Chapter I: Part 1

Transcriber’s Notes

Obvious typographical errors have been silently corrected. Variations in hyphenation have been standardised but all other spelling and punctuation remains unchanged.

Italics are represented thus _italic_, bold thus =bold= and superscripts thus y^{en}.

WORLDS
IN THE MAKING

THE EVOLUTION OF THE UNIVERSE

BY
SVANTE ARRHENIUS

DIRECTOR OF THE PHYSICO-CHEMICAL NOBEL
INSTITUTE, STOCKHOLM

TRANSLATED BY
DR. H. BORNS

ILLUSTRATED

[colophon]

NEW YORK AND LONDON
HARPER & BROTHERS PUBLISHERS
MCMVIII

Copyright, 1908, by HARPER & BROTHERS.

_All rights reserved._

Published March, 1908.

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.).

1 metre (m.) = 10 decimetres (dm.) = 100 centimetres (cm.) = 1000 millimetres (mm.) = 3.28 ft.; 1 kilometre (km.) = 1000 metres (m.) = 0.62 miles; 1 mile = 1.6 kilometres (km.).

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

ILLUSTRATIONS

FIG. PAGE

1. VESUVIUS, AS SEEN FROM THE ISLAND OF NISIDA, IN
MODERATE ACTIVITY 2

2. ERUPTION OF VESUVIUS IN 1882 4

3. ERUPTION OF VESUVIUS IN 1872 6

4. PHOTOGRAPH OF VESUVIUS, 1906. CHIEFLY CLOUDS OF
ASHES 8

5. BLOCK LAVA ON MAUNA LOA 10

6. THE EXCELSIOR GEYSER IN YELLOWSTONE PARK, U. S. A.
REMNANT OF THE POWERFUL VOLCANIC ACTIVITY IN THE
TERTIARY AGE 11

7. MATO TEPEE IN WYOMING, U. S. A. TYPICAL VOLCANIC
“NECK” 12

8. CLEFTS FILLED WITH LAVA AND VOLCANIC CONE OF ASHES,
TOROWHEAP CAÑON, PLATEAU OF COLORADO 13

9. THE KILAUEA CRATER ON HAWAII 15

10. CHIEF EARTHQUAKE CENTRES, ACCORDING TO THE BRITISH
ASSOCIATION COMMITTEE 22

11. CLEFTS IN VALENTIA STREET, SAN FRANCISCO, AFTER THE
EARTHQUAKE OF 1906 25

12. SAND CRATERS AND FISSURES, PRODUCED BY THE CORINTH
EARTHQUAKE OF 1861. IN THE WATER, BRANCHES OF
FLOODED TREES 27

13. EARTHQUAKE LINES IN LOWER AUSTRIA 30

14. LIBERTY BUILDING OF LELAND STANFORD JUNIOR UNIVERSITY,
IN CALIFORNIA, AFTER THE EARTHQUAKE OF 1906 32

15. EARTHQUAKE LINES IN THE TYRRHENIAN DEPRESSION 34

16. SEISMOGRAM RECORDED AT SHIDE, ISLE OF WIGHT, ON
AUGUST 31, 1898 35

17. PHOTOGRAPH OF THE SURFACE OF THE MOON, IN THE VICINITY
OF THE CRATER OF COPERNICUS 62

18. SUN-SPOT GROUP AND GRANULATION OF THE SUN 74

19. PART OF THE SOLAR SPECTRUM OF JANUARY 3, 1872 75

20. METALLIC PROMINENCES IN VORTEX MOTION 76

21. FOUNTAIN-LIKE METALLIC PROMINENCES 76

22. QUIET PROMINENCES OF SMOKE-COLUMN TYPE 77

23. QUIET PROMINENCES, SHAPE OF A TREE 77

24. DIAGRAM ILLUSTRATING THE DIFFERENCES IN THE SPECTRA
OF SUN-SPOTS AND OF THE PHOTOSPHERE 78

25. SPECTRUM OF A SUN-SPOT, THE CENTRAL BAND BETWEEN
THE TWO PORTIONS OF THE PHOTOSPHERE SPECTRUM 78

26. THE GREAT SUN-SPOT OF OCTOBER 9, 1903 79

27. THE GREAT SUN-SPOT OF OCTOBER 9, 1903 80

28. THE GREAT SUN-SPOT OF OCTOBER 9, 1903 81

29. THE GREAT SUN-SPOT OF OCTOBER 9, 1903 82

30. PHOTOGRAPH OF THE SOLAR CORONA OF 1900 83

31. PHOTOGRAPH OF THE SOLAR CORONA OF 1870 84

32. PHOTOGRAPH OF THE SOLAR CORONA OF 1898 85

33. PHOTOGRAPH OF ROERDAM’S COMET (1893 II.), SUGGESTING
SEVERAL STRONG NUCLEI IN THE TAIL 100

34. PHOTOGRAPH OF SWIFT’S COMET (1892 I.) 101

35. DONATI’S COMET AT ITS GREATEST BRILLIANCY IN 1858 102

36. IMITATION OF COMETS’ TAILS 104

37. GRANULAR CHONDRUM FROM THE METEORITE OF SEXES.
ENLARGEMENT 1:70 109

38. ARCH-SHAPED AURORÆ BOREALIS, OBSERVED BY NORDENSKIOLD
DURING THE WINTERING OF THE VEGA IN
BERING STRAIT 1879 124

39. AURORA BOREALIS, WITH RADIAL STREAMERS 125

40. AURORA WITH CORONA, OBSERVED BY GYLLENSKIÖLD ON
SPITZBERGEN, 1883 126

41. POLAR-LIGHT DRAPERIES, OBSERVED IN FINNMARKEN, NORTHERN
NORWAY 127

42. CURVE OF MAGNETIC DECLINATION AT KEW, NEAR LONDON,
ON NOVEMBER 15 AND 16, 1905 138

43. CURVE OF HORIZONTAL INTENSITY AT KEW ON NOVEMBER
15 AND 16, 1905 139

44. ZODIACAL LIGHT IN THE TROPICS 146

45. SPECTRUM OF NOVA AURIGÆ, 1892 154

46. DIAGRAM INDICATING THE CONSEQUENCES OF A COLLISION
BETWEEN TWO EXTINCT SUNS 157

47. SPIRAL NEBULA IN THE CANES VENATICI 159

48. SPIRAL NEBULA IN THE TRIANGLE 161

49. THE GREAT NEBULA IN ANDROMEDA 163

50. RING-SHAPED NEBULA IN LYRA 164

51. CENTRAL PORTION OF THE GREAT NEBULA IN ORION 165

52. NEBULAR STRIÆ IN THE STARS OF THE PLEIADES 167

53. NEBULAR STRIÆ IN THE SWAN 169

54. NEBULA AND STAR RIFT IN THE SWAN, IN THE MILKY WAY 171

55. GREAT NEBULA NEAR RHO, IN OPHIUCHUS 172

56. STAR CLUSTER IN HERCULES 173

57. STAR CLUSTER IN PEGASUS 175

58. CONE-SHAPED STAR CLUSTER IN GEMINI 176

59. COMPARISON OF SPECTRA OF STARS OF CLASSES 2, 3, 4 185

60. COMPARISON OF SPECTRA OF STARS OF CLASSES 2, 3, 4 186

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.

[Footnote 1: Stallo: _Concepts and Theories of Modern Physics_.
London, 1900, p. 276.]

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.”

[Footnote 2: Helmholtz, _Populäré Wissenschaftliche Vorträge_.
Braunschweig, 1876, vol. iii., p. 101.]

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

I

VOLCANIC 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.

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.

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.

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.

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.

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.

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).

The so-called cañons of the Colorado Plateau, with their almost vertical walls, are the results of the erosive action of rivers. A drawing by Dutton shows a wall of this kind more than 800 m. (2600 ft.) in height, through four fissures of which lava streams have forced their way up to the surface (Fig. 8). Over one of these fissures a small cone of volcanic ashes is still visible, while the cones which probably overtopped the three other fissures have been washed away, so that the veins end in small “necks.” Evidently a very fluid lava—strong percentages of magnesia and of oxide of iron render the lava more fluid than an admixture of silicic acid, and the fluidity is further increased by the presence of water—has been forced into the fissures which were already present, and has reached the surface of the earth before it froze. The driving force behind them must have been pretty strong; else the lava streams could not have attained the necessary velocity of flow.

