VOLCANOES.
CHAPTER I.
INTRODUCTORY: NATURE OF THE INQUIRY.
'What is a volcano?' This is a familiar question, often addressed to us in our youth, which 'Catechisms of Universal Knowledge,' and similar school manuals, have taught us to reply to in some such terms as the following: 'A volcano is a burning mountain, from the summit of which issue smoke and flames.' Such a statement as this, it is probable, does not unfairly represent the ideas which are, even at the present day, popularly entertained upon the subject.
But in this, as in so many other cases, our first step towards the acquirement of scientific or exact knowledge, must be the unlearning of what we have before been led to regard as true. The description which we have quoted is not merely incomplete and inadequate as a whole, but each individual proposition of which it is made up is grossly inaccurate, and, what is worse, perversely misleading. In the first place, the action which takes place at volcanoes is not 'burning,' or combustion, and bears, indeed, no relation whatever to that well-known process. Nor are volcanoes necessarily 'mountains' at all; essentially, they are just the reverse—namely, holes in the earth's crust, or outer portion, by means of which a communication is kept up between the surface and the interior of our globe. When mountains do exist at centres of volcanic activity, they are simply the heaps of materials thrown out of these holes, and must therefore be regarded not as the causes but as the consequences of the volcanic action. Neither does this action always take place at the 'summits' of volcanic mountains, when such exist, for eruptions occur quite as frequently on their sides or at their base. That, too, which popular fancy regards as 'smoke' is really condensing steam or watery vapour, and the supposed raging 'flames' are nothing more than the glowing light of a mass of molten material reflected from these vapour clouds.
It is not difficult to understand how these false notions on the subject of volcanic action have come to be so generally prevalent. In the earlier stages of its development, the human mind is much more congenially employed in drinking in that which is marvellous than in searching for that which is true. It must be admitted, too, that the grand and striking phenomena displayed by volcanoes are especially calculated to inspire terror and to excite superstition, and such feelings most operate in preventing those close and accurate observations which alone can form the basis of scientific reasoning.
IDEAS OF THE ANCIENTS.
The ancients were acquainted only with the four or five active volcanoes in the Mediterranean area; the term 'volcano' being the name of one of these (Vulcano, or Volcano, in the Lipari Islands), which has come to be applied to all similar phenomena. It is only in comparatively modern times that it has become a known £act that many hundreds of volcanoes exist upon the globe, and are scattered over almost every part of its surface. Classical mythology appropriated Vulcano as the forge of Hephæstus, and his Roman representative Vulcan, while Etna was regarded as formed by the mountains under which a vengeful deity had buried the rebellious Typhon; it may be imagined, therefore, that any endeavour to more closely investigate the phenomena displayed at these localities would be regarded, not simply as an act of temerity, but as one of actual impiety. In mediæval times similar feelings would operate with not less force in the same direction, for the popular belief identified the subterranean fires with a place of everlasting torment; Vulcano was regarded as the place of punishment of the Arian Emperor Theodosius, while Etna was assigned to poor Anne Boleyn, the perverter of faith in the person of its stoutest defender. That such feelings of superstitious terror in connection with volcanoes are, even at the present day, far from being extinct, will be attested by every traveller who, in carrying on investigations about volcanic centres, has had to avail himself of the assistance of guides and attendants from among the common people.
Among the great writers of antiquity we find several who had so far emancipated their minds from the popular superstitions as to be able to enunciate just and rational views upon the subject of volcanoes. Until quite recent times, however, their teaching was quite forgotten or neglected, and the modern science of Vulcanology may be said to have entirely grown up within the last one hundred years.
The great pioneer in this important branch of research was the illustrious Italian naturalist Spallanzani, who, in the year 1788, visited the several volcanoes of his native land, and published an account of the numerous valuable and original observations which he had made upon them. About the same time the French geologist Dolomieu showed how much light might be thrown on the nature of volcanic action by a study of the various materials which are ejected from volcanic vents; while our own countryman. Sir William Hamilton, was engaged in a systematic study of the changes in form of volcanic mountains, and of the causes which determine their growth. At a somewhat later date the three German naturalists. Von Buch, Humboldt, and Abich, greatly extended our knowledge of volcanoes by their travels in different portions of the globe.
CHARACTER OF MODERN RESEARCHES.