Worlds in the making - 1908 - Illustrated E-Book

Svante Arrhenius

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• Sprache: Englisch
• Veröffentlichungsjahr: 2022

Beschreibung

When, more than six years ago, I was writing my Treatise of Cosmic Physics, I found myself confronted with great difficulties. The views then held would not explain many phenomena, and they failed in particular in cosmogonic problems. The radiation pressure of light, which had not, so far, been heeded, seemed to give me the key to the elucidation of many obscure problems, and I made a large use of this force in dealing with those phenomena in my treatise.
The explanations which I tentatively offered could, of course, not claim to stand in all their detail; yet the scientific world received them with unusual interest and benevolence. Thus encouraged, I tried to solve more of the numerous important problems, and in the present volume I have added some further sections to the complex of explanatory arguments concerning the evolution of the Universe. The foundation to these explanations was laid in a memoir which I presented to the Academy of Sciences at Stockholm in 1900. The memoir was soon afterwards printed in the Physikalische Zeitschrift, and the subject was further developed in my Treatise of Cosmic Physics.

Leseprobe

WORLDS IN THE MAKING

THE EVOLUTION OF THE UNIVERSE

BYSVANTE ARRHENIUSDIRECTOR OF THE PHYSICO-CHEMICAL NOBEL INSTITUTE, STOCKHOLM

TRANSLATED BY DR. H. BORNS

ILLUSTRATED

1908

© 2022 Librorium Editions

ISBN : 9782383835196

TABLE OF CONTENTS

I.

VOLCANIC PHENOMENA AND EARTHQUAKES

1

Destruction caused by volcanism and by earthquakes.—Different kinds of volcanoes.—Vesuvius.—Products of eruption.—Volcanic activity diminishing.—Structure of volcanoes.—Geographical distribution of volcanoes.—Temperature in the interior of the earth.—Significance of water for volcanism.—Composition of the earth’s interior.—Geographical distribution of earthquakes.—Fissures in the earth’s crust.—Groups of earthquakes.—Waves in the sea and in the air accompanying earthquakes.—Their connection with volcanism.—Systems of fissures.—Seismograms.

II.

THE CELESTIAL BODIES, IN PARTICULAR THE EARTH, AS ABODES OF LIVING BEINGS

39

Manifold character of the worlds.—The earth probably at first a ball of gases.—Formation of the earth crust and its rapid cooling.—Balance between heat received and heat lost by radiation.—Life already existing on the earth for a milliard of years.—The waste of solar heat.—Temperature and habitability of the planets.—Heat-preserving influence of the atmosphere.—Significance of carbon dioxide in the atmosphere.—Warm and cold geological ages.—Fluctuations in the percentage of carbon dioxide of the air.—Combustion, decay, and growth.—Atmospheric oxygen.—Vegetable life more ancient than animal life.—The atmospheres of planets.—Chances of an improvement in the climate.

III.

RADIATION AND CONSTITUTION OF THE SUN

64

Stability of the solar system.—Losses and possible gains of heat by the sun.—Theses of Mayer and of Helmholtz.—Temperatures of the white, yellow, and reddish stars, and of the sun.—Sun-spots and sun faculæ.—Prominences.— Spectra of the parts of the sun.—Temperature of the sun.—The interior of the sun.—Its composition according to the mechanical theory of heat.—The losses of heat by the sun probably covered by the enormous solar energy.

IV.

THE RADIATION PRESSURE

94

Newton’s law of gravitation.—Kepler’s observation of comets’ tails.—The thesis of Euler.—Proof of Maxwell.—The radiation pressure.—Electric charges and condensation.—Comets’ tails and radiation pressure.—Constituents and properties of comets’ tails.—Weight of the solar corona.—Loss and gain of matter by the sun.—Nature of meteorites.—Electric charge of the sun.—Electrons drawn into the sun.—Magnetic properties of the sun and appearance of the corona.—Constituents of the meteors.—Nebulæ and their heat and light.

V.