When the Krakatoa was blown into the air in 1883 half of the volcano remained behind. This half clearly shows the section of the cone of ashes, which has been but very slightly affected by the destructive action of the water. We find there in the central part the light-colored stopper of lava in the volcano pipe, and issuing from it more light-colored beds of lava, between which darker strata of ashes can be seen.

The distribution of volcanoes over the surface of the earth is marked by striking regularities. Almost all the volcanoes are situated near the shores of the sea. A few are found in the interior of East Africa; but they are, at any rate, near the Great Lakes of the equatorial regions. The few volcanoes which are supposed to be situated in Central Asia must be regarded as doubtful. We miss, however, volcanoes on some sea-coasts, as in Australia and along the long coast-lines of the Northern Arctic Ocean to the north of Asia, Europe, and America. Volcanoes occur only where great cracks occur in the crust of the earth along the sea-coast. Where such fissures are found, but where the sea or large inland lake basins are not near—as, for instance, in the Austrian Alps—we do not meet with any volcanoes; such districts are, however, renowned for their earthquakes.

Since ancient ages the belief has been entertained that the molten masses of the interior of the earth find an outlet through the volcanoes. Attempts have been made to estimate the depth of the hearths of volcanoes, but very different values have been deduced. Thus, the hearth under the volcano of Monte Nuovo, which was thrown up in the year 1538 on the Phlegræan Fields, near Naples, has been credited with depths varying from 1.3 km. to 60 km. (1 mile to 40 miles); for the Krakatoa, estimates of more than 50 km. (30 miles) have been made. All these calculations are rather aimless; for the volcanoes are probably situated on folds of the earth-crust, through which the fluid mass (the magma) rushes forth in wedges from the interior of the earth, and it will presumably be very difficult to say where the hearth of magma ends and where the volcanic pipe commences. The Kilauea gives the visitor the impression that he is standing over an opening in the crust of the earth, through which the molten mass rushes forth directly from the interior of the earth. (Fig. 9.)

As regards the earth-crust, we know from observations in bore-holes made in different parts of the world that the temperature increases rather rapidly with the depth, on an average by about thirty degrees Cent. per kilometre (about 1.6° F. per 100 feet). It must be remarked, however, that the depth of our deepest bore-holes hardly exceeds 2 km. (Paruchowitz, in Silesia, 2003 m., or 6570 ft.; Schladebach, near Merseburg, Prussian Saxony, 1720 m.). If the temperature should go on increasing at the rate of 30 degrees Cent. for each further kilometre, the temperature at a depth of 40 kilometres should attain degrees at which all the common rocks would melt. But the melting-point certainly rises at the same time as the pressure. The importance of this circumstance was, however, much exaggerated when it was believed that for this reason the interior of the earth might possibly be solid. Tammann has shown by direct experiments that the temperature of fusion only rises up to a certain pressure, and that it begins to decrease again on a further increase of pressure. The depths indicated above are therefore not quite correct. If we assume, however, that other kinds of rock behave like diabase—the melting-point of which, according to the determinations of Barus, rises by 1° Cent. for each 40 atmospheres of pressure corresponding to a depth of 155 m.—we should conclude that the solid crust of the earth could not have a greater thickness than 50 or 60 km. (40 miles). At greater depths we should therefore penetrate into the fused mass. On account of its smaller density the silicic acid will be concentrated in the upper strata of the molten mass, while the basic portions of the magma, which are richer in iron oxide, will collect in the lower strata, owing to their greater density.

This magma we have to picture to ourselves as an extremely viscid liquid resembling asphalt. The experiments of Day and Allen show that rods, supported at their ends, of 30 × 2 × 1 mm. of different minerals, like the feldspars microcline and albite, could retain their shape for three hours without curving noticeably, although their temperature was about a hundred degrees above their melting-point, and although they appeared completely fused, or, more correctly, completely vitrified when taken out of the furnace. These molten silicates behave very differently from other liquids like water and mercury, with which we are more accustomed to deal.

