. The other form of rhythm is
to be traced in that variation of number which each tribe of animals and
plants is ever undergoing. Throughout the unceasing conflict between the
tendency of a species to increase and the antagonistic tendencies, there
is never an equilibrium: one always predominates. In the case even of a
cultivated plant or domesticated animal, where artificial means are used
to maintain the supply at a uniform level, we still see that
oscillations of abundance and scarcity cannot be avoided. And among the
creatures uncared for by man, such oscillations are usually more marked.
After a race of organisms has been greatly thinned by enemies or lack of
food, its surviving members become more favourably circumstanced than
usual. During the decline in their numbers their food has grown
relatively more abundant; while their enemies have diminished from want
of prey. The conditions thus remain for some time favourable to their
increase; and they multiply rapidly. By and by their food is rendered
relatively scarce, at the same time that their enemies have become more
numerous; and the destroying influences being thus in excess, their
number begins to diminish again. Yet one more rhythm, extremely
slow in its action, may be traced in the phenomena of Life, contemplated
under their most general aspect. The researches of palæontologists show,
that there have been going on, during the vast period of which our
sedimentary rocks bear record, successive changes of organic forms.
Species have appeared, become abundant, and then disappeared. Genera, at
first constituted of but few species, have for a time gone on growing
more multiform; and then have begun to decline in the number of their
subdivisions; leaving at last but one or two representatives, or none at
all. During longer epochs whole orders have thus arisen, culminated, and
dwindled away. And even those wider divisions containing many orders
have similarly undergone a gradual rise, a high tide, and a
long-continued ebb. The stalked _Crinoidea_, for example, which, during
the carboniferous epoch, became abundant, have almost disappeared: only
a single species being extant. Once a large family of molluscs, the
_Brachiopoda_ have now become rare. The shelled Cephalopods, at one time
dominant among the inhabitants of the ocean, both in number of forms and
of individuals, are in our day nearly extinct. And after an “age of
reptiles,” there has come an age in which reptiles have been in great
measure supplanted by mammals. Whether these vast rises and falls of
different kinds of life ever undergo anything approaching to
repetitions, (which they may possibly do in correspondence with those
vast cycles of elevation and subsidence that produce continents and
oceans,) it is sufficiently clear that Life on the Earth has not
progressed uniformly, but in immense undulations.
* * * * *
§ 97. It is not manifest that the changes of consciousness are in any
sense rhythmical. Yet here, too, analysis proves both that the mental
state existing at any moment is not uniform, but is decomposable into
rapid oscillations; and also that mental states pass through longer
intervals of increasing and decreasing intensity.
Though while attending to any single sensation, or any group of related
sensations constituting the consciousness of an object, we seem to
remain for the time in a persistent and homogeneous condition of mind, a
careful self-examination shows that this apparently unbroken mental
state is in truth traversed by a number of minor states, in which
various other sensations and perceptions are rapidly presented and
disappear. From the admitted fact that thinking consists in the
establishment of relations, it is a necessary corollary that the
maintenance of consciousness in any one state to the entire exclusion of
other states, would be a cessation of thought, that is, of
consciousness. So that any seemingly continuous feeling, say of
pressure, really consists of portions of that feeling perpetually
recurring after the momentary intrusion of other feelings and
ideas—quick thoughts concerning the place where it is felt, the external
object producing it, its consequences, and other things suggested by
association. Thus there is going on an extremely rapid departure from,
and return to, that particular mental state which we regard as
persistent. Besides the evidence of rhythm in consciousness which direct
analysis thus affords, we may gather further evidence from the
correlation between feeling and movement. Sensations and emotions expend
themselves in producing muscular contractions. If a sensation or emotion
were strictly continuous, there would be a continuous discharge along
those motor nerves acted upon. But so far as experiments with artificial
stimuli enable us to judge, a continuous discharge along the nerve
leading to a muscle, does not contract it: a broken discharge is
required—a rapid succession of shocks. Hence muscular contraction
pre-supposes that rhythmic state of consciousness which direct
observation discloses. A much more conspicuous rhythm, having
longer waves, is seen during the outflow of emotion into dancing,
poetry, and music. The current of mental energy that shows itself in
these modes of bodily action, is not continuous, but falls into a
succession of pulses. The measure of a dance is produced by the
alternation of strong muscular contractions with weaker ones; and, save
in measures of the simplest order such as are found among barbarians and
children, this alternation is compounded with longer rises and falls in
the degree of muscular excitement. Poetry is a form of speech which
results when the emphasis is regularly recurrent; that is, when the
muscular effort of pronunciation has definite periods of greater and
less intensity—periods that are complicated with others of like nature
answering to the successive verses. Music, in still more various ways,
exemplifies the law. There are the recurring bars, in each of which
there is a primary and a secondary beat. There is the alternate increase
and decrease of muscular strain, implied by the ascents and descents to
the higher and lower notes—ascents and descents composed of smaller
waves, breaking the rises and falls of the larger ones, in a mode
peculiar to each melody. And then we have, further, the alternation of
_piano_ and _forte_ passages. That these several kinds of rhythm,
