THE EUROPEAN AGE OF REASON--(_Continued_).
THE UNION OF SCIENCE AND INDUSTRY.
_European Progress in the Acquisition of exact Knowledge.--Its
Resemblance to that of Greece._
_Discoveries respecting the Air.--Its mechanical and chemical
Properties.--Its Relation to Animals and Plants.--The Winds.
--Meteorology.--Sounds.--Acoustic Phenomena._
_Discoveries respecting the Ocean.--Physical and chemical
Phenomena.--Tides and Currents.--Clouds.--Decomposition of Water._
_Discoveries respecting other material Substances.--Progress of
Chemistry._
_Discoveries respecting Electricity. Magnetism, Light, Heat._
_Mechanical Philosophy and Inventions.--Physical Instruments.--The
Result illustrated by the Cotton Manufacture.--Steam-engine.--Bleaching.
--Canals.--Railways.--Improvements in the Construction of
Machinery.--Social Changes produced.--Its Effect on intellectual
Activity._
_The scientific Contributions of various Nations, and especially of
Italy._
The Age of Reason in Europe presents all the peculiarities of the Age of
Reason in Greece. There are modern representatives of King Ptolemy
Philadelphus among his furnaces and crucibles; of Hipparchus cataloguing
the stars; of Aristyllus and Timochares, with their stone quadrants and
armils, ascertaining the planetary motions; of Eratosthenes measuring
the size of the earth; of Herophilus dissecting the human body; of
Archimedes settling the laws of mechanics and hydrostatics; of Manetho
collating the annals of the old dynasties of Egypt; of Euclid and
Apollonius improving mathematics. [Sidenote: Analogies between the Age
of Reason in Europe and in Greece.] There are botanical gardens and
zoological menageries like those of Alexandria, and expeditions to the
sources of the Nile. The direction of thought is the same; but the
progress is on a greater scale, and illustrated by more imposing
results. The exploring voyages to Madagascar are replaced by
circumnavigations of the world; the revolving steam-engine of Hero by
the double-acting engine of Watt; the great galley of Ptolemy, with its
many banks of rowers, by the ocean steam-ship; the solitary watch-fire
on the Pharos by a thousand light-houses, with their fixed and revolving
lights; the courier on his Arab horse by the locomotive and electric
telegraph; the scriptorium in the Serapion, with its shelves of papyrus,
by countless printing-presses; the "Almagest" of Ptolemy by the
"Principia" of Newton; and the Museum itself by English, French,
Italian, German, Dutch, and Russian philosophical societies,
universities, colleges, and other institutions of learning.
[Sidenote: European progress in the acquisition of knowledge.] So grand
is the scale on which this cultivation of science has been resumed, so
many are those engaged in it, so rapid is the advance, and so great are
the material advantages, that there is no difficulty in appreciating the
age of which it is the characteristic. The most superficial outline
enables us to recognize at once its resemblance to that period of Greek
life to which I have referred. To bring its features into relief, I
shall devote a few pages to a cursory review of the progress of some of
the departments of science, selecting for the purpose topics of general
interest.
First, then, as respects the atmosphere, and the phenomena connected
with it.
[Sidenote: The atmosphere.] From observations on the twilight, the
elasticity of aerial bodies, and the condensing action of cold, the
conclusion previously arrived at by Alhazen was established, that the
atmosphere does not extend unlimitedly into space. Its height is
considered to be about forty-five miles. From its compressibility, the
greater part of it is within a much smaller limit; were it of uniform
density, it would not extend more than 29,000 feet. Hence, comparing it
with the dimensions of the earth, it is an insignificant aerial shell,
in thickness not the eightieth part of the distance to the earth's
centre, and its immensity altogether an illusion. It bears about the
same proportion to the earth, that the down upon a peach bears to the
peach itself.
A foundation for the mechanical theory of the atmosphere was laid as
soon as just ideas respecting liquid pressures, as formerly taught by
Archimedes, were restored, the conditions of vertical and oblique
pressures investigated, the demonstration of equality of pressures in
all directions given, and the proof furnished that the force of a liquid
on the bottom of a vessel may be very much greater than its weight.
[Sidenote: Its mechanical relations.] Such of these conclusions as were
applicable were soon transferred to the case of aerial bodies. The
weight of the atmosphere was demonstrated, its pressure illustrated and
measured; then came the dispute about the action of pumps, and the
overthrow of the Aristotelian doctrine of the horror of a vacuum.
Coincidently occurred the invention of the barometer, and the proof of
its true theory, both on a steeple in Paris and on a mountain in
Auvergne. The invention of the air-pump, and its beautiful illustrations
of the properties of the atmosphere, extended in a singular manner the
taste for natural philosophy.
[Sidenote: Its chemical relations.] The mechanics of the air was soon
followed by its chemistry. From remote ages it had been numbered among
the elements, though considered liable to vitiation or foulness. The
great discovery of oxygen gas placed its chemical relations in their
proper position. One after another, other gases, both simple and
compound, were discovered. Then it was recognized that the atmosphere is
the common receptacle for all gases and vapours, and the problem
whether, in the course of ages, it has ever undergone change in its
constitution arose for solution.
[Sidenote: The antagonism of animals and plants.] The negative
determination of that problem, so far as a few thousand years are
concerned, was necessarily followed by a recognition of the antagonism
of animals and plants, and their mutually balancing each other, the
latter accomplishing their duty under the influence of the sun, though
he is a hundred millions of miles distant. From this it appeared that it
is not by incessant interventions that the sum total of animal life is
adjusted to that of vegetable, but that, in this respect, the system of
government of the world is by the operation of natural causes and law, a
conclusion the more imposing since it contemplates all living things,
and includes even man himself. The detail of these investigations proved
that the organic substance of plants is condensed from the inorganic air
to which that of all animals returns, the particles running in
ever-repeating cycles, now in the air, now in plants, now in animals,
now in the air again, the impulse of movement being in the sun, from
whom has come the force incorporated in plant tissues, and eventually
disengaged in our fires, shining in our flames, oppressing us in fevers,
and surprising us in blushes.