THE SOLAR DUST IN THE ATMOSPHERE. POLAR LIGHTS AND THE VARIATIONS OF TERRESTRIAL MAGNETISM

118

The supply of dust from the sun rather insignificant.—Polarization of the light of the sky.—The upper clouds.—Different kinds of auroræ.—Their connection with the corona of the sun.—Polar lights and sun-spots.—Periodicity of polar lights.—Polar lights and magnetic disturbances.—Velocity of solar dust.—Fixation of atmospheric nitrogen.—The Zodiacal Light.

VI.

END OF THE SUN.—ORIGIN OF NEBULÆ

148

The extinction of the sun.—Collision between two celestial bodies.—The new star in Perseus.—Formation of nebulæ.—The appearance of nebulæ.—The nebulæ catch wandering meteors and comets.—The ring nebula in Lyra.—Variable stars.—Eta in Argus.—Mira Ceti.—Lyra and Algol stars.—Evolution of the stars.

VII.

THE NEBULAR AND THE SOLAR STATES

191

The energy of the universe.—The entropy of the universe.—The entropy increases in the suns, but decreases in the nebulæ.—Temperature and constitution of the nebulæ.—Schuster’s calculations of the condition of a celestial body consisting of gases.—Action of the loss of heat on nebulæ and on suns.—Development of a rotating nebula into a planetary system.—The hypothesis of Kant-Laplace.—Objections to it.—The views of Chamberlin and Moulton.—The radiation pressure balances the effect of Newtonian gravitation.—The emission of gases from the nebulæ balances the waste of heat characteristic to the solar systems.

VIII.

THE SPREADING OF LIFE THROUGH THE UNIVERSE

212

Stability of the species.—Theory of mutation.—Spontaneous generation.—Bathybius.—Panspermia.—The stand-points of Richter, Ferdinand Cohn, and Lord Kelvin.—The radiation pressure enables spores to escape.—The effect of strong sunlight and of cold on the germinating power.—Transport of spores through the atmosphere into universal space and through it to other planets.—General conclusions.

EXPLANATION OF ABBREVIATIONS, ETC.

The temperatures are stated in degrees centigrade (° C.), either on the Celsius scale, on which the freezing-point of water is 0°, or on the absolute scale, whose zero lies 273 degrees below the freezing-point of water, at -273° C. The equivalent temperatures on the Fahrenheit scale (freezing-point of water 32° F.) are added in brackets (° F.).

Light travels in vacuo at the rate of 300,000 km. (nearly 200,000 miles) per second.

ILLUSTRATIONS

FIG.

1.

VESUVIUS, AS SEEN FROM THE ISLAND OF NISIDA, IN MODERATE ACTIVITY

2.

ERUPTION OF VESUVIUS IN 1882

3.

ERUPTION OF VESUVIUS IN 1872

4.

PHOTOGRAPH OF VESUVIUS, 1906. CHIEFLY CLOUDS OF ASHES

5.

BLOCK LAVA ON MAUNA LOA

6.

THE EXCELSIOR GEYSER IN YELLOWSTONE PARK, U. S. A. REMNANT OF THE POWERFUL VOLCANIC ACTIVITY IN THE TERTIARY AGE

7.

MATO TEPEE IN WYOMING, U. S. A. TYPICAL VOLCANIC"NECK"

8.

CLEFTS FILLED WITH LAVA AND VOLCANIC CONE OF ASHES, TOROWHEAP CAÑON, PLATEAU OF COLORADO

9.

THE KILAUEA CRATER ON HAWAII

10.

CHIEF EARTHQUAKE CENTRES, ACCORDING TO THE BRITISH ASSOCIATION COMMITTEE

11.

CLEFTS IN VALENTIA STREET, SAN FRANCISCO, AFTER THE EARTHQUAKE OF 1906

12.

SAND CRATERS AND FISSURES, PRODUCED BY THE CORINTH EARTHQUAKE OF 1861. IN THE WATER, BRANCHES OF FLOODED TREES

13.

EARTHQUAKE LINES IN LOWER AUSTRIA

14.

LIBERTY BUILDING OF LELAND STANFORD JUNIOR UNIVERSITY, IN CALIFORNIA, AFTER THE EARTHQUAKE OF 1906

15.

EARTHQUAKE LINES IN THE TYRRHENIAN DEPRESSION

16.

SEISMOGRAM RECORDED AT SHIDE, ISLE OF WIGHT, ON AUGUST 31, 1898

17.