characterizing æsthetic expression, are not, in the common sense of the
word, artificial, but are intenser forms of an undulatory movement
habitually generated by feeling in its bodily discharge, is shown by the
fact that they are all traceable in ordinary speech; which in every
sentence has its primary and secondary emphases, and its cadence
containing a chief rise and fall complicated with subordinate rises and
falls; and which is accompanied by a more or less oscillatory action of
the limbs when the emotion is great. Still longer undulations may
be observed by every one, in himself and in others, on occasions of
extreme pleasure or extreme pain. Note, in the first place, that pain
having its origin in bodily disorder, is nearly always perceptibly
rhythmical. During hours in which it never actually ceases, it has its
variations of intensity—fits or paroxysms; and then after these hours of
suffering there usually come hours of comparative ease. Moral pain has
the like smaller and larger waves. One possessed by intense grief does
not utter continuous moans, or shed tears with an equable rapidity; but
these signs of passion come in recurring bursts. Then after a time
during which such stronger and weaker waves of emotion alternate, there
comes a calm—a time of comparative deadness; to which again succeeds
another interval, when dull sorrow rises afresh into acute anguish, with
its series of paroxysms. Similarly in great delight, especially as
manifested by children who have its display less under control, there
are visible variations in the intensity of feeling shown—fits of
laughter and dancing about, separated by pauses in which smiles, and
other slight manifestations of pleasure, suffice to discharge the
lessened excitement. Nor are there wanting evidences of mental
undulations greater in length than any of these—undulations which take
weeks, or months, or years, to complete themselves. We continually hear
of moods which recur at intervals. Very many persons have their epochs
of vivacity and depression. There are periods of industry following
periods of idleness; and times at which particular subjects or tastes
are cultivated with zeal, alternating with times at which they are
neglected. Respecting which slow oscillations, the only qualification to
be made is, that being affected by numerous influences, they are
comparatively irregular.
* * * * *
§ 98. In nomadic societies the changes of place, determined as they
usually are by exhaustion or failure of the supply of food, are
periodic; and in many cases show a recurrence answering to the seasons.
Each tribe that has become in some degree fixed in its locality, goes on
increasing, till under the pressures of unsatisfied desires, there
results migration of some part of it to a new region—a process repeated
at intervals. From such excesses of population, and such successive
waves of migration, come conflicts with other tribes; which are also
increasing and tending to diffuse themselves. This antagonism, like all
others, results not in an uniform motion, but in an intermittent one.
War, exhaustion, recoil—peace, prosperity, and renewed aggression:—see
here the alternation more or less discernible in the military activities
of both savage and civilized nations. And irregular as is this rhythm,
it is not more so than the different sizes of the societies, and the
extremely involved causes of variation in their strengths, would lead us
to anticipate.
Passing from external to internal changes, we meet with this backward
and forward movement under many forms. In the currents of commerce it is
especially conspicuous. Exchange during early times is almost wholly
carried on at fairs, held at long intervals in the chief centres of
population. The flux and reflux of people and commodities which each of
these exhibits, becomes more frequent as national development leads to
greater social activity. The more rapid rhythm of weekly markets begins
to supersede the slow rhythm of fairs. And eventually the process of
exchange becomes at certain places so active, as to bring about daily
meetings of buyers and sellers—a daily wave of accumulation and
distribution of cotton, or corn, or capital. If from exchange we
turn to production and consumption, we see undulations, much longer
indeed in their periods, but almost equally obvious. Supply and demand
are never completely adapted to each other; but each of them from time
to time in excess, leads presently to an excess of the other. Farmers
who have one season produced wheat very abundantly, are disgusted with
the consequent low price; and next season, sowing a much smaller
quantity, bring to market a deficient crop; whence follows a converse
effect. Consumption undergoes parallel undulations that need not be
specified. The balancing of supplies between different districts, too,
entails analogous oscillations. A place at which some necessary of life
is scarce, becomes a place to which currents of it are set up from other
places where it is relatively abundant; and these currents from all
sides lead to a wave of accumulation where they meet—a glut: whence
follows a recoil—a partial return of the currents. But the
undulatory character of these actions is perhaps best seen in the rises
and falls of prices. These, given in numerical measures which may be
tabulated and reduced to diagrams, show us in the clearest manner how
commercial movements are compounded of oscillations of various
magnitudes. The price of consols or the price of wheat, as thus
represented, is seen to undergo vast ascents and descents whose highest
and lowest points are reached only in the course of years. These largest
waves of variation are broken by others extending over periods of
perhaps many months. On these again come others having a week or two’s
duration. And were the changes marked in greater detail, we should have
the smaller undulations that take place each day, and the still smaller
ones which brokers telegraph from hour to hour. The whole outline would
show a complication like that of a vast ocean-swell, on whose surface
there rise large billows, which themselves bear waves of moderate size,
covered by wavelets, that are roughened by a minute ripple. Similar
diagrammatic representations of births, marriages, and deaths, of
disease, of crime, of pauperism, exhibit involved conflicts of
rhythmical motions throughout society under these several aspects.
