62 Original Articles. [Jan. 
as well as the temperature, of the formations within our earth, to a depth 
far more profound than can be reached by any other mode of investi- 
gation, or directly ever reached at all, and that by its means, we may 
acquire some knowledge of the formations constituting the beds, or 
situated even far beneath the beds, of the great oceans. These are, in 
fact, the great aims of Seismology, for the investigation of Earthquakes 
is only a means to an end. 
This paper drew the attention of physicists and geologists, in a 
prominent manner, to the subject of Earthquakes, and was followed 
by several reports drawn up by desire of the British Association, and 
published in its volumes; and also by the laborious task completed 
in 1858, of drawing up and discussing the ‘ British Association Harth- 
quake Catalogue.’ For this large body of seismic statistics, embracing 
all historic time and the whole earth’s surface, and numbering more 
than 6,000 Earthquakes, the groundwork had been laid by the immense 
and valued labours in the same direction of Von Hoff, and of M. Perrey 
of the Faculty of Sciences of Dijon, whose life has been devoted to 
this branch of the subject, and whose labours are still continued with 
the enthusiasm and success of his early youth, 
Since 1846, the experimental method has been brought to bear 
upon the subject; and the observations made on natural shocks have 
been compared with those of Earthquakes artificially produced. And 
now Seismology has taken an acknowledged place as an important and 
productive branch of Cosmical Physics, and already some able men in 
different quarters of Europe are pursuing its study. Amongst those 
who have most, and most recently, advanced our knowledge, are 
Haughton, Favre, Schmidt Jeittelles, Otto Wolger, and Kluge. But 
we have now brought the history of discovery in Seismology to such a 
point, that its further development will best merge into the remarks to 
follow, upon the doctrines and facts of the Science itself. 
Recurring now to the definition already given of an Harthquake, 
we will clear our ideas as to what it means. The shock is produced 
by a wave of elastic compression passing through some portion of the 
substance of our earth. Elasticity is that property in matter which 
tends to the restoration of igure in solids, and of volume in liquids 
and gases, when altered by an extraneous force ; and every different 
substance has its own co-efficient (or measure) of elasticity of volume 
(cubic elasticity), and of elasticity of form (linear elasticity). 
In common parlance, it is often confounded with flexibility. Thus, 
when people praise the springs of an easy-going carriage by saying, 
“ they are so elastic,” they mean they are so flexible. Elasticity and 
flexibility are, in fact, opposites in some respects. A perfectly elastic 
solid is one that, after forcible alteration of figure completely restores 
itself ; if perfectly flexible, it would not restore itself at all, and 
might be bent to any extent without disruption. No such bodies 
exist in nature. All terrestrial materials present variable combi- 
nations of elasticity and flexibility, neither being perfect. Thus, 
Glass, Ivory, Agate, and Hard Steel are highly elastic bodies, but very 
slightly flexible. They break, as we all know, if but slightly bent, or 
