94 REPORT—1850. 
the author however limits himself almost wholly to the descriptive character 
which a history of the earth’s superficial changes alone requires, and says 
little of theory, and asI shall have large occasion to refer to him hereafter in 
reference to earthquake catalogues, the present notice of his work may here 
suffice. 
Hoffinan and Kries may also be noticed as German authors on earthquakes. 
In 1843, the Professors H. D. and W. B. