AT THE SUMMIT OF POPOCATEPETL.
Virgil’s Æneid affords a passage containing the Roman myth concerning Mt. Ætna, and showing that the people of Virgil’s day were acquainted with the phenomena of that mountain. Thus Dryden has translated:
“The flagging wind forsook us with the sun,
And wearied, on Cyclopean shores we run.
The port, capacious and secure from wind,
Is to the fort of thundering Ætna joined,
By turns a pitchy cloud she rolls on high,
And flakes of mountain flames that arch the sky;
Oft from her bowels massy rocks are thrown,
And shivered by the force, come piece-meal down;
Oft liquid cakes of burning sulphur flow,
Fed from the fiery springs that burn below.
Enceladus, they say, transfixed by Jove,
With blasted limbs came trembling from above,
And where he fell, th’ avenging father drew
This flaming hell, and on his body threw.
As often as he turns his weary sides,
He shakes the solid hill, and smoke the heaven hides.”
This conception was borrowed from the Greeks, one of whose poets has told us
“How shaggy-breasted Typhon lay,
From sea-girt Cuma to Trinacria’s bay.”
Yet, even among the ancients an occasional great mind disregarded popular superstition, and enunciated just and rational views upon the matter. The elder Pliny lost his life in an effort to observe closely an eruption of Vesuvius. But the ideas advanced by these men were speedily forgotten; and the exact scientific examination of volcanoes is of the past hundred years, the great Italian, Spallanzani, being the first to publish a series of valuable observations on the volcanoes of his own land.
The ancients were acquainted only with the few active volcanoes distributed about the Mediterranean Sea, and the casual thinker might hence suppose their opportunities for observation were quite limited. But volcanic principles are the same everywhere, differing only in violence. In the Lipari Islands is situated the volcanic cone of Stromboli, which has been in a state of constant activity, though very mild, for at least two thousand years. This affords excellent opportunities for study, and much of our most valuable information on the topic is derived from careful observation of it. When the wind is steady in any quarter, a person may sit to windward for hours within a few yards of the boiling mass, while the noxious vapors and gases are borne away in the other direction.
The expulsive agent is in all cases steam, mingled to a greater or less degree with other vapors or gases. Its operation may be simply illustrated. Pure water does not readily boil over in any open vessel of ordinary dimensions. But if the vessel be very deep in proportion to its width, and the heat is applied at the base only, it boils over more readily. Now, if instead of water, we substitute porridge, thick molasses, or any similar thick or viscid material, the bubbles of steam rise slowly; and if rapidly generated, they force the matter out at the top ere they escape. Such bubbles as reach the top, burst, throwing tiny particles of the mass into the air.