[Sidenote: The winds; their origin and nature.] Organic disturbances by
respiration and the growth of plants being in the lowest stratum of the
air, its uniformity of composition would be impossible were it not for
the agency of the winds and the diffusion of gases, which it was found
would take place under any pressure. The winds were at length properly
referred to the influence of the sun, whose heat warms the air, causing
it to ascend, while other portions flow in below. The explanation of
land and sea breezes was given, and in the trade-wind was found a proof
of the rotation of the earth. At a later period followed the explanation
of monsoons in the alternate heating and cooling of Asia and Africa on
opposite sides of the line, and of tornadoes, which are disks of air
rotating round a translated axis with a diameter of one hundred or one
hundred and fifty miles, the axis moving in a curvilinear track with a
progressive advance of twenty or twenty-five miles an hour, and the
motions being in opposite directions in opposite hemispheres of the
globe.
The equatorial calms and trade-winds accounted for on physical
principles, it was admitted that the winds of high latitudes,
proverbially uncertain as they are, depend in like manner on physical
causes.
With these palpable movements there are others of a less obvious kind.
Through the air, and by reason of motions in it, sounds are transmitted
to us.
[Sidenote: Of sounds; their velocity.] The Alexandrian mathematicians
made sound a favourite study. Modern acoustics arose from the
recognition that there is nothing issuing from the sounding body, but
that its parts are vibrating and affecting the medium between it and the
ear. Not only by the air-pump, but also by observations in the rare
atmosphere of the upper regions, it was shown that the intensity of
sound depends upon the density. On the top of a mountain the report of a
pistol is no louder than that of a cracker in the valley. As to the
gradual propagation of sounds, it was impossible to observe fire-arms
discharged at a distance without noticing that the flash appears longer
before the report in proportion as the distance is greater. The
Florentine academicians attempted a determination of the velocity, and
found it to be 1148 feet in a second. More accurate and recent
experiments made it 1089.42 feet at the freezing-point of water; but the
velocity, though independent of the density, increases with the
temperature at the rate of 1.14 foot for each degree. For other media
the rate is different; for water, about 4687 feet in a second, and in
cast iron about 10-1/2 times greater than in air. All sounds,
irrespective of their note or intensity, move at the same velocity, the
medium itself being motionless in the mass. No sound can pass through a
vacuum. The sudden aerial condensation attending the propagation of a
sound gives rise to a momentary evolution of heat, which increases the
elasticity of the air, and hence the velocity is higher than 916 feet in
a second, otherwise the theoretical rate.
[Sidenote: Acoustic phenomena.] Turning from soniferous media to
sounding bodies, it was shown that the difference between acute and
grave sounds depends on the frequency of vibration. The ear can not
perceive a sound originating in less than thirty-two vibrations in a
second, nor one of more than 24,000. The actual number of vibrations in
a given note was counted by means of revolving wheels and other
contrivances. I have not space to relate the investigation of many other
acoustic facts, the reference of sounds to phases of condensation, and
rarefaction in the elastic medium taking place in a normal direction;
the affections of note, intensity, quality; the passage in curved lines
and around obstacles; the production of sympathetic sounds; nodal
points; the effect of reeds; the phenomena of pipes and flutes, and
other wind instruments; the various vibrations of solids, as bells; or
of membranes, as drums; visible acoustic lines; the reflexion of
undulations by surfaces of various forms; their interferences, so that,
no matter how intense they may be individually, they can be caused to
produce silence; nor of whispering galleries, echoes, the nature of
articulate sounds, the physiology of the vocal and auditory organs of
man, and the construction of speaking machines.
[Sidenote: The ocean; its size.] Like the air, the ocean, which covers
three-fourths of the earth's surface, when reduced to a proper standard
of measure, loses very much of its imposing aspect. The varnish that
covers a twelve-inch globe represents its relative dimension not
inadequately.
[Sidenote: Tides and currents.] On the theory of gravitation, the tides
of the ocean were explained as depending on the attractive force of the
sun and moon. Its currents, in a general manner, are analogous to those
of the air. They originate in the disturbing action of solar heat, the
temperature of the sea varying from 85 deg. in the torrid zone to the
freezing-point as the poles are approached. Its specific gravity at the
equator is estimated at 1.028; but this density necessarily varies with
the rate at which superficial evaporation takes place; the pure vapour
rising, leaves a more concentrated salt solution. The effect is
therefore, in some degree, to counteract the expansion of the water by
warmth, for the sun-rays, being able to penetrate several feet below the
surface, correspondingly raise the temperature of that portion, which
expands and becomes lighter; but, simultaneously, surface evaporation
tends to make the water heavier. Notwithstanding this, currents are
established through the preponderance of the dilatation, and of them the
Gulf Stream is to us the most striking example.
[Sidenote: Effects of ocean streams.] The physical action of the
sun-rays in occasioning currents operates through the expansion of
water, of which warm portions ascend to the surface, colder portions
from beneath setting in to supply their place. These currents, both hot
and cold, are affected by the diurnal rotation of the earth, the action
being essentially the same as that for the winds. They exert so great an
influence as conveyers of heat that they disturb the ordinary climate
relation depending on the sun's position. In this way the Gulf Stream, a
river of hot water in a sea of cold, as soon as it spreads out on the
surface of the Atlantic in higher latitudes, liberates into the air the
heat it has brought from the torrid zone; and this, being borne by the
south-west wind, which blows in those localities for the greater part of
the year, to the westerly part of the European continent, raises by many
degrees the mean annual temperature, thus not only regulating the
distribution of animals and plants, but also influencing human life and
its pursuits, making places pleasant that would otherwise be inclement,
and even facilitating the progress of civilization. Whatever, therefore,
can affect the heat, the volume, the velocity, the direction of such a
stream, at once produces important consequences in the organic world.
