Cosmos: A Sketch of the Physical Description of the Universe Part 21

[footnote] *On the frequency of earthquakes in Cashmir, see Troyer's German translation of the ancient 'Radjataringini', vol. ii., p. 297, and Carl Hugel, 'Reisen', bd. ii., s. 184.

As the impeded activity of the volcano acts upon the shocks of the earth's surface, so do the latter react on the volcanic phenomena. Openings of fissures favor the rising of cones of eruption, and the processes which take place in these cones, by forming a free communication with the atmosphere.

A column of smoke, which had been observed to rise for months together from the volcano of Pasto, in South America, suddenly disappeared, when on the 4th of February, 1797, the province of Quito, situated at a distance of 192 miles to the south, suffered from the great earthquake of Riobamba. After the earth had continued to tremble for some time through out the whole of Syria, in the Cyclades, and in Euboea, the shocks suddenly ceased on the eruption of a stream of hot mud p 215 on the Lelantine plains near Chalcia.*

[footnote] * Strabo, lib. i., p. 100, Casaub. That the expression [Greek words] does not mean erupted mud, but lava, is obvious from a pa.s.sage in Strabo, lib. vi., p. 412. Compare Walter, in his 'Abnahme der Vulkanischen Thatigkeit in Historischen Zeiten' (On the Decrease of Volcanic Activity during Historical Times), 1844, s. 25.

The intelligent geographer of Amasea, to whom we are indebted for the notice of this circ.u.mstance, further remarks: "Since the craters of Aetna have been opened, which yield a pa.s.sage to the escape of fire, and since burning ma.s.ses and water have been ejected, the country near the sea-sh.o.r.e has not been so much shaken as at the time previous to the separation of Sicily from Lower Italy, when all communications with the external surface were closed."

We thus recognize in earthquakes the existence of a volcanic force, which, although every where manifested, and as generally diffused as the internal heat of our planet, attains but rarely, and then only at separate points, sufficient intensity to exhibit the phenomenon of eruptions. The formation of veins, that is to say, the filling up of fissures with crystalline ma.s.ses bursting forth from the interior (as basalt, melaphyre, and greenstone), gradually disturbs the free intercommunication of elastic vapors. This tension acts in three different ways, either in causing disruptions, or sudden and retroversed elevations, or, finally, as was first observed in a great part of Sweden, in producing changes in the relative level of the sea and land, which, although continuous, are only appreciable at intervals of long period.

Before we leave the important phenomena which we have considered not so much in their individual characteristics as in their general physical and geognostical relations, I would advert to the deep and peculiar impression left on the mind by the first earthquake which we experience, eeven where it is not attended by any subterranean noise.*

[footnote] *[Dr. Tschudi, in his interesting work, 'Travels in Peru', translated from the German by Thomasina Ross, p. 170, 1847, describes strikingly the effect of an earthquake upon the native and upon the stranger. "No familiarity with the phenomenon can blunt this feeling. The inhabitant of Lima, who from childhood has frequently witnessed these convulsions of nature, is roused from his sleep by the shock, and rushes from his apartment with the cry of 'Misericordia!' The foreigner from the north of Europe, who knows nothing of earthquakes but by description, waits with impatience to feel the movement of the earth, and longs to hear with his own ear the subterranean sounds which he has. .h.i.therto considered fabulous. With levity he treats the apprehension of a coming convulsion, and laughs at the fears of the natives: but, as soon as his wish is gratified, he is terror-stricken, and is involuntarily prompted to seek safety in flight."] -- Tr.

This impression is not, p 216 in my opinion, the result of a recollection of those fearful pictures of devastation presented to our imaginations by the historical narratives of the past, but is rather due to the sudden revelation of the delusive nature of the inherent faith by which we had clung to a belief in the immobility of the solid parts of the earth. We are accustomed from early childhood to draw a contrast between the mobility of water and the immobility of the soil on which we tread; and this feeling is confirmed by the evidence of our senses. When, therefore, we suddenly feel the ground move beneath us, a mysterious and natural force, with which we are previously unacquainted, is revealed to us as an active disturbance of stability. A moment destroys the illusion of a whole life; our deceptive faith in the repose of nature vanishes, and we feel transported, as it were, into a realm of unknown destructive forces. Every sound -- the faintest motion in the air -- arrests our attention, and we no longer trust the ground on which we stand.

