N. S. Shaler

“ The thicker the atmosphere the more slowly the matter would fall; the mist would be frozen, as is the water in all the higher-lying clouds, even on a summer day, and, entangling the volcanic dust in its meshes, would fall into the region of the air currents, and so journey over all the lands and seas. ”

“ Now imagine a gun standing vertically, with its mouth a mile or more in diameter, and discharging its gases into the atmosphere with several times the speed with which they escape from a piece of artillery, and we will have the essential conditions of a volcanic explosion; only in place of the momentary outrush of the cannon we must imagine the explosion to endure for hours, or perhaps for days. ”

“ Having now examined that part of the sunset phenomena that is evident to the eye, let us inquire how the dust and vapor was driven to such a height into the atmosphere, and so rapidly distributed over the earth. If we consider what takes place in any violent eruption of a volcano, we will see the explanation of these facts. In the case of this Krakatoa eruption, as in that of Skapta Jokul, indeed in all great eruptions, we easily see that the principal thing that occurs is a furious uprush of steam from the crater, bearing with it a vast quantity of pulverized rock, called dust or ashes. ”

“ Watching this faint cloud, we see that it is constantly changing its shape; dim streamers extend from it from time to time, and then fade away. Sometimes it is much stronger on one side of the sun than on the other. ”

“ It appears possible that volcanoes may operate to change the climate of the earth in at least two ways. In the first place, the great amount of water in the form of steam that they hurl into the air tends to increase the rainfall over a wide region; the greater part of this water will fall near the volcano, but the effect will doubtless be of importance over a wide area. If this rain falls from skies that have any considerable amount of their sunlight fended off by the dust wrap that may be formed over them, this water will be apt to fall in the form of snow. ”

“ To project stones beyond the earth’s power to recall them requires a velocity that need not exceed seven miles a second. We have no proof of such extreme speed of uprising in any volcanic eruptions, but there are many reasons for believing that it is not altogether beyond the power of the greater eruptions to accomplish this work.
There is yet another lesson that the Krakatoa convulsion has for us: that is, a lesson in favor of a little more humility on the part of those semi-scientific men who fancy that they know the mechanism of the world as a watchmaker knows the wheels of a watch. ”

“ If the reader has examined these luminous skies with care, he will have observed that at midday, with an otherwise clear sky, the sun seems to be in a vast tract of thin whitish-brown vapor, looking like a thin mist, which is most evident a few degrees from the sun, and fades away insensibly, until at twenty degrees or less from the sun it imperceptibly melts into the apparently clear sky. ”

“ As their phenomena of color show that they are not water vapor alone, it is a fair conclusion that they are made up of a mixture of dust and water vapor, such as occurs in our chimney smoke. Our ordinary coal smoke is always composed in large part of steam, in which the little bits of carbon are mingled, as the soot is in the London fog. When dust of any kind becomes entangled in water vapor, the union is of a singularly permanent nature, the two being unwilling to separate until they fall as rain. ”

“ If we reduce the rate of the movement to that of a shot when it leaves a gun, we will still have about one third of this quantity. If all the gas discharged from a volcano stayed in the form of highly heated gas, then the pressure of the earth’s atmosphere would be doubled in about a fortnight, and even a day of eruption should add something like a pound to the pressure of the atmosphere on a square foot of surface. ”

“ The mist about the noonday sun is a little more brown than it would be if it were watery vapor alone, and the sunset glow of the cloud appears to be from a less lustrous surface than clouds of pure watery mist would afford. ”

“ At several points in Europe the new-fallen snow contains particles of volcanic dust essentially like those that fell upon the decks of ships near the point of eruption, and which presumably are the heavier bits that have descended from the dust-cloud in the upper air.
Still further, it has been shown that these curious appearances of the sky occurred more quickly in the district near the volcano than in regions remote from it. It is not easy to determine the precise times when the sunset and sunrise became so brilliant ”

“ The way in which men take the unexpected is an excellent gauge of their state of mind. Sudden changes in the face of nature bring the man out of his burrow and exhibit his hidden motives. Fifty years ago the meteoric shower of 1833 showed that the less cultivated class, even in America, still looked upon the accidents of the skies as signs of heavenly wrath and portents of coming ills. ”