[Sidenote: Physical and chemical relations of water.] The Alexandrian
school had attained correct ideas respecting the mechanical properties
of water as the type of liquids. This knowledge was, however, altogether
lost in Europe for many ages, and not regained until the time of
Stevinus and Galileo, who recovered correct views of the nature of
pressure, both vertical and oblique, and placed the sciences of
hydrostatics and hydrodynamics on exact foundations. The Florentine
academicians, from their experiments on water inclosed in a globe of
gold, concluded that it is incompressible, an error subsequently
corrected, and its compressibility measured. The different states in
which it occurs, as ice, water, steam, were shown to depend altogether
on the amount of latent heat it contains. Out of these investigations
originated the invention of the steam-engine, of which it may be said
that it has revolutionized the industry of the world. Soon after the
explanation of the cause of its three states followed the great
discovery that the opinion of past ages respecting its elementary nature
is altogether erroneous. It is not a simple element, but is composed of
two ingredients, oxygen and hydrogen, as was rigorously proved by
decomposing and forming it. By degrees, more correct views of the nature
of evaporation were introduced; gases and vapours were found to coexist
in the same space, not because of their mutual solvent power, but
because of their individual and independent elasticity. The
instantaneous formation of vapours in a vacuum showed that the
determining condition is heat, the weight of vapour capable of existing
in a given space being proportional to the temperature. More scientific
views of the nature of maximum density were obtained, and on these
principles was effected the essential improvement of the low pressure
steam-engine--the apparent paradox of condensing the steam without
cooling the cylinder.
In like manner much light was cast on the meteorological functions of
water. It was seen that the diurnal vaporization from the earth depends
on the amount of heat received, the vapour rising invisibly in the air
till it reaches a region where the temperature is sufficiently low.
There condensation into vesicles of perhaps 1/50000 of an inch in
diameter ensues, and of myriads of such globules a cloud is composed.
[Sidenote: Clouds and their nomenclature.] Of clouds, notwithstanding
their many forms and aspects, a classification was given--cirrus,
cumulus, stratus, etc. It was obvious why some dissolve away and
disappear when they encounter warmer or drier spaces, and why others
descend as rain. It was shown that the drops can not be pure, since they
come in contact with dust, soluble gases, and organic matter in the air.
[Sidenote: The return of water to the sea.] Sinking into the ground, the
water issues forth as springs, contaminated with whatever is in the
soil, and finds its way, through streamlets and rivers, back to the sea,
and thus the drainage of countries is accomplished. Through such a
returning path it comes to the receptacle from which it set out; the
heat of the sun raised it from the ocean, the attraction of the earth
returns it thereto; and, since the heat-supply is invariable from year
to year, the quantity set in motion must be the same. Collateral results
of no little importance attend these movements. Every drop of rain
falling on the earth disintegrates and disturbs portions of the soil;
every stream carries solid matter into the sea. It is the province of
geology to estimate the enormous aggregate of detritus, continents
washed away and new continents formed, and the face of the earth
remodelled and renewed.
[Sidenote: Progress of chemistry.] The artificial decomposition of water
constitutes an epoch in chemistry. The European form of this science, in
contradistinction to the Arabian, arose from the doctrine of acids and
alkalies, and their neutralization. This was about A.D. 1614. It was
perceived that the union of bodies is connected with the possession of
opposite qualities, and hence was introduced the idea of an attraction
of affinity. On this the discovery of elective attraction followed. Then
came the recognition that this attraction is connected with opposite
electrical states, chemistry and electricity approaching each other. A
train of splendid discoveries followed; metals were obtained light
enough to float on water, and even apparently to accomplish the
proverbial impossibility of setting it on fire. In the end it was shown
that the chemical force of electricity is directly proportional to its
absolute quantity. [Sidenote: Attraction. The elements.] Better views of
the nature of chemical attraction were attained, better views of the
intrinsic nature of bodies. The old idea of four elements was discarded,
as also the Saracenic doctrine of salt, sulphur, and mercury. The
elements were multiplied until at length they numbered more than sixty.
[Sidenote: Theory of phlogiston.] Alchemy merged into chemistry through
the theory of phlogiston, which accounted for the change that metals
undergo when exposed to the fire on the principle that something was
driven off from them--a something that might be restored again by the
action of combustible bodies. It is remarkable how adaptive this theory
was. It was found to include the cases of combustive operations, the
production of acids, the breathing of animals. It maintained its ground
even long after the discovery of oxygen gas, of which one of the first
names was dephlogisticated air.
But a false theory always contains within itself the germ of its own
destruction. The weak point of this was, that when a metal is burnt the
product ought to be lighter than the metal, whereas it proves heavier.
[Sidenote: Introduction of the balance into chemistry.] At length it was
detected that what the metal had gained the surrounding air had lost.
This discovery implied that the balance had been resorted to for the
determination of weights and for the decision of physical questions. The
reintroduction of that instrument--for, as we have seen, it had ages
before been employed by the Saracen philosophers, who used several
different forms of it--marked the epoch when chemistry ceased to be
exclusively a science of quality and became one of quantity.
[Sidenote: Theory of oxygen, and the nomenclature.] On the ruins of the
phlogistic theory arose the theory of oxygen, which was sustained with
singular ability. Its progress was greatly facilitated by the
promulgation of a new nomenclature in conformity to its principles, and
of remarkable elegance and power. In the course of time it became
necessary, however, to modify the theory, especially by deposing oxygen
from the attitude of sovereignty to which it had been elevated, and
assigning to it several colleagues, such as chlorine, iodine, etc. The
introduction of the balance was also followed by important consequences
in theoretical chemistry, among which pre-eminently was the
establishment of the laws of combinations of bodies.
[Sidenote: Present state of chemistry.] Extensive and imposing as is the
structure of chemistry, it is very far from its completion. It is so
surrounded by the scaffolding its builders are using, it is so deformed
with the materials of their work, that its true plan can not yet be made
out. In this respect it is far more backward than astronomy. It has,
however, disposed of the idea of the destruction and creation of matter.