Animals, especially dogs and swine, partic.i.p.ate in the same anxious disquietude; and even the crocodiles of the Orinoco, which are at other times as dumb as our little lizards, leave the trembling bed of the river, and run with loud cries into the adjacent forests.

To man the earthquake conveys an idea of some universal and unlimited danger. We may flee from the crater of a volcano in active eruption, or from the dwelling whose destruction is threatened by the approach of the lava stream; but in an earthquake, direct our flight whithersoever we will, we still feel as if we trod upon the very focus of destruction. This condition of the mind is not of long duration, although it takes its origin in the deepest recesses of our nature; and when a series of faint shocks succeed one another, the inhabitants of the country soon lose every trace of fear. On the coasts of Peru, where rain and hail are unknown, no less than the rolling thunder and the flas.h.i.+ng lightning, these luminous explosions of the atmosphere are replaced by the subterranean noises which accompany earthquakes.*

[footnote] *["Along the whole coast of Peru the atmosphere is almost uniformly in a state of repose. It is not illuminated by the lightning's flash, or disturbed by the roar of the thunder; no deluges of rain, no fierce hurricanes, destroy the fruits of the fields, and with them the hopes of the husbandman. But the mildness of the elements above ground is frightfully counterbalanced by their subterranean fury. Lima is frequently visited by earthquakes, and several times the city has been reduced to a ma.s.s of ruins. At an average, forty-five shocks may be counted on in the year. Most of them occur in the later part of October, in November, December, January, May, and June. Experience gives reason to expect the visitation of two desolating earthquakes in a century. The period between the two is from forty to sixty years. The most considerable catastrophes experienced in Lima since Europeans have visited the west coast of South America happened in the years 1586, 1630, 1687, 1713, 1746, 1806. There is reason to fear that in the course of a few years this city may be the prey of another such visitation."] --Tr.

Long habit, and the very p 217 prevalent opinion that dangerous shocks are only to be apprehended two or three times in the course of a century, cause faint oscillations of the soil to be regarded in Lima with scarcely more attention than a hail storm in the temperate zone.

Having thus taken a general view of the activity -- the inner life, as it were -- of the Earth, in respect to its internal heat, its electro-magnetic tension, its emanation of light at the poles, and its irregularly-recurring phenomena of motion, we will now proceed to the consideration of the material products, the chemical changes in the earth's surface, and the composition of the atmosphere, which are all dependent on planetary vital activity. We see issue from the ground steam and gaseous carbonic acid, almost always free from the admixture of nitrogen;* carbureted hydrogen gas, which has been used in the Chinese province Sse-tschuan** for several thousand years, and recently in the village of Fredonia, in the State of New York, United States, in cooking and for illumination; sulphureted hydrogen gas and sulphurous vapors; and, more rarely,*** sulphurous and hydrochloric acids.****

[footnote] * Bischof's comprehensive work, 'Warmelchere des inneren Erdkorpers'.

[footnote] **On the Artesian fire-springs (Ho-tsing) in China, and the ancient use of portable gas (in bamboo canes) in the city of Khiung-tsheu, see Klaproth, in my 'Asie Centrale', t. iii., p. 519-530.

[footnote] *** Boussingault ('Annales de Chimie', t. lii., p. 181) observed no evolution of hydrochloric acid from the volcanoes of New Granada, while Monticelli found it in enormous quant.i.ty in the eruption of Vesuvius in 1813.

[footnote] ****[Of the gaseous compounds of sulphur, one, sulphurous acid, appears to predominate chiefly in volcanoes possessing a certain degree of activity, while the other, sulphureted hydrogen, has been most frequently perceived among those in a dormant condition. The occurrence of abundant exhalations of sulphuric acid, which have been hitherto noticed chiefly in extinct volcanoes, as for instance, in a stream issuing from that of Purace, between Bogota and Quito, from extinct volcanoes in Java, is satisfactorily explained in a recent paper by M. Dumas, 'Annales de Chimie', Dec., 1846.

He shows that when sulphureted hydrogen, at a temperature above 100 degrees Fahr., and still better when near 190 degrees, comes in contact with certain porous bodies, a catalytic action is set up, by which water, sulphuric acid, and sulphur are produced. Hence probably the vast deposits of sulphur, a.s.sociated with sulphates of lime and strontian, which are met with in the western parts of Sicily.] -- Tr.