“ If it were the purpose of this article to explain the phenomena of volcanoes, it would be shown that the volcanic steam is the water that in old ages was inclosed in the small interstices of the rocks as they were formed on the ancient sea floors, and which became heated from the thick coating, or blanket, of other rocks deposited above. When by some chance fracture these gases of the buried water escape, they force quantities of the heated rock before them, as they rush into the air. ”

“ This matter, being intensely illuminated, is made visible in the region near the sun; elsewhere it is not dense enough to alter the blue of the sky. If we follow the descending sun, we find that when it begins to get into the mists of the horizon it no longer shows this ash-colored fringe, which melts into the dim, vaporous color that seems to encircle the horizon, but which is in fact due to the greater thickness and humidity of the air through which we then look. ”

“ It is this resistance that keeps the upper clouds floating so long and so high above the earth. The particles of water are constantly falling through the air, but owing to their fineness they may fall only a few inches each day. The same principle is shown in the settling of mud in water. A tumbler of Mississippi water will require days to deposit its mud. We have only to suppose that the particles of mingled dust and water that constitute these volcanic clouds are extremely small, to account for months, or even years, of suspension in the air. ”

“ The long time that elapses after the sun goes below the horizon before these upper vapors find themselves at the right angle to reflect the light to us, and the long duration of this glow, show us that the volcanic vapor is much further above the earth than any common clouds. Computations based on the duration of this sunset light on the mists in question indicate that they must be somewhere near fifty thousand feet above the surface, or between nine and ten miles high. ”

“ In 1783, Skapta Jokul, one of the greatest of our volcanoes, passed through a period of eruption which, for its energy, was the most violent ever known in any but a Javanese volcano. Shortly after this eruption occurred, the English skies put on the fiery aspect that our own have at present. In those days men still looked to the heavens for portents, and deep alarm took possession of the people. ”

“ The most likely conjecture as to the origin of these meteors that can be made is that in certain periods of particularly intense eruptions the ejection of volcanoes — those it may be of other planets, as well as of the earth — attain such an extreme velocity that they fly clear beyond the control of the orb from which they are projected, and are left to swing through space in orbits determined by the control of the sun. At times these bodies would perhaps come sufficiently into the sphere of the gravitation of a planet to be precipitated upon its surface ”

“ If the dust wrap remained for any considerable time in the air, — and as far as we can see it might remain for several years, for this dust that our air now bears has been afloat for nearly half a year, with no sign of diminution, — then the chapter of accidents might lay the foundations of a glacial period which might endure long after the cause that led to its beginning had ceased to exist. ”

“ Upon this heat all the machinery of the earth’s physical and organic life most intimately depends. Take but the hundredth part of it away, and all the life of the earth would feel the loss of power. The air currents would become feebler, the ocean streams less strong; thousands of animals and plants would find their conditions changed, so that the boundaries of the provinces they occupy would be altered, or even life itself abandoned after a few years of struggle. ”

“ The strongest piece of modern artillery will, however, drive a ball straight upwards to the height of about four miles. it may easily be seen, even in small volcanoes such as Vesuvius, that more than this distance is attained by the substances which the eruption throws out. In great volcanoes, such as Krakatoa and many of those of Java and elsewhere, it may be that eruptions eject their matter to several times this height. Masses of considerable size, thrown out of volcanoes, have been known to fall four or five miles away from the crater. ”

“ As the lightest ordinary clouds probably do not rise more than about thirty thousand feet above the earth, in northern regions, in the winter season, it is evident that the great height of these volcanic clouds is a part of the problem with which we have to deal. ”

“ The first scientific observers of the red sunsets generally inclined to the opinion that they were produced by the falling upon the earth of some clouds of finely divided matter, such as are thought to give rise to the zodiacal light, — cosmic vapor, as it has been unhappily called. ”

“ Now the smaller any bits of matter are, the larger in proportion is their surface to their weight. A certain descending force is required to push the resisting atoms of air apart, and so permit the descent of the gravitating particle. ”

“ Allowing all that we can for wind carriage, it seems necessary to believe that these fragments must have had at least five or six times the speed of motion that we can impress on a cannon-ball, arid must have gone upward with nearly enough velocity to carry them beyond the sphere of the earth’s attraction. ”

“ The invention was never profitable, except to the geologist, who finds in it a capital illustration of the action that takes place in highly heated rocks when, by the rents at the volcano’s base, they are suddenly permitted to escape to the air. ”