[Sidenote: Indestructibility of matter.] It accepts without hesitation
the doctrine of the imperishability of substance; for, though the aspect
of a thing may change through decompositions and recombinations, in
which its constituent parts are concerned, every atom continues to
exist, and may be recovered by suitable processes, though the entire
thing may have seemingly disappeared. A particle of water raised from
the sea may ascend invisibly through the air, it may float above us in
the cloud, it may fall in the rain-drop, sink into the earth, gush forth
again in the fountain, enter the rootlets of a plant, rise up with the
sap to the leaves, be there decomposed by the sunlight into its
constituent elements, its oxygen and hydrogen; of these and other
elements, acids and oils, and various organic compounds may be made: in
these or in its undecomposed state it may be received in the food of
animals, circulate in their blood, be essentially concerned in acts of
intellection executed by the brain, it may be expired in the breath.
Though shed in the tear in moments of despair, it may give birth to the
rainbow, the emblem of hope. Whatever the course through which it has
passed, whatever mutations it has undergone, whatever the force it has
submitted to, its elementary constituents endure. Not only have they not
been annihilated, they have not even been changed; and in a period of
time, long or short, they find their way as water back again to the sea
from which they came.
[Sidenote: Electrical discoveries.] Discoveries in electricity not only
made a profound impression on chemistry, they have taken no
insignificant share in modifying human opinion on other very interesting
subjects. In all ages the lightning had been looked upon with
superstitious dread. The thunderbolt had long been feigned to be the
especial weapon of Divinity. A like superstitious sentiment had
prevailed respecting the northern lights universally regarded in those
countries in which they display themselves as glimpses of the movements
of the angelic host, the banners and weapons of the armies of heaven. A
great blow against superstition was struck when the physical nature of
these phenomena was determined. As to the connexion of electrical
science with the progress of civilization, what more needs to be said
than to allude to the telegraph?
[Sidenote: Theories of electricity.] It is an illustration of the
excellence and fertility of modern methods that the phenomena of the
attraction displayed by amber, which had been known and neglected for
two thousand years, in one-tenth of that time led to surprising results.
[Sidenote: Electrical phenomena.] First it was shown that there are many
other bodies which will act in like manner; then came the invention of
the electrical machine, the discovery of electrical repulsion, and the
spark; the differences of conductibility in bodies; the apparently two
species of electricity, vitreous and resinous; the general law of
attraction and repulsion; the wonderful phenomena of the Leyden phial
and the electric shock; the demonstration of the identity of lightning
and electricity; the means of protecting buildings and ships by rods;
the velocity of electric movement--that immense distances can be passed
through in an inappreciable time; the theory of one fluid and that of
two; the mathematical discussion of all the phenomena, first on one and
then on the other of these doctrines; the invention of the torsion
balance; the determination that the attractive and repulsive forces
follow the law of the inverse squares; the conditions of distribution on
conductors; the elucidation of the phenomena of induction. [Sidenote:
Voltaic electricity.] At length, when discovery seemed to be pausing,
the facts of galvanism were announced in Italy. Up to this time it was
thought that the most certain sign of the death of an animal was its
inability to exhibit muscular contraction: but now it was shown that
muscular movements could be excited in those that are dead and even
mutilated. Then followed quickly the invention of the Voltaic pile.
[Sidenote: Results of the discovery of Galvani.] Who could have foreseen
that the twitching of a frog's leg in the Italian experiments would
establish beyond all question the compound nature of water, separating
its constituents from one another? would lead to the deflagration and
dissipation in a vapour of metals that could hardly be melted in a
furnace? would show that the solid earth we tread upon is an oxide?
yield new metals light enough to swim upon water, and even seem to set
it on fire? produce the most brilliant of all artificial lights,
rivalling if not excelling, in its intolerable splendour the noontide
sun? would occasion a complete revolution in chemistry, compelling that
science to accept new ideas, and even a new nomenclature? that it would
give us the power of making magnets capable of lifting more than a ton,
and cast a light on that riddle of ages, the pointing of the mariner's
compass north and south, explain the mutual attraction or repulsion of
magnetic needles? that it would enable us to form exquisitely in metal
casts of all kinds of objects of art, and give workmen a means of
gilding and silvering without risk to their health? that it would
suggest to the evil disposed the forging of bank notes, the
sophisticating of jewelry, and be invaluable in the uttering of false
coinage? that it would carry the messages of commerce and friendship
instantaneously across continents or under oceans, and "waft a sigh from
Indus to the pole?"
Yet this is only a part of what the Italian experiment, carried out by
modern methods, has actually done. Could there be a more brilliant
exhibition of their power, a brighter earnest of the future of material
philosophy?
[Sidenote: Discoveries in magnetism.] As it had been with amber, so with
the magnet. Its properties had lain uninvestigated for two thousand
years, except in China, where the observation had been made that its
qualities may be imparted to steel, and that a little bar or needle so
prepared, if floated on the surface of water or otherwise suspended,
will point north and south. In that manner the magnet had been applied
in the navigation of ships, and in journeys across trackless deserts.
The first European magnetical discovery was that of Columbus, who
observed a line of no variation west of the Azores. Then followed the
detection of the dip, the demonstration of poles in the needle, and of
the law of attraction and repulsion; the magnetic voyage undertaken by
the English government; the construction of general variation charts;
the observation of diurnal variation; local perturbations; the influence
of the Aurora, which affects all the three expressions of magnetical
power; the disturbance of the horary motion simultaneously over
thousands of miles, as from Kasan to Paris. In the meantime, the theory
of magnetism improved as the facts came out. Its germ was the Cartesian
vortices, suggested by the curvilinear forms of iron filings in the
vicinity of magnetic poles. The subsequent mathematical discussion was
conducted upon the same principles as in the case of electricity.
[Sidenote: Electro-magnetism.] Then came the Danish discovery of the
relations of electricity and magnetism, illustrated in England by
rotatory motions, and in France adorned by the electrodynamic theory,
embracing the action of currents and magnets, magnets and magnets,
currents and currents. The generation of magnetism by electricity was
after a little delay followed by its converse, the production of
electricity by magnetism; and thermoelectric currents, arising from the
unequal application or propagation of heat, were rendered serviceable in
producing the most sensitive of all thermometers.
