PREFACE.
Some explanation seems desirable of how it is that the following Report to the Royal Society of London appears in form of the present volumes, and why not at an earlier period.
The earthquake of December, 1857, by almost the first notices that reached England, revealed itself as the third greatest in extent and severity of which there is any record as having occurred in Europe.
Impressed with its observational value to science, the Author at once addressed the following letter to the then President of the Royal Society:—
"My Lord,
"The very recent occurrence of a great earthquake in the Neopolitan territory presents an opportunity of the highest interest and value for the advancement of this branch of Terrestrial Physics.
"Within the last ten years only Seismology has taken its place in cosmic science—and up to this time no earthquake has had its secondary or resultant phenomena—sought