Such effusions p 218 from the fissures of the earth not only occur in the districts of still burning or long-extinguished volcanoes, but they may likewise be observed occasionally in districts where neither trachyte nor any other volcanic rocks are exposed on the earth's surface. In the chain of Quindiu I have seen sulphur deposited in mica slate from warm sulphurous vapor at an elevation of 6832 feet* above the level of the sea, while the same species of rock, which was formerly regarded as primitive, contains, in the Cerro Cuello, near Tiscan, south of Quito, an immense deposit of sulphur imbedded in pure quartz.

[footnote] * Humboldt, 'Recucil d'Observ. Astronomiques', t. i., p. 311 ('Nivellement Barometrique de la Cordillere des Andes', No. 206).

Exhalations of carbonic acid ('mofettes') are even in our days to be considered as the most important of all gaseous emanations, with respect to their number and the amount of their effusion. We see in Germany, in the deep valleys of the Eifel, in the neighborhood of the Lake of Laach,* in the crater-like valley of the Wehr and in Western Bohemia, exhalations of carbonic acid gas manifest themselves as the last efforts of volcanic activity in or near the foci of an earlier world.

[footnote] *[The Lake of Laach, in the district of the Eifel, is an expanse of water two miles in circ.u.mference. The thickness of the vegetation on the sides of its crater-like basin renders it difficult to discover the nature of the subjacent rock, but it is probably composed of black cellular augitic lava. The sides of the crater present numerous loose ma.s.ses, which appear to have been ejected, and consist of gla.s.sy feldspar, ice-spar, sodalite, hauyne, spinellane, and leucite. The resemblance between these products and the ma.s.ses formerly ejected from Vesuvius is most remarkable. (Daubeney 'On Volcanoes', p. 81.) Dr. Hibbert regards the Lake of Laach as formed in the first instance by a crack caused by the cooling of the crust of the earth, which was widened afterward into a circular cavity by the expansive force of elastic vapors. See 'History of the Extinct Volcanoes of the Basin of Neuwied', 1832.] -- Tr.

In those earlier periods, when a higher terrestrial temperature existed, and when a great number of fissures still remained unfilled, the processes we have described acted more powerfully, and carbonic acid and hot steam were mixed in larger quant.i.ties in the atmosphere, from whence it follows, as Adolph Bronguiart has ingeniously shown,* that the primitive vegetable world must have exhibited almost every where, and independently of geographical position, the most luxurious abundance and the fullest development of organism.

[footnote] *Adolph Bronguiart, in the 'Annales des Sciences Naturelles', t.

xv., p. 225.

In these constantly warm and damp atmospheric strata, saturated with p 219 carbonic acid, vegetation must have attained a degree of vital activity, and derived the superabundance of nutrition necessary to furnish materials for the formation of the beds of lignite (coal) const.i.tuting the inexhaustible means on which are based the physical power and prosperity of nations. Such ma.s.ses are distributed in basins over certain parts of Europe, occurring in large quant.i.ties in the British Islands, in Belgium, in France, in the provinces of the Lower Rhine, and in Upper Silesia. At the same primitive period of universal volcanic activity, those enormous quant.i.ties of carbon must also have escaped from the earth which are contained in limestone rocks, and which, if seprated from oxygen and reduced to a solid form, would const.i.tute about the eighth part of the absolute bulk of these mountain ma.s.ses.*

[footnote] * Bischof, op. cit., s. 324, Anm. 2.

That portion of the carbon which was not taken up by alkaline earths, but remained mixed with the atmosphere, as carbonic acid, was gradually consumed by the vegetation of the earlier stages of processes of vegetable life, only retained the small quant.i.ty which it now possesses, and which is not injurious to the sulphurous vapor have occasioned the destruction of the species of mollusca and fish which inhabited the inland waters of the earlier world, and have given rise to the formation of the contorted beds of gypsum, which have doubtless been frequently affected by shocks of earthquakes.

Gaseous and liquid fluids, mud, and molten earths, ejected from the craters of volcanoes, which are themselves only a kind of "intermittent springs,"

rise from the earth under precisely a.n.a.logous physical relations.*

[footnote] *Humboldt, 'Asie Centrale', t. i., p. 43.