[Sidenote: Of light and optics.] The investigation of the nature and
properties of light rivals in interest and value that of electricity.
What is this agent, light, which clothes the earth with verdure, making
animal life possible, extending man's intellectual sphere, bringing to
his knowledge the forms and colours of things, and giving him
information of the existence of countless myriads of worlds? What is
this light which, in the midst of so many realities, presents him with
so many delusive fictions, which rests the coloured bow against the
cloud--the bow once said, when men transferred their own motives and
actions to the Divinity, to be the weapon of God?
[Sidenote: Optical discoveries.] The first ascertained optical fact was
probably the propagation of light in straight lines. The theory of
perspective, on which the Alexandrian mathematicians voluminously wrote,
implies as much; but agreeably to the early methods of philosophy, which
were inclined to make man the centre of all things, it was supposed that
rays are emitted from the eye and proceed outwardly, not that they come
from exterior objects and pass through the organ of vision inwardly.
Even the great geometer Euclid treated the subject on that erroneous
principle, an error corrected by the Arabians. In the meantime the law
of reflexion had been discovered; that for refraction foiled Alhazen,
and was reserved for a European. Among natural optical phenomena the
form of the rainbow was accounted for, notwithstanding a general belief
in its supernatural origin. Its colours, however, could not be explained
until exact ideas of refrangibility, dispersion, and the composition of
white light were attained. The reflecting telescope was invented; the
recognized possibility of achromatism led to an improvement in the
refractor. A little previously the progressive motion of light had been
proved, first for reflected light by the eclipses of Jupiter's
satellites, then for the direct light of the stars. A true theory of
colours originated with the formation of the solar spectrum; that
beautiful experiment led to the discovery of irrationality of dispersion
and the fixed lines. The phenomena of refraction in the case of Iceland
spar were examined, and the law for the ordinary and extraordinary rays
given. At the same time the polarization of light by double refraction
was discovered. A century later it was followed by polarisation by
reflexion and single refraction, depolarization, irised rings, bright
and black crosses in crystals, and unannealed or compressed glass, the
connexion between optical phenomena and crystalline form, uniaxial
crystals giving circular rings and biaxial oval ones, and circular and
elliptical polarization.
The beautiful colours of soap-bubbles, at first mixed up with those of
striated and dotted surfaces, were traced to their true
condition--thickness. The determination of thickness of a film necessary
to give a certain colour was the first instance of exceedingly minute
measures beautifully executed. These soon became connected with fringes
in shadows, and led to ascertaining the length of waves of light.
[Sidenote: Vision; the functions of the eye.] Meantime more correct
ideas respecting vision were obtained. Alhazen's explanation of the use
of the retina and lens was adopted. This had been the first truly
scientific investigation in physiology. The action of the eye was
reduced to that of the camera-obscura described by Da Vinci, and the old
notion of rays issuing therefrom finally abandoned. It had held its
ground through the deceptive illustration of the magic-lantern. Of this
instrument the name indicates the popular opinion of its nature. In the
stories of necromancers and magicians of the time are to be found traces
of applications to which it was insidiously devoted--the raising of the
dead, spectres skipping along the ground or dancing on the walls and
chimneys, pendulous images, apparitions in volumes of smoke. [Sidenote:
Optical instruments.] These early instruments were the forerunners of
many beautiful inventions of later times--the kaleidoscope, producing
its forms of marvellous symmetry: the stereoscope, aided by photography,
offering the very embodiment of external scenery; the achromatic and
reflecting telescope, to which physical astronomy is so greatly
indebted; and the achromatic microscope, now working a revolution in
anatomy and physiology.
[Sidenote: The undulatory theory.] In its theory optics has presented a
striking contrast to acoustics. Almost from the very beginning it was
recognized that sound is not a material substance emitted from the
sounding body, but only undulations occurring in the air. For long,
optics failed to reach an analogous conclusion. The advancement of the
former science has been from the general principle down to the details,
that of the latter from the details up to the general principle.
That light consists of undulations in an elastic medium was first
inferred in 1664. Soon after, reflexion, refraction, and double
refraction were accounted for on that principle. The slow progress of
this theory was doubtless owing to Newton's supremacy. He gave a
demonstration in the second book of the "Principia" (Prop. 42) that wave
motions must diverge into the unmoved spaces, and carried popular
comprehension with him by such illustrations as that we hear sounds
though a mountain interpose. It was thought that the undulatory theory
was disposed of by the impossibility of seeing through a crooked pipe,
though we can hear through it; or that we cannot look round a corner,
though we can listen round one.
The present century finally established it through the discovery of
interference, the destruction of the emission theory being inevitable
when it was shown that light, interfering under certain circumstances
with light, may produce darkness, as sound added to sound may produce
silence--results arising from the action of undulating motion. The
difficulties presented by polarization were not only removed, but that
class of phenomena was actually made a strong support of the theory. The
discovery that two pencils of oppositely polarized light would not
interfere, led at once to the theory of transverse vibrations. Great
mathematical ability was now required for the treatment of the subject,
and the special consideration of many optical problems from this new
point of view, as, for example, determining the result of transverse
vibrations coming into a medium of different density in different
directions. As the theory of universal gravitation had formerly done, so
now the undulatory theory began to display its power as a physical
truth, enabling geometers to foresee results, and to precede the
experimenter in conclusions. Among earlier results of the kind was the
prediction that both the rays in the biaxial crystal topaz are
extraordinary, and that circular polarization may be produced by
reflexion in a rhomb of glass. The phenomena of depolarization offered
no special difficulty; and many new facts, as those of elliptic
polarization and conical refraction, have since illustrated the power of
the theory.
[Sidenote: The ether and its movements.] Light, then, is the result of
ethereal undulations impinging on the eye. There exists throughout the
universe and among the particles of all bodies an elastic medium, ether.