PHOTOGRAPH OF THE SURFACE OF THE MOON, IN THE VICINITY OF THE CRATER OF COPERNICUS

18.

SUN-SPOT GROUP AND GRANULATION OF THE SUN

19.

PART OF THE SOLAR SPECTRUM OF JANUARY 3, 1872

20.

METALLIC PROMINENCES IN VORTEX MOTION

21.

FOUNTAIN-LIKE METALLIC PROMINENCES

22.

QUIET PROMINENCES OF SMOKE-COLUMN TYPE

23.

QUIET PROMINENCES, SHAPE OF A TREE

24.

DIAGRAM ILLUSTRATING THE DIFFERENCES IN THE SPECTRA OF SUN-SPOTS AND OF THE PHOTOSPHERE

25.

SPECTRUM OF A SUN-SPOT, THE CENTRAL BAND BETWEEN THE TWO PORTIONS OF THE PHOTOSPHERE SPECTRUM

26.

THE GREAT SUN-SPOT OF OCTOBER 9, 1903

27.

THE GREAT SUN-SPOT OF OCTOBER 9, 1903

28.

THE GREAT SUN-SPOT OF OCTOBER 9, 1903

29.

THE GREAT SUN-SPOT OF OCTOBER 9, 1903

30.

PHOTOGRAPH OF THE SOLAR CORONA OF 1900

31.

PHOTOGRAPH OF THE SOLAR CORONA OF 1870

32.

PHOTOGRAPH OF THE SOLAR CORONA OF 1898

33.

PHOTOGRAPH OF ROERDAM’S COMET (1893 II.), SUGGESTING SEVERAL STRONG NUCLEI IN THE TAIL

34.

PHOTOGRAPH OF SWIFT’S COMET (1892 I.)

35.

DONATI’S COMET AT ITS GREATEST BRILLIANCY IN 1858

36.

IMITATION OF COMETS’ TAILS

37.

GRANULAR CHONDRUM FROM THE METEORITE OF SEXES. ENLARGEMENT 1 : 70

38.

ARCH-SHAPED AURORÆ BOREALIS, OBSERVED BY NORDENSKIOLD DURING THE WINTERING OF THE VEGA IN BERING STRAIT 1879

39.

AURORA BOREALIS, WITH RADIAL STREAMERS

40.

AURORA WITH CORONA, OBSERVED BY GYLLENSKIÖLD ON SPITZBERGEN, 1883

41.

POLAR-LIGHT DRAPERIES, OBSERVED IN FINNMARKEN, NORTHERN NORWAY

42.

CURVE OF MAGNETIC DECLINATION AT KEW, NEAR LONDON, ON NOVEMBER 15 AND 16, 1905

43.

CURVE OF HORIZONTAL INTENSITY AT KEW ON NOVEMBER 15 AND 16, 1905

44.

ZODIACAL LIGHT IN THE TROPICS

45.

SPECTRUM OF NOVA AURIGÆ, 1892

46.

DIAGRAM INDICATING THE CONSEQUENCES OF A COLLISION BETWEEN TWO EXTINCT SUNS

47.

SPIRAL NEBULA IN THE CANES VENATICI

48.

SPIRAL NEBULA IN THE TRIANGLE

49.

THE GREAT NEBULA IN ANDROMEDA

50.

RING-SHAPED NEBULA IN LYRA

51.

CENTRAL PORTION OF THE GREAT NEBULA IN ORION

52.

NEBULAR STRIÆ IN THE STARS OF THE PLEIADES

53.

NEBULAR STRIÆ IN THE SWAN

54.

NEBULA AND STAR RIFT IN THE SWAN, IN THE MILKY WAY

55.

GREAT NEBULA NEAR RHO, IN OPHIUCHUS

56.

STAR CLUSTER IN HERCULES

57.

STAR CLUSTER IN PEGASUS

58.

CONE-SHAPED STAR CLUSTER IN GEMINI

59.

COMPARISON OF SPECTRA OF STARS OF CLASSES 2, 3, 4

60.