There are like characteristics in social changes of a more complex kind.
Both in England and among continental nations, the action and reaction
of political progress have come to be generally recognized. Religion,
besides its occasional revivals of smaller magnitude, has its long
periods of exaltation and depression—generations of belief and
self-mortification, following generations of indifference and laxity.
There are poetical epochs, and epochs in which the sense of the
beautiful seems almost dormant. Philosophy, after having been awhile
predominant, lapses for a long season into neglect; and then again
slowly revives. Each science has its eras of deductive reasoning, and
its eras when attention is chiefly directed to collecting and
colligating facts. And how in such minor but more obtrusive phenomena as
those of fashion, there are ever going on oscillations from one extreme
to the other, is a trite observation.
As may be foreseen, social rhythms well illustrate the irregularity that
results from combination of many causes. Where the variations are those
of one simple element in national life, as the supply of a particular
commodity, we do indeed witness a return, after many involved movements,
to a previous condition—the price may become what it was before:
implying a like relative abundance. But where the action is one into
which many factors enter, there is never a recurrence of exactly the
same state. A political reaction never brings round just the old form of
things. The rationalism of the present day differs widely from the
rationalism of the last century. And though fashion from time to time
revives extinct types of dress, these always re-appear with decided
modifications.
* * * * *
§ 99. The universality of this principle suggests a question like that
raised in foregoing cases. Rhythm being manifested in all forms of
movement, we have reason to suspect that it is determined by some
primordial condition to action in general. The tacit implication is that
it is deducible from the persistence of force. This we shall find to be
the fact.
When the prong of a tuning-fork is pulled on one side by the finger, a
certain extra tension is produced among its cohering particles; which
resist any force that draws them out of their state of equilibrium. As
much force as the finger exerts in pulling the prong aside, so much
opposing force is brought into play among the cohering particles. Hence,
when the prong is liberated, it is urged back by a force equal to that
used in deflecting it. When, therefore, the prong reaches its original
position, the force impressed on it during its recoil, has generated in
it a corresponding amount of momentum—an amount of momentum nearly
equivalent, that is, to the force originally impressed (nearly, we must
say, because a certain portion has gone in communicating motion to the
air, and a certain other portion has been transformed into heat). This
momentum carries the prong beyond the position of rest, nearly as far as
it was originally drawn in the reverse direction; until at length, being
gradually used up in producing an opposing tension among the particles,
it is all lost. The opposing tension into which the expended momentum
has been transformed, then generates a second recoil; and so on
continually—the vibration eventually ceasing only because at each
movement a certain amount of force goes in creating atmospheric and
etherial undulations. Now it needs but to contemplate this repeated
action and reaction, to see that it is, like every action and reaction,
a consequence of the persistence of force. The force exerted by the
finger in bending the prong cannot disappear. Under what form then does
it exist? It exists under the form of that cohesive tension which it has
generated among the particles. This cohesive tension cannot cease
without an equivalent result. What is its equivalent result? The
momentum generated in the prong while being carried back to its position
of rest. This momentum too—what becomes of it? It must either continue
as momentum, or produce some correlative force of equal amount. It
cannot continue as momentum, since change of place is resisted by the
cohesion of the parts; and thus it gradually disappears by being
transformed into tension among these parts. This is re-transformed into
the equivalent momentum; and so on continuously. If instead of
motion that is directly antagonized by the cohesion of matter, we
consider motion through space, the same truth presents itself under
another form. Though here no opposing force seems at work, and therefore
no cause of rhythm is apparent, yet its own accumulated momentum must
eventually carry the moving body beyond the body attracting it; and so
must become a force at variance with that which generated it. From this
conflict, rhythm necessarily results as in the foregoing case. The force
embodied as momentum in a given direction, cannot be destroyed; and if
it eventually disappears, it re-appears in the reaction on the retarding
body; which begins afresh to draw the now arrested mass back from its
aphelion. The only conditions under which there could be absence of
rhythm—the only conditions, that is, under which there could be a
continuous motion through space in the same straight line for ever,
would be the existence of an infinity void of everything but the moving
body. And neither of these conditions can be represented in thought.
Infinity is inconceivable; and so also is a motion which never had a
commencement in some pre-existing source of power. Thus, then,
rhythm is a necessary characteristic of all motion. Given the
coexistence everywhere of antagonist forces—a postulate which, as we
have seen, is necessitated by the form of our experience—and rhythm is
an inevitable corollary from the persistence of force.
Hence, throughout that re-arrangement of parts which constitutes
Evolution, we must nowhere expect to see the change from one position of
things to another, effected by continuous movement in the same
direction. Be it in that kind of Evolution which the inorganic creation
presents, or in that presented by the organic creation, we shall
everywhere find a periodicity of action and reaction—a backward and
forward motion, of which progress is a differential result.
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Footnote 15:
After having for some years supposed myself alone in the belief that
all motion is rhythmical, I discovered that my friend Professor
Tyndall also held this doctrine.