By reason of the repulsion of its own parts it is uniformly diffused in
a vacuum. In the interior of refracting media it exists in a state of
less elasticity compared with its density than in vacuo. Vibrations
communicated to it in free space are propagated through such media by
the ether in their interior. The parts of shining bodies vibrate as
those of sounding ones, communicating their movement to the ether, and
giving rise to waves in it. They produce in us the sensation of light.
The slower the vibration, the longer the wave; the more frequent, the
shorter. On wave-length colour depends. In all cases the vibrations are
transverse. The undulatory movement passes onward at the rate of 192,000
miles in a second. The mean length of a wave of light is 0.0000219 of an
inch; an extreme red wave is about twice as long as an extreme violet
one. The yellow is intermediate. The vibrations which thus occasion
light are, at a mean, 555 in the billionth of a second. As with the air,
which is motionless when a sound passes through it, the ether is
motionless, though traversed by waves of light. That which moves forward
is no material substance, but only a form, as the waves seen running
along a shaken cord, or the circles that rise and fall, and spread
outwardly when a stone is thrown into water. The wave-like form passes
onward to the outlying spaces, but the water does not rush forward. And
as we may have on the surface of that liquid waves the height of which
is insignificant, or those which, as sailors say, are mountains high in
storms at sea, their amplitude thus differing, so in the midst of the
ether difference of amplitude is manifested to us by difference in the
intensity or brilliancy of light.
[Sidenote: The human eye; its capabilities.] The human eye, exquisitely
constructed as it is, is nevertheless an imperfect mechanism, being
limited in its action. It can only perceive waves of a definite length,
as its fellow organ, the ear, can only distinguish a limited range of
sounds. It can only take note of vibrations that are transverse, as the
ear can only take note of those that are normal. In optics there are two
distinct orders of facts; the actual relations of light itself, and the
physiological relations of our organ of vision, with all its limitations
and imperfections. Light is altogether the creation of the mind. The
ether is one thing, light is another, just as the air is one thing and
sound another. The ether is not composed of the colours of light any
more than the atmospheric air consists of musical notes.
[Sidenote: Chemical influences of light.] To the chemical agency of
light much attention has in recent times been devoted. Already in
photography, it has furnished us an art which, though yet in its
infancy, presents exquisite representations of scenery, past events, the
countenances of our friends. In an almost magical way it evokes
invisible impressions, and gives duration to fleeting shadows. Moreover,
these chemical influences of light give birth to the whole vegetable
world, with all its varied charms of colour, form, and property, and, as
we have seen in the last chapter, on them animal life itself depends.
[Sidenote: Of heat; reflexion; refraction.] The conclusions arrived at
in optics necessarily entered as fundamental ideas in thermotics, or the
science of heat; for radiant heat moves also in straight lines,
undergoes reflexion, refraction, double refraction, polarization, and
hence the theory of transverse vibrations applies to it. Heat is
invisible light, as light is visible heat. Correct notions of radiation
originated with the Florentine academicians, who used concave mirrors;
and, in the cold-ray experiment, masses of ice of five hundred pounds
weight. The refraction of invisible heat was ascertained in consequence
of the invention of the thermoelectric pile. Its polarization and
depolarization soon followed. Already had been demonstrated the
influence of the physical state of radiant surfaces, and that the heat
comes also from a little depth beneath them. [Sidenote: Exchanges of
heat.] The felicitous doctrine of exchanges of heat imparted true ideas
of the nature of calorific equilibrium and the heating and cooling of
bodies, and offered an explanation of many phenomena, as, for instance,
the formation of dew. [Sidenote: The dew, nature of.] This deposit of
moisture occurs after sunset, the more copiously the clearer the sky; it
never appears on a cloudy night; it neither ascends from the ground like
an exhalation, nor descends like a rain. It shows preferences in its
manner of settling, being found on some objects before it is on others.
All these singular peculiarities were satisfactorily explained, and
another of the mysteries, the unaccountable wonders of the Middle Ages,
brought into the attitude of a simple physical fact.
[Sidenote: Incandescence. Physical instruments.] It is impossible, in a
limited space, to relate satisfactorily what has been done respecting
ignition, the production of light by incandescence, the accurate
measurement of the conductibility of bodies, the determination of the
expansions of solids, liquids, gases, under increasing temperature, the
variations of the same substance at different degrees, the heat of
fluidity and elasticity, and specific heat, or to do justice to the
great improvements made in all kinds of instruments--balances,
thermometers, contrivances for linear and angular measures, telescopes,
microscopes, spectroscopes, chronometers, aerostats, telegraphs, and
machinery generally. [Sidenote: Effect of mechanical inventions.] The
tendency in every direction has been to practical applications. More
accurate knowledge implies increasing power, greater wealth, higher
virtue. The morality of man is enhanced by the improvement of his
intellect and by personal independence. Our age has become rational,
industrial, progressive. In its great physical inventions Europe may
securely trust. There is nothing more to fear from Arabian invasions or
Tartar irruptions. The hordes of Asia could be swept away like chaff
before the wind. Let him who would form a correct opinion of the
position of man in the present and preceding phases of his progress
reflect on the losses of Christendom in Asia and Africa, in spite of all
the machinery of an Age of Faith, and the present security of Europe
from every barbarian or foreign attack.
From almost any of the branches of industry facts might be presented
illustrating the benefits arising from the application of physical
discoveries. As an example, I may refer to the cotton manufacture.
[Sidenote: Illustration from the cotton manufacture.] In a very short
time after the mechanical arts were applied to the manufacture of
textile fabrics, so great was the improvement that a man could do more
work in a day than he had previously done in a year. That manufacture
was moreover accompanied by such collateral events as actually
overturned the social condition throughout Europe. Among these were the
invention of the steam-engine, the canal system, the prodigious
development of the iron manufacture, the locomotive, and railroads;
results not due to the placemen and officers to whom that continent had
resigned its annals, whose effigies encumber the streets of its cities,
but to men in the lower walks of life. The assertion is true that James
Watt, the instrument maker, conferred on his native country more solid
benefits than all the treaties she ever made and all the battles she
ever won. Arkwright was a barber, Harrison a carpenter, Brindley a
millwright's apprentice.
