The first attempt, however, to frame a satisfactory theory of volcanic action, and to show the part which volcanoes have played in the past history of our globe, together with their place in its present economy, was made in 1825, by Poulett Scrope, whose great work, 'Considerations on Volcanoes,' may be regarded as the earliest systematic treatise on Vulcanology. Since the publication of this work, many new lines of inquiry have been opened up in connection with the subject, and fresh methods of research have been devised and applied to it. More exact observations of travellers over wider areas have greatly multiplied the facts upon which we may reason and speculate, and many erroneous hypotheses which had grown up in connection with the subject have been removed by patient and critical inquiry. We propose in the following pages to give an outline of the present state of knowledge upon the subject, and to indicate the bearings of those conclusions which have already been arrived at, upon the great questions of the history of our globe and the relations which it bears to the other portions of the universe. In attempting this task we cannot do better than take up the several lines of inquiry in the order in which they have been seized upon and worked out by the original investigators; for never, perhaps, is the development of thought in the individual mind so natural in its methods, and so permanent in its effects, as when it obeys those laws which determined its growth in the collective mind of the race. In our minds, as in our bodies, development in the individual is an epitome, or microcosmic reproduction, of evolution in the species. CHAPTER II. THE NATURE OF VOLCANIC ACTION. The dose investigation of what goes on within a volcanic vent may appear at first sight to be a task beset with so many difficulties and dangers that we may be tempted to abandon it as altogether hopeless. At the first recorded eruption of Vesuvius the elder Pliny lost his life in an attempt to approach the mountain and examine the action which was taking place there; and during the last great outburst of the same volcano a band of Neapolitan students, whose curiosity was greater than their prudence, shared the same fate.