COMPARISON OF SPECTRA OF STARS OF CLASSES 2, 3, 4

PREFACE

When, more than six years ago, I was writing my Treatise of Cosmic Physics, I found myself confronted with great difficulties. The views then held would not explain many phenomena, and they failed in particular in cosmogonic problems. The radiation pressure of light, which had not, so far, been heeded, seemed to give me the key to the elucidation of many obscure problems, and I made a large use of this force in dealing with those phenomena in my treatise.

The explanations which I tentatively offered could, of course, not claim to stand in all their detail; yet the scientific world received them with unusual interest and benevolence. Thus encouraged, I tried to solve more of the numerous important problems, and in the present volume I have added some further sections to the complex of explanatory arguments concerning the evolution of the Universe. The foundation to these explanations was laid in a memoir which I presented to the Academy of Sciences at Stockholm in 1900. The memoir was soon afterwards printed in the Physikalische Zeitschrift, and the subject was further developed in my Treatise of Cosmic Physics.

It will be objected, and not without justification, that scientific theses should first be discussed and approved of in competent circles before they are placed before the public. It cannot be denied that, if this condition were to be fulfilled, most of the suggestions on cosmogony that have been published would never have been sent to the compositors; nor do I deny that the labor spent upon their publication might have been employed for some better purpose. But several years have elapsed since my first attempts in this direction were communicated to scientists. My suggestions have met with a favorable reception, and I have, during these years, had ample opportunity carefully to re-examine and to amend my explanations. I therefore feel justified in submitting my views to a larger circle of readers.

The problem of the evolution of the Universe has always excited the profound interest of thinking men. And it will, without doubt, remain the most eminent among all the questions which do not have any direct, practical bearing. Different ages have arrived at different solutions to this great problem. Each of these solutions reflected the stand-point of the natural philosophers of its time. Let me hope that the considerations which I offer will be worthy of the grand progress in physics and chemistry that has marked the close of the nineteenth and the opening of the twentieth century.

Before the indestructibility of energy was understood, cosmogony merely dealt with the question how matter could have been arranged in such a manner as to give rise to the actual worlds. The most remarkable conception of this kind we find in Herschel’s suggestion of the evolution of stellar nebulæ, and in the thesis of Laplace concerning the formation of the solar system out of the universal nebula. Observations more and more tend to confirm Herschel’s view. The thesis of Laplace, for a long time eulogized as the flower of cosmogonic speculations, has more and more had to be modified. If we attempt, with Kant, to conceive how wonderfully organized stellar systems could originate from absolute chaos, we shall have to admit that we are attacking a problem which is insoluble in that shape. There is a contradiction in those very attempts to explain the origin of the Universe in its totality, as Stallo[1] emphasizes: "The only question to which a series of phenomena gives legitimate rise relates to their filiation and interdependence." I have, therefore, only endeavored to show how nebulæ may originate from suns and suns from nebulæ; and I assume that this change has always been proceeding as it is now.

The recognition of the indestructibility of energy seemed to accentuate the difficulties of the cosmogonic problems. The theses of Mayer and of Helmholtz, on the manner in which the Sun replenishes its losses of heat, have had to be abandoned. My explanation is based upon chemical reactions in the interior of the Sun in accordance with the second law of thermodynamics. The theory of the "degradation" of energy appeared to introduce a still greater difficulty. That theory seems to lead to the inevitable conclusion that the Universe is tending towards the state which Clausius has designated as "Wärme Tod" (heat death), when all the energy of the Universe will uniformly be distributed through space in the shape of movements of the smallest particles. That would imply an absolutely inconceivable end of the development of the Universe. The way out of this difficulty which I propose comes to this: the energy is "degraded" in bodies which are in the solar state, and the energy is "elevated," raised to a higher level, in bodies which are in the nebular state.

Finally, I wish to touch upon one cosmogonical question which has recently become more actual than it used to be. Some kind of "spontaneous generation," origination of life from inorganic matter, had been acquiesced in. But just as the dreams of a spontaneous generation of energy—i.e., of a perpetuum mobile—have been dispelled by the negative results of all experiments in that direction, just in the same way we shall have to give up the idea of a spontaneous generation of life after all the repeated disappointments in this field of investigation. As Helmholtz[2] says, in his popular lecture on the growth of the planetary system (1871): "It seems to me a perfectly just scientific procedure, if we, after the failure of all our attempts to produce organisms from lifeless matter, put the question, whether life has had a beginning at all, or whether it is not as old as matter, and whether seeds have not been carried from one planet to another and have developed everywhere where they have fallen on a fertile soil."