The motion and diffusion in the magma, and especially in the very viscous and sluggish acid portions of the upper strata, will therefore be exceedingly small, and the magma will behave almost like a solid body, like the minerals of the experiments of Day and Allen. The magmas of volcanoes like Etna, Vesuvius, and Pantellaria may, therefore, have quite different compositions, as we should conclude from their lavas without our being forced to believe, with Stübel, that these three hearths of volcanoes are completely separated, though not far removed from one another. In the lava of Vesuvius a temperature of 1000 or 1100 degrees has been found at the lower extremity of the stream. From the occurrence in the lava of certain crystals like leucite and olivin, which we have reason to assume must have been formed before the lava left the crater, it has been concluded that the lava temperature cannot have been higher than 1400 degrees before it left the volcanic pipe.

It would, however, be erroneous to deduce from the temperature of the lava of Vesuvius that the hearth of the volcano must be situated at a depth of approximately 50 kilometres. Most likely its depth is much smaller, perhaps not even 10 kilometres. For there, as everywhere where volcanoes occur, the crust of the earth is strongly furrowed, and the magma will just at the spots where we find volcanoes come much nearer to the surface of the earth than elsewhere.

The importance of water for the formation of volcanoes probably lies in the fact that, in the neighborhood of cracks under the bottom of the sea, the water penetrates down to considerable depths. When the water reaches a stratum of a temperature of 365 degrees—the so-called critical temperature of water—it can no longer remain in the liquid state. That would not prevent, however, its penetrating still farther into the depths, in spite of its gaseous condition. As soon as the vapor comes in contact with magma, it will eagerly be absorbed by the magma. The reason is that water of a temperature of more than 300 degrees is a stronger acid than silicic acid; the latter is therefore expelled by it from its compounds, the silicates, which form the main constituents of the magma. The higher the temperature, the greater the power of the magma to absorb water. Owing to this absorption the magma swells and becomes at the same time more fluid. The magma is therefore pressed out by the action of a pressure which is analogous to the osmotic pressure by virtue of which water penetrates through a membrane into a solution of sugar or salt. This pressure may become equivalent to thousands of atmospheres, and this very pressure would raise the magma up the volcanic pipe even to a height of 6000 m. (20,000 feet) above the sea-level. As the magma is ascending in the volcanic pipe it is slowly cooled, and its capacity for binding water diminishes with falling temperature. The water will hence escape under violent ebullition, tearing drops and larger lumps of lava with it, which fall down again as ashes or pumice-stone. After the lava has flown out of the crater and is slowly cooling, it continues to give off water, breaking up under the formation of block lava (see Fig. 5). If, on the other hand, the lava in the crater of the volcano is comparatively at rest, as in Kilauea, the water will escape more slowly; owing to the long-continued contact of the surface layer of lava with the air, little water will remain in it, the water being, so to say, removed by aeration, and the lava streams will therefore, when congealing, form more smooth surfaces.

In some cases volcanoes have been proved (Stübel and Branco) not to be in connection with any fractures in the crust of the earth. That holds, for instance, for several volcanoes of the early Tertiary age in Swabia. We may imagine that the pressure produced by the swelling of the magma became so powerful as to be able to break through the earth-crust at thinner spots, even in the absence of previous fissures.

If, in our consideration, we follow the magma farther into the depths, we shall not find any reason for assuming that the temperature will not rise farther towards the interior of the earth. At depths of 300 or 400 km. (250 miles) the temperature must finally attain degrees such that no substance will be able to exist in any other state than the gaseous. Within this layer the interior of the earth must, therefore, be gaseous. From our knowledge of the behavior of gases at high temperatures and pressures, we may safely conclude that the gases in the central portions of the earth will behave almost like an extremely viscid magma. In certain respects they may probably be compared to solid bodies; their compressibility, in particular, will be very small.