[Sidenote: Development of the cotton manufacture in England.] By the
labours of Paul or of Wyatt, who introduced the operation of spinning by
rollers, a principle perfected by Arkwright; by the rotating
carding-engine, first devised by Paul; by the jenny of Highs or
Hargreaves; the water-frame; the mule, invented by Crompton, so greatly
was the cotton manufacture developed as to demand an entire change in
the life of operatives, and hence arose the factory system. [Sidenote:
The steam-engine of Watt.] At a critical moment was introduced Watt's
invention, the steam-engine. His first patent was taken out in 1769, the
same year that Arkwright patented spinning by rollers. Watt's
improvement chiefly consisted in the use of a separate condenser, and
the replacement of atmospheric pressure by that of steam. Still, it was
not until more than twenty years after that this engine was introduced
into factories, and hence it was not, as is sometimes supposed, the
cause of their wonderful increase. It came, however, at a fortunate
time, nearly coincident with the invention of the dressing-machine by
Radcliffe and the power-loom by Cartwright.
[Sidenote: Bleaching by chlorine.] If the production of textile fabrics
received such advantages from mechanics, equally was it favoured by
chemistry in the discovery of bleaching by chlorine. To bleach a piece
of cotton by the action of the air and the sun required from six to
eight months, and a large surface of land must be used as a
bleach-field. The value of land in the vicinity of great towns presented
an insuperable obstacle to such uses. By chlorine the operation could be
completed in the course of a few hours, and in a comparatively small
building, the fibre being beautifully and permanently whitened.
[Sidenote: Calico-printing by cylinders.] Nor were the chemical
improvements restricted to this. Calico-printing, an art practised many
thousand years ago among the Egyptians, was perfected by the operation
of printing from cylinders.
It deserves to be remarked that the cotton manufacture was first
introduced into Europe by the Arabs. Abderrahman III., A.D. 930, caused
it to be commenced in Spain; he also had extensive manufactures of silk
and leather, and interested himself much in the culture of the sugar
cane, rice, the mulberry. One of the most valuable Spanish applications
of cotton was in the invention of cotton paper. The Arabs were also the
authors of the printing of calicoes by wooden blocks, a great
improvement on the old Indian operation of painting by hand.
[Sidenote: Extent of the cotton manufacture.] We may excuse the
enthusiastic literature of the cotton manufacture its boasting, for men
had accomplished works that were nearly God-like. Mr. Baines, writing in
1833, states that the length of yarn spun in one year was nearly five
thousand millions of miles, sufficient to pass round the earth's
circumference more than two hundred thousand times--sufficient to reach
fifty-one times from the earth to the sun. It would encircle the earth's
orbit eight and a half times. The wrought fabrics of cotton exported in
one year would form a girdle for the globe passing eleven times round
the equator, more than sufficient to form a continuous sheet from the
earth to the moon. And, if this was the case thirty years ago, by what
illustrations would it be possible to depict it now (1859), when the
quantity of cotton imported by England alone is more than twelve hundred
millions of pounds?
[Sidenote: Improvements in locomotion.] But such a vast development in
that particular manufacture necessarily implied other improvements,
especially in locomotion and the transmission of intelligence. The
pedlar's pack, the pack-horse, and the cart became altogether
inadequate, and, in succession, were replaced by the canal system of the
last century, and by the steam-boats and railroads of this. [Sidenote:
Brindley's canals.] The engineering triumphs of Brindley, whose canals
were carried across valleys, over or through mountains, above rivers,
excited unbounded admiration in his own times, and yet they were only
the precursors of the railway engineering of ours. As it was, the canal
system proved to be inadequate to the want, and oaken railways, which
had long been used in quarries and coal-pits, with the locomotive
invented by Murdoch in 1784, were destined to supplant them. [Sidenote:
Stephenson's locomotives.] It does not fall within my present purpose to
relate how the locomotion of the whole civilized world was
revolutionized, not by the act of some mighty sovereign or soldier, but
by George Stephenson, once a steam-engine stoker, who, by the invention
of the tubular boiler and the ingenious device of blowing the chimney
instead of the fire, converted the locomotive of the last century,
which, at its utmost speed, could only travel seven miles an hour, into
the locomotive of this, which can accomplish seventy. [Sidenote: The
railway system.] I need not dwell on the collateral improvements, the
introduction of iron for rails, metallic bridges, tubular bridges,
viaducts, and all the prodigies of the existing system of railway
engineering.
[Sidenote: Improvement in the construction of machinery.] It is not only
on account of the gigantic nature of the work it has to execute that the
machinery employed in the great manufactures, such as those of cotton
and iron, is so worthy of our admiration; improvements as respects the
correctness, and even the elegance of its own construction, attract our
attention. It has been truly said of steam-engines that they were never
properly made until they made themselves. In any machine, the excellence
of its performance depends on the accuracy of its construction. Its
parts must be made perfectly true, and, to work smoothly, must work
without error. To accomplish such conditions taxed to its utmost the
mechanical ingenuity of the last century; and, indeed, it was not
possible to reach perfect success so long as the hand alone was resorted
to. Work executed by the most skilful mechanic could be no more than
approximately correct. Not until such machines as the sliding rest and
planing engine were introduced could any approach to perfection be made.
Improvements of this nature reacted at once on the primary construction
of machinery, making it more powerful, more accurate, more durable, and
also led to the introduction of greater elegance in its planning or
conception, as any one may see who will compare the clumsy half wooden,
half metal machinery of the last century with the light and tasteful
constructions of this.