This hypothesis is called the hypothesis of panspermia, which I have modified by combining it with the thesis of the radiation pressure.

My guiding principle in this exposition of cosmogonic problems has been the conviction that the Universe in its essence has always been what it is now. Matter, energy, and life have only varied as to shape and position in space.

The Author.

Stockholm, December, 1907.

WORLDS IN THE MAKING

IVOLCANIC PHENOMENA AND EARTHQUAKES

The Interior of the Earth

The disasters which have recently befallen the flourishing settlements near Vesuvius and in California have once more directed the attention of mankind to the terrific forces which manifest themselves by volcanic eruptions and earthquakes.

The losses of life which have been caused in these two last instances are, however, insignificant by comparison with those which various previous catastrophes of this kind have produced. The most violent volcanic eruption of modern times is no doubt that of August 26 and 27, 1883, by which two-thirds of the island of Krakatoa, 33 square kilometres (13 square miles) in area, situated in the East Indian Archipelago, were blown into the air. Although this island was itself uninhabited, some 40,000 people perished on that occasion, chiefly by the ocean wave which followed the eruption and which caused disastrous inundations in the district. Still more terrible was the destruction wrought by the Calabrian earthquake of February and March, 1783, which consisted of several earthquake waves. The large town of Messina was destroyed on February 5th, and the number of people killed by this event has been estimated at 100,000. The same region, especially Calabria, has, moreover, frequently been visited by disastrous earthquakes—again in 1905 and 1907. Another catastrophe upon which history dwells, owing to the loss of life (not less than 90,000), was the destruction of the capital of Portugal on November 1, 1755. Two-thirds of the human lives which this earthquake claimed were destroyed by a wave 5 m. in height rushing in from the sea.

Fig. 1.—Vesuvius, as seen from the Island of Nisida, in moderate activity

Vesuvius is undoubtedly the best studied of all volcanoes. During the splendor of Rome this mountain was quite peaceful—known as an extinct volcanic cone so far as history could be traced back. On the extraordinarily fertile soil about it had arisen big colonies of such wealth that the district was called Great Greece (Græcia Magna). Then came, in the year 79 A.D., the devastating eruption which destroyed, among others, the towns of Herculaneum and Pompeii. The volumes of gas, rushing forth with extreme violence from the interior of the earth, pushed aside a large part of the volcanic cone whose remnant is now called Monte Somma, and the falling masses of ashes, mixed with streams of lava, built up the new Vesuvius. This mountain has repeatedly changed its appearance during later eruptions, and was provided with a new cone of ashes in the year 1906. The outbreak of the year 79 was succeeded by new eruptions in the years 203, 472, 512, 685, 993, 1036, 1139, 1500, 1631, and 1660, at quite irregular intervals. Since that time Vesuvius has been in almost uninterrupted activity, mostly, however, of a harmless kind, so that only the cloud of smoke over its crater indicated that the internal glow was not yet extinguished. Very violent eruptions took place in the years 1794, 1822, 1872, and 1906.

Other volcanoes behave quite differently from these violent volcanoes, and do hardly any noteworthy damage. Among these is the crater-island of Stromboli, situated between Sicily and Calabria. This volcano has been in continuous activity for thousands of years. Its eruptions succeed one another at intervals ranging from one minute to twenty minutes, and its fire serves the sailors as a natural light-house. The force of this volcano is, of course, unequal at different periods. In the summer of 1906 it is said to have been in unusually violent activity. Very quiet, as a rule, are the eruptions of the great volcanoes on Hawaii.

Foremost among the substances which are ejected from volcanoes is water vapor. The cloud floating above the crater is, for this reason, the surest criterion of the activity of the volcano. Violent eruptions drive the masses of steam up into the air to heights of 8 km. (5 miles), as the illustrations (Figs. 1 to 4) will show.