We might think that we could not possibly learn anything concerning the condition of those strata. Earthquakes have, however, supplied us with a little information. Such gaseous masses must fill by far the greatest part of the earth, and they must have a very high specific gravity; for the average density of the earth is 5.52, and the outer strata, the ocean and the masses of the surface which are known to us, have smaller densities. The ordinary rocks possess a density ranging from 2.5 to 3. It must, therefore, be assumed that the materials of the innermost portions of the earth must be metallic, and Wiechert, in particular, has advocated this view. Iron will presumably form the chief constituent of this gas of the central earth. Spectrum analysis teaches us that iron is a very important constituent of the sun. We know, further, that the metallic portions of the meteorites consist essentially of iron; and finally terrestrial magnetism indicates that there must be large masses of iron in the interior of the earth. We have also reason to believe that the native iron occurring in nature—_e.g._, the well-known iron of Ovifak, in Greenland—is of volcanic origin. The materials in the gaseous interior of the earth will, owing to their high density, behave in chemical and physical respects like liquids. As substances like iron will, also at very high temperatures, have a far higher specific gravity than their oxides, and these again have a higher gravity than their silicates, we have to assume that the gases in the core of the earth will almost exclusively be metallic, that the outer portions of the core will contain essentially oxides, and those farther out again mostly silicates.

The fused magma will, on penetrating in the shape of batholithes into the upper layers, probably be divided into two portions, of which one, the lighter and gaseous, will contain water and substances soluble in it; while the other, heavier portion, will essentially consist of silicates with a lower percentage of water. The more fluid portion, richer in water, will be secreted in the higher layers, will penetrate into the surrounding sedimentary strata, especially into their fissures, and will fill them with large crystals, often of metallurgical value—_e.g._, of the ores of tin, copper, and other metals, while the water will slowly evaporate through the superposed strata. The more viscid and sluggish mass of silicates, on the other hand, will congeal, thanks to its great viscosity, to glass, or, when the cooling is very slow, to small crystals.

We now turn to earthquakes. No country has been absolutely spared by earthquakes. In the districts bounding upon the Baltic, and especially in northern Russia, they have, however, been of a quite harmless type. The reason is that the earth-crust there has been lying undisturbed for long geological epochs and has never been fractured. The comparatively severe earthquake which shook the west coast of Sweden on October 23, 1904, to an unusually heavy degree, without, however, causing any noteworthy damage (a few chimneys were knocked over), was caused by a fault of relatively pronounced character for those districts in the Skager-Rack—a continuation of the deepest fold in the bottom of the North Sea, the so-called Norwegian Trough, which runs parallel to the Norwegian coast. In Germany, the Vogtland and the districts on both sides of the middle Rhine have frequently been visited by earthquakes. Of other European countries, Switzerland, Spain, Italy, and the Balkan Peninsula, as well as the Karst districts of Austria, have often suffered from earthquakes.

According to the committee appointed by the British Association for the investigation of earthquakes—a committee which has contributed a great deal to our knowledge of these great natural phenomena—earthquakes of some importance emanate from certain centres which have been indicated on the subjoined map (Fig. 10). The most important among these regions comprises Farther India, the Sunda Isles, New Guinea, and Northern Australia; it is marked on the map by the letter F. From this district have emanated in the six-year period 1899-1904 no fewer than 249 earthquakes, which have been recorded in many observatories far removed from one another. This earthquake centre F is closely related to the one marked E, in Japan, from which 189 earthquakes have proceeded. Next to this comes the extensive district K with 174 earthquakes, comprising the most important folds in the crust of the Old World, including the mountain chains from the Alps to the Himalaya. This district is interesting, because it has been disturbed by a great many earthquakes, although it is almost entirely situated on the Continent. After that we have the districts A, B, C, with 125, 98, and 95 earthquakes. They are situated near lines of fracture in the earth-crust along the American coast of the Pacific Ocean and the Caribbean Sea. District D, with 78 earthquakes, is similarly situated. The three last-mentioned districts, B, C, D, as well as G, between Madagascar and India, with 85 earthquakes, all seem to be surpassed by the district H in the eastern Atlantic, with its 107 earthquakes. These latter are, however, relatively feeble, and we owe their accurate records probably to the circumstances that a great many earthquake observatories are situated within the immediate surroundings of this district. The same may be said of the district I, or Newfoundland, which is not characterized by many earthquakes, and of the district J, between Iceland and Spitzbergen, with 31 and 19 earthquakes respectively. The last on the list used to be the district L, situated about the South Pole, with only eight earthquakes. This small number is probably merely due to the want of observatories in those parts of the earth. Another district, M, has finally been added, which extends to the southwest from New Zealand. No fewer than 75 intense earthquakes were recorded between March 14 and November 23, 1903, by the Discovery Expedition, in 70° southern latitude and 178° eastern longitude.