All these substances owe their temperature and their chemical character to the place of their origin. The 'mean' temperature of aqueous springs is less than that of the air at the point whence they emerge, if the water flow from a height; but their heat increases with the depth of the strata with which they are in contact at their origin. We have already spoken of the numerical law regulating this increase. The blending of waters that have come from the height of a mountain with those that have sprung from the depths of the earth, render it difficult to determine the position of the 'isogeothermal lines'* (lines of equal internal p 220 terrestrial temperature, when this determination is to be made from the temperature of flowing springs.

[footnote] *On the theory of isogeothermal (chthonisothermal) lines, consult the ingenious labors of Kupffer, in Pogg, 'Annalen', bd xv., s. 184, and bd x.x.xii., s. 270, in the 'Voyage dans l'Oural', p. 382-298, and in the 'Edinburgh Journal of Science', New Series, vol. iv., p. 355. See, also, Kamtz, 'Lehrb. der Meteor.', bd. ii., s. 217; and, on the ascent of the chthonisothermal lines in mountainous districts, Bischof, s. 174-198.

Such at any rate, is the result I have arrived at from my own observations and those of my fellow-travelers in Northern Asia. The temperature of springs, which has become the subject of such continuous physical investigation during the last half century, depends, like the elevation of the line of perpetual snow, on very many simultaneous and deeply-involved causes. It is a function of the temperature of the stratum in which they take their rise, of the specific heat of the soil, and of the quant.i.ty and temperature of the meteoric water,* which is itself different from the temperature of the lower strata of the atmosphere, according to the different modes of its origin in rain, snow, or hail.**

[footnote] *Leop. v. Buch, in Pogg., 'Annalen', bd. xii., s. 405.

[footnote] ** On the temperature of the drops, of rain in c.u.mana, which fell to 72 degrees, when the temperature of the air shortly before had been 86 degrees and 88 degrees, and during the rain sank to 74 degrees, see my 'Relat. Hist.', t. ii., p. 22. The rain-drops, while falling, change the normal temperature they originally possessed, which depends on the height of the clouds from which they fell, and their heating on their upper surface by the solar rays. The rain-drops, on their first production, have a higher temperature than the surrounding medium in the superior strata of our atmosphere, in consequence of the liberation of their latent heat; and they continue to rise in temperature, since, in falling through lower and warmer strata, vapor is precipitated on them, and they thus increase in size (Bischof, 'Warmelehre des inneren Erdkorpers' s. 73); but this additional heating is compensated for by evaporation. The cooling of the air by rain (putting out of the question what probably belongs to the electric process in storms) is effected by the drops, which are themselves of lower temperature, in consequence of the cold situation in which they were formed, and bring down with them a portion of the higher colder air, and which finally, by moistening the ground, give rise to evaporation. The cooling of the air by rain (putting out of the question what probably belongs to the electric process in storms) is effected by the drops, which are themselves of lower temperature, in consequence of the cold situation in which they were formed, and bringi down with them a portion of the higher colder air, and which finally, by moistening the ground, give rise to evaporation.

These are the ordinary relations of the phenomenon. When, as occasionally happens, the rain-drops are warmer than the lower strata of the atmosphere (Humboldt, 'Rel. Hist.', t. iii., p. 513), the cause must probably be sought in higher warmer currents, or in a higher temperature of widely-extended and not very thick clouds, from the action of the sun's rays. How, moreover, the phenomenon of supplementary rainbows, which are explained by the interference of light, is connected with the original and increasing size of the falling drops, and how an optical phenomenon, if we know how to observe it accurately, may enlighten us regarding a meteorological process, according to diversity of zone, has been shown, with much talent and ingenuity, by Arago, in the 'Annuaire' for 1836, p. 300.

Cold springs can only indicate the mean atmospheric temperature p 221 when they are unmixed with the waters rising from great depths, or descending from considerable mountain elevations, and when they have pa.s.sed through a long course at a depth from the surface of the earth which is equal in our lat.i.tudes to 40 or 60 feet, and according to Boussingault, to about one foot in the equinoctial regions,* these being the depths at which the invariability of the temperature begins in the temperate and torrid zones, that is to say, the depths at which horary, diurnal, and monthly changes of heat in the atmosphere cease to be perceived.