The height of the cloud may be judged from the height of Vesuvius, 1300 metres (nearly 4300 ft.) above sea-level. The illustration on page 4 (Fig. 2) is a reproduction of a drawing by Poulett Scrope, representing the Vesuvius eruption of the year 1822. There seems to have been no wind on this day; the masses of steam formed a cloud of a regular shape which reminds us of a pine-tree. According to the description of Plinius, the cloud noticed at the eruption of Vesuvius in the year 79 must have been of the same kind. When the air is not so calm the cloud assumes a more irregular shape (Fig. 3). Clouds which rise to such elevations as we have spoken of are distinguished by strong electric charges. The vivid flashes of lightning which shoot out of the black clouds add to the terror of the awful spectacle.

Fig. 2.—Eruption of Vesuvius in 1882. (After a contemporaneous drawing by Poulett Scrope)

The rain which pours down from this cloud is often mixed with ashes and is as black as ink. The ashes have a color which varies between light-gray, yellow-gray, brown, and almost black, and they consist of minute spherules of lava ejected by the force of the gases and rapidly congealed by contact with the air. Larger drops of lava harden to volcanic sand—the so-called "lapilli" (that is, little stones), or to "bombs," which are often furrowed by the resistance offered by the air, and turn pear-shaped. These solid products, as a rule, cause the greatest damage due to volcanic eruptions. In the year 1906 the weight of these falling masses (Fig. 4) crushed in the roofs of houses. A layer of ashes 7 m. (23 ft.) in thickness buried Pompeii under a protective crust which had covered it up to days of modern excavations. The fine ashes and the muddy rain clung like a mould of plaster to the dead bodies. The mud hardened afterwards into a kind of cement, and as the decomposition products of the dead bodies were washed away, the moulds have provided us with faithful casts of the objects that had once been embedded in them. When the ashes fall into the sea, a layer of volcanic tuffa is formed in a similar manner, which enshrines the animals of the sea and algæ. Of this kind is the soil of the Campagna Felice, near Naples. Larger lumps of solid stones with innumerable bubbles of gases float as pumice-stone on the sea, and are gradually ground down into volcanic sand by the action of the waves. The floating pumice-stone has sometimes become dangerous or, at any rate, an obstacle to shipping, through its large masses; that was, at least, the case with the Krakatoa eruption of 1883.

Fig. 3.—Eruption of Vesuvius in 1872. (After a photograph.)

Among the gases which are ejected in addition to water vapor, carbonic acid should be mentioned in the first instance; also vapors of sulphur and sulphuretted hydrogen, hydrochloric acid, and chloride of ammonium, as well as the chlorides of iron and copper, boric acid, and other substances. A large portion of these bodies is precipitated on the edges of the volcano, owing to the sudden cooling of the gases. The more volatile constituents, such as carbonic acid, sulphuretted hydrogen, and hydrochloric acid, may spread over large areas, and destroy all living beings by their heat and poison. It was these gases, for example, which caused the awful devastation at St. Pierre, where 30,000 human lives were destroyed on May 8, 1902, by the eruption of Mont Pelée. The ejection of hydrogen gas, which, on emerging from the lava, is burned to water by the oxygen of the air, has been observed in the crater of Kilauea.

The ashes of the volcanoes are sometimes carried to vast distances by the air currents—e.g., from the western coast of South America to the Antilles; from Iceland to Norway and Sweden; from Vesuvius (1906) to Holstein. Best known in this respect is the eruption of the Krakatoa, which drove the fine ashes up to an elevation of 30 km. (18 miles). The finest particles of these ashes were slowly carried by the winds to all parts of the earth, where they caused, during the following two years, the magnificent sunrises and sunsets which were spoken of as "the red glows." This glow was also observed in Europe after the eruption of Mont Pelée. The dust of Krakatoa further supplied the material for the so-called "luminous clouds of the night," which were seen in the years 1883 to 1892 floating at an elevation of about 80 km. (50 miles), and hence illuminated by the light of the sun long after sunset.