Earthquakes commonly occur in swarms or groups. Thus, more than 2000 shocks were counted on Hawaii in March, 1868. During the earthquakes which devastated the district of Phokis, in Greece, in 1870-73, shocks succeeded one another for a long time at intervals of three seconds. During the whole period of three and a half years about half a million shocks were counted, and, further, a quarter of a million subterranean reports which were not accompanied by noticeable concussions. Yet of all these shocks only about 300 did noteworthy damage, and only 35 were considered worth being reported in the newspapers. The concussion of October 23, 1904, belonged to a group which lasted from October 10 to October 28, and in which numerous small tremors were noticed, especially on October 24 and 25. The earthquake of San Francisco commenced on April 18, 1906, at 5 hrs. 12 min. 6 sec. A.M. (Pacific Ocean time), and ended at 5 hrs. 13 min. 11 sec, lasting therefore 1 minute and 5 seconds. Twelve smaller shocks succeeded in the following hour. Before 6 hrs. 52 min. P.M., nineteen further concussions were counted, and various smaller shocks succeeded in the following days.

With such groups of earthquakes weaker tremors usually precede the violent destructive shocks and give a warning. Unfortunately this is not always so, and no warning was given by the earthquakes which destroyed Lisbon in 1755 and Caracas in 1812, nor by those which devastated Agram in 1880, nor, finally, in the case of the San Francisco disaster. A not very severe earthquake without feebler precursors befell Ischia in 1881, while the violent catastrophe which devastated this magnificent island in 1883 was heralded by several warnings. As in San Francisco and Chili in 1906, less violent concussions generally succeed the destructive shocks. Earthquakes like that of Lisbon in 1755, consisting of a single shock, are very rare.

The violent concussions often produce large fissures in the ground. Such were noticed in several places at San Francisco. One of the largest fissures known, that of Midori, in Japan, was caused by the earthquake of October 20, 1891. It left a displacement of the ground ranging up to 6 m. (20 ft.) in the vertical and 4 m. (13 ft.) in the horizontal direction. This crack had a length of not less than 65 km. (40 miles). Extensive fissures were also formed by the earthquakes of Calabria, in 1783, at Monte San Angelo, and in the sandstones of the Bálpakrám Plateau in India, in 1897. In mountainous districts falls of rock are a frequent consequence of the formation of fissures and earthquakes. A large number of rocks fell in the neighborhood of Delphi during the Phokian earthquake. On January 25, 1348, an earthquake sent down a large portion of Mount Dobratsch (in the Alps of Villach, in Carinthia, which is now much frequented by tourists) and buried two towns and seventeen villages. The earthquake of April 18, 1906, in California started from a crack which extends from the mouth of Alder Creek, near Point Arena, running parallel with the coast-line mostly inland, then entering the sea near San Francisco, and turning again inland between Santa Cruz and San José, finally proceeding _via_ Chittenden up to Mount Pinos, a distance of about 600 km. (400 miles), in the direction of N. 35° W. to S. 35° E. Along this crack the two masses of the earth have been displaced so that the ground situated to the southwest of the fissure has been moved by about 3 m. (10 ft.), and in some spots even by 6 m. (20 ft.) towards the northwest. In some localities in Sonoma and Mendocino counties the southwestern part has been raised, but nowhere by more than 1.2 m. (4 ft.). This is the longest crack which has ever been noticed in connection with an earthquake.

The earthquake over, the ground does not always return to its original position, but remains in a more or less wavy condition. This can most easily be observed in districts where streets or railways cross the ground. It is reported, for instance, that the track of the tramway-lines in Market Street, the chief thoroughfare of San Francisco, formed large wavelike curves after the earthquake.

