The Earthquake of October, 1863. 299 



hundred miles thick, and Professor Wm. Thompson, making 

 independent calculations from another class of well-ascertained 

 facts, concludes that it must be as thick as half its radius, and 

 thus the notion of its being a bottle full of fiery fluid is defini- 

 tively dispelled. 



What, then, is an earthquake ? It would seem to be a con- 

 cussion given to a portion of the earth at a certain depth below 

 the surface by forces of an igneous kind. A sudden heating 

 and expansion, a sudden irruption into a place where there was 

 no room for it, of a fluid or gaseous matter, would, so to speak, 

 give a thump in all directions to surrounding substances. The 

 particles struck would hand on the blow, just as one billiard-ball 

 transmits it to another, and some of the waves of this concussion 

 would make their way towards the surface, and emerge at a cer- 

 tain angle, capable of being observed. 



Until a very recent period no one thought of applying the 

 principles of mechanics to the elucidation of the phenomena of 

 earthquakes, and to Mr. Mallet belongs the chief credit of the 

 great advance that has been made in the methods of observing 

 and interpreting the effects they produce. His great work on 

 Observational Seismology* is the authority to which all students 

 must refer, and as it is comparatively little known outside a 

 limited circle of scientific men, we propose to resume the sub- 

 jects of earthquakes in our next number, and to do our best to 

 present a difficult and very technical subject in a popular form. 

 To many minds the name Seismology will be as alarming as an 

 earthquake itself. The meaning of the word will, however, be 

 at once apparent to the Greek scholar, as - it is derived from 

 seismos, a concussion, and logos, a discourse; and if we followed 

 the good fashion of the Germans in inventing vernacular names, 

 we might convert all the "ologies" into " talk-abouts/' or 

 " lores/'' and Seismology would be "shock talk-about," or 

 " shock-lore " — a dissertation on concussions and their 

 effects. 



Mr. Mallet's work ought to be found in the library of every 

 scientific institution, and in all other public libraries that make 

 any pretence to further intellectual pursuits. It belongs to a 

 class of richly illustrated books of high practical value, which 

 are necessarily too expensive for most private students to pur- 

 chase in any quantity, but which must be made accessible, if 

 the higher branches of education are to progress. 



* The First Principles of Observational Seismology, as Developed in the Report 

 to the Royal Society of London, of the Expedition made by command of the Society 

 into the interior of the Kingdom of Naples, to investigate the circumstances of the 

 great Earthquake of December, 1857, by Robert Mallet, C.E., F.R.S., E.G-.S, 

 M.R.I. A., etc., etc. Published by the authority and with the aid of the Royal 

 Society of London. 2 vols. 8vo. Chapman and Sail. 