The crater of Kilauea, on the high volcano of Mauna Loa, in Hawaii—this volcano is about of the same height as Mont Blanc—has excited special interest. The crater forms a large lake of lava having an area of about 12 sq. km. (nearly 5 sq. miles), which, however, varies considerably with time. The lava boiling at red glow is constantly emitting masses of gas under slight explosions, spurting out fiery fountains to a height of 20 m. (65 ft.) into the air. Here and there lava flows out from crevices in the wall of the crater down the slope of the mountain, until the surface of the lake of lava has descended below these cracks. As a rule, this lava is of a thin fluid consistency, and it spreads, therefore, rather uniformly over large areas. Of a similar kind are also the floods of lava which are sometimes poured over thousands of square kilometres on Iceland. The so-called Laki eruption of the year 1783 was of a specially grand nature. Though occurring in an uninhabited district, it did a great amount of damage. In the more ancient geological periods, especially in the Tertiary age, similar sheets of lava of vast extensions have been spread over England and Scotland (more than 100,000 sq. km., roughly, 40,000 sq. miles); over Deccan, in India, 400,000 sq. kms. (150,000 sq. miles), up to heights of 2000 m. (6500 ft.); and over Wyoming, Yellowstone Park, Nevada, Utah, Oregon, and other districts of the United States, as well as over British Columbia.

Fig. 4.—Photograph of Vesuvius, 1906. Chiefly clouds of ashes

In other cases the slowly ejected lava is charged with large volumes of gases, which escape when the lava congeals and burst it up into rough, unequal blocks, forming the so-called block lava (Fig. 5). The streams of lava can likewise produce terrible devastation when they descend into inhabited districts; on account of their slow motion, they rarely cause loss of life, however.

Where the volcanic activity gradually lessens or ceases, we can still trace it by the exhalations of gas and the springs of warm water which we find in many districts where, during the Tertiary age, powerful volcanoes were ejecting their streams of lava. To this class belong the famous geysers of Iceland, of Yellowstone Park (Fig. 6), and of New Zealand; also the hot springs of Bohemia, so highly valued therapeutically (e.g., the Karlsbad Sprudel); the Fumaroli of Italy, Greece, and other countries, exhaling water vapor; the Mofettæ, with their exhalations of carbonic acid (of frequent occurrence in the district of the Eifel and on both sides of the middle Rhine, in the Dogs Grotto near Naples, and in the Valley of Death in Java); the Solfatara, exhaling vapors of sulphur—sulphuretted hydrogen and sulphur dioxide (they are found near Naples on the Phlegræan Fields and in Greece); as well as many of the so-called mud volcanoes, which eject mud, salt water, and gases (as a rule, carbonic acid and hydrocarbons)—for example, the mud volcanoes near Parma and Modena, in Italy, and those near Kronstadt, in Transylvania.

Fig. 5.—Block lava on Mauna Loa

The extinct volcanoes, of which some, like the Aconcagua, 6970 m. (22,870 ft.), in South America, and the Kilimanjaro, in Africa, 6010 m. (19,750 ft.), rank among the highest mountains, are exposed to a rapid destruction by the rain, because they consist largely of loose materials—volcanic ashes with interposed layers of lava. Where these lava streams expand gradually, they protect the ground underneath from erosion by water, and in this way proper cuts are formed on the edges of the lava streams, passing through the old volcano and through the sedimentary strata at deeper levels.

Fig. 6.—The Excelsior Geyser in Yellowstone Park, U. S. A. Remnant of powerful volcanic activity in the Tertiary age

The old volcano of Monte Venda, near Padua, affords an interesting example of this type. We can observe there how the sedimentary limestone has been changed by the lava, which was flowing over it, into marble to a depth of about 1 m. (3 ft.) Sometimes the limestone which is lying over the lava has also undergone the same transformation, which would indicate that lava has not only been flowing above the edge of the crater, but has also forced itself out on the sides through the fissures between two layers of limestone. Massive subterranean lava streams of this kind are found in the so-called lakkolithes of Utah and in the Caucasus. There the superior layers have been forced upward by the lava pressing from below; the lava froze, however, before it reached the surface of the earth, where it might have formed a volcano. Quite a number of granites, the so-called batholithes, chiefly occurring in Norway, Scotland, and Java, are of similar origin. Occasionally it is only the core of congealed lava that has remained of the whole volcano. These cores, which originally filled the pipe of the crater, are frequent in Scotland and in North America, where they are designated "necks" (Fig. 7).