As a consequence of the displacements in the interior of the earth and of the formation of fissures, river courses are changed, springs become exhausted, and new springs arise. That was the case, for instance, in California in 1906. The ground water often rushes out with considerable violence, tearing with it sand and mud and stones, and piling them up, occasionally forming little craters (Fig. 12). Extensive floods may also be caused on such occasions. By such a flood the ancient Olympia was submerged under a layer of river sand which for some time preserved from destruction the ancient Greek masterpieces of art—among them the famous statue of Hermes. The floods afterwards receded, and the treasures of ancient Olympia could be excavated.

Like the natural water channels and arteries in the interior of the earth, water mains are displaced by the concussions. The direct damage caused by the floods is often less important than the damage due to the impossibility of extinguishing the fires which follow the destruction of the buildings. It was the fires that did most of the enormous material damage in the destruction of San Francisco.

Still greater devastation is wrought by the ocean waves thrown up by earthquakes. We have already referred to the flood of Lisbon in 1755, which was felt on the western coast of Norway and Sweden. Another wave, in 1510, devoured 109 mosques and 1070 houses in Constantinople. Another wave, again, invaded Kamaïshi, in Japan, on June 15, 1896, swept away 7600 houses and killed 27,000 people.

We have repeatedly alluded to the disastrous flood-wave of Krakatoa of 1883. This wave traversed the whole of the Indian Ocean, passing to the Cape of Good Hope and Cape Horn, and travelled round half the globe afterwards. Even more remarkable was the aerial wave, which spread like an explosion wave.

While the most violent cannonades are rarely heard for more than 150 km. (95 miles)—in a single case at a distance of 270 km. (170 miles)—the eruption of Krakatoa was heard at Alice Springs, at a distance of 3600 kilometres, and on the island of Rodriguez, at almost 4800 km. (3000 miles). The barographs of the meteorological stations first marked a sudden rise and then a decided sinking of the air pressure, succeeded by a few smaller fluctuations. These air pulses were repeated in some places as many as seven times. We may therefore assume that the aerial wave passed these places three times in the one direction, and three times in the other, travelling round the earth. The velocity of propagation of this wave was 314.2 m. (1030 ft.) per second, corresponding to a temperature of -27° Cent. (17° F.) which prevails at an altitude of about 8 km. (5 miles) above the earth’s surface, at which altitude this wave may have travelled.

Within the last decade a peculiar phenomenon (leading to what is designated variation of latitudes) has been studied. The poles of the axis of the earth appear to move in a very irregular curve about their mean axis. The movement is exceedingly small. The deviation of the North Pole from its mean position does not amount to more than 10 m. (about 33 ft.). It has been believed that these motions of the North Pole are subject to sudden fluctuations after unusually violent earthquakes, especially when such concussions follow at rapid intervals. That would give us, perhaps more than any other observation, an idea of the force of earthquakes, since they would appear to be able to disturb the equilibrium of the whole mass of our globe.

A severely felt effect of earthquakes, though most people perhaps pay little attention to it, is the destruction of submarine cables. The gutta-percha sheaths of cables are frequently found in a fused condition, suggesting volcanic eruptions under the bottom of the sea. We take care now to avoid earthquake centres in laying telegraphic cables. Their positions have been ascertained by the most modern investigations (see Fig. 10).

People have always been inclined to look for a connection between earthquakes and volcanic eruptions. The connection is unquestionable in a large number of violent earthquakes. In order to establish it, the above-mentioned committee of the British Association has compiled the following table of the history of the earthquakes of the Antilles:

1692.—Port Royal, Jamaica, destroyed by an earthquake; land
sinking into the sea. Eruption on St. Kitts.

1718.—Terrible earthquake on St. Vincent, followed by an
eruption.

1766-67.—Great shocks in northeastern South America, in Cuba,
Jamaica, and the Antilles. Eruption on Santa Lucia.

1797.—Earthquake in Quito, loss of 40,000 lives. Concussions
in the Antilles, eruption on Guadeloupe.

1802.—Violent shocks in Antigua. Eruption on Guadeloupe.

1812.—Caracas, capital of Venezuela, totally destroyed by
earthquake. Violent shocks in the Southern States of North
America, commencing on November 11, 1811. Eruptions on St.
Vincent and Guadeloupe.

1835-36.—Violent concussions in Chili and Central America.
Eruption on Guadeloupe.