The question suggested above as to the possibility of volcanic ejections throwing matter from the earth beyond the control of its gravitative energy is one of great scientific interest. Computations (not altogether trustworthy) show that a body leaving the earth's surface under the conditions of a cannon ball fired vertically upward would have to possess a velocity at the start of at least seven miles a second in order to go free into space. It would at first sight seem that we should be able to reckon whether volcanoes can propel earth matter upward with this speed. In fact, however, sufficient data are not obtainable; we only know in a general way that the column of vapour rises to the height of thirty or forty thousand feet, and this in eruptions of no great magnitude. In an accident such as that at Krakatoa, even if an observer were near enough to see clearly what was going on, the chance of his surviving the disturbance would be small. Moreover, the ascending vapours, owing to their expansion of the steam in the column, begin to fly out sideways on its periphery, so that the upper part of the central section in the discharge is not visible from the earth.
It is in the central section of the uprushing mass, if anywhere, that the dust might attain the height necessary to put it beyond the earth's attraction, bringing it fairly into the realm of the solar system, or to the position where its own motion and the attraction of the other spheres would give it an independent orbital movement about the sun, or perhaps about the earth. We can only say that observations on the height of volcanic ejections are extremely desirable; they can probably only be made from a balloon. An ascension thus made beyond the cloud disk which the eruption produces might bring the observer where he could discern enough to determine the matter. Although the movements of the rocky particles could not be observed, the colour which they would give to the heavens might tell the story which we wish to know. There is evidence that large masses of stone hurled up by volcanic eruption have fallen seven miles from the base of the cone. Assuming that the masses went straight upward at the beginning of their ascent, and that they were afterward borne outwardly by the expansion of the column, computations which have a general but no absolute value appear to indicate that the masses attained a height of from thirty to fifty miles, and had an initial velocity which, if doubled, might have carried them into space.