[Sidenote: Social changes effected by machinery.] While thus the
inventive class of men were gratifying their mental activity, and
following that pursuit which has ever engrossed the energetic in all
ages of the world--the pursuit of riches; for it was quickly perceived
that success in this direction was the high road to wealth, public
consideration, and honour--the realization of riches greater than the
wildest expectations of the alchemists; there were silently and in an
unobserved manner great social and national results arising. The
operative was correct enough in his conclusion that machinery was
throwing him out of work, and reflecting persons were right enough in
their belief that this extensive introduction of machines was in some
way accomplishing a disorganization of the social economy. Doubtless,
for the time being, the distress and misery were very severe; men were
compelled to starve or to turn to new avocations; families were deprived
of their long-accustomed means of support; such must necessarily be the
incidents of every great social change, even though it be a change of
improvement. Nor was it until the new condition of things had passed
through a considerable advance that its political tendency began to be
plainly discerned. It was relieving the labourer from the burden of his
toil, supplanting manual by mechanical action. [Sidenote: Life in the
mill.] In the cotton-mill, which may be looked upon as the embodiment of
the new system and its tendencies, the steam-engine down below was doing
the drudgery, turning the wheels and executing the labour, while the
operatives above--men, women, and children--were engaged in those things
which the engine could not accomplish--things requiring observation and
intelligent action. Under such a state it was not possible but that a
social change should ensue, for relief from corporeal labour is always
followed by a disposition for mental activity; and it was not without a
certain degree of plausibility that the philanthropist, whose attention
was directed to this subject, asserted that the lot of the labouring man
was no better than it had been before: he had changed the tyrant, but
had not got rid of the tyranny; for the demands of the insatiate,
inexorable, untiring steam-engine must be without delay satisfied; the
broken thread must be instantly pieced; the iron fingers must receive
their new supply; the finished work must be forthwith taken away.
[Sidenote: Intellectual activity.] What was thus going on in the mill
was a miniature picture of what was going on in the state. Labour was
comparatively diminishing, mental activity increasing. Throughout the
last century the intellectual advance is most significantly marked, and
surprising is the contrast between the beginning and the close. Ideas
that once had a living force altogether died away, the whole community
offering an exemplification of the fact that the more opportunity men
have for reflection the more they will think. Well, then, might those
whose interests lay in the perpetuation of former ideas and the ancient
order of things look with intolerable apprehension on what was taking
place. They saw plainly that this intellectual activity would at last
find a political expression, and that a power, daily increasing in
intensity, would not fail to make itself felt in the end.
[Sidenote: Difference between past and present ages.] In such things are
manifested the essential differences between the Age of Faith and the
Age of Reason. In the former, if life was enjoyed in calmness it was
enjoyed in stagnation, in unproductiveness, and in a worthless way. But
how different in the latter! Every thing is in movement. So many are the
changes we witness, even in the course of a very brief period, that no
one, though of the largest intellect, or in the most favourable
position, can predict the future of only a few years hence. We see that
ideas which yesterday served us as a guide die to-day, and will be
replaced by others, we know not what, to-morrow.
[Sidenote: Scientific contributions of various nations,] In this
scientific advancement, among the triumphs of which we are living, all
the nations of Europe have been engaged. Some, with a venial pride,
claim for themselves the glory of having taken the lead. But perhaps
each of them, if it might designate the country--alas! not yet a
nation--that should occupy the succeeding post of honour, would inscribe
Italy on its ballot. It was in Italy that Columbus was born; in Venice,
destined one day to be restored to Italy, newspapers were first issued.
It was in Italy that the laws of the descent of bodies to the earth and
of the equilibrium of fluids were first determined by Galileo. In the
Cathedral of Pisa that illustrious philosopher watched the swinging of
the chandelier, and, observing that its vibrations, large and small,
were made in equal times, left the house of God, his prayers unsaid, but
the pendulum clock invented. To the Venetian senators he first showed
the satellites of Jupiter, the crescent form of Venus, and, in the
garden of Cardinal Bandini, the spots upon the sun. [Sidenote:
especially of Italy.] It was in Italy that Sanctorio invented the
thermometer; that Torricelli constructed the barometer and demonstrated
the pressure of the air. It was there that Castelli laid the foundation
of hydraulics and discovered the laws of the flowing of water. There,
too, the first Christian astronomical observatory was established, and
there Stancari counted the number of vibrations of a string emitting
musical notes. There Grimaldi discovered the diffraction of light, and
the Florentine academicians showed that dark heat may be reflected by
mirrors across space. In our own times Melloni furnished the means of
proving that it may be polarized. The first philosophical societies were
the Italian; the first botanical garden was established at Pisa; the
first classification of plants given by Caesalpinus. The first geological
museum was founded at Verona; the first who cultivated the study of
fossil remains were Leonardo da Vinci and Fracasta. The great chemical
discoveries of this century were made by instruments which bear the
names of Galvani and Volta. Why need I speak of science alone? Who will
dispute with that illustrious people the palm of music and painting, of
statuary and architecture? The dark cloud which for a thousand years has
hung over that beautiful peninsula is fringed with irradiations of
light. There is not a department of human knowledge from which Italy has
not extracted glory, no art that she has not adorned.
[Sidenote: Causes of her depression.] Notwithstanding the adverse
circumstances in which she has been placed, Italy has thus taken no
insignificant part in the advancement of science. I may at the close of
a work of which so large a portion has been devoted to the relation of
her influences, political and religious, on the rest of Europe, be
perhaps excused the expression of a hope that the day is approaching in
which she will, with Rome as her capital, take that place in the modern
system to which she is entitled. The course of centuries has proved that
her ecclesiastical relation with foreign countries is incompatible with
her national life. It is that, and that alone, which has been the cause
of all her ills. She has asserted a jurisdiction in every other
government; the price she has paid is her own unity. The first, the
all-important step in her restitution is the reduction of the papacy to
a purely religious element. Her great bishop must no longer be an
earthly prince. Rome, in her outcry for the preservation of her temporal
possessions, forgets that Christian Europe has made a far greater
sacrifice. It has yielded Bethlehem, Gethsemane, Calvary, the Sepulchre,
the Mount of the Ascension. That is a sacrifice to which the surrender
of the fictitious donations of barbarian kings is not to be compared.
* * * * *
The foregoing paragraphs were written in 1859. Since that time Italy
has become a nation, Rome is its capital, Venice belongs to it. In
1870-71 I was an eye-witness of the presence of Italian troops in the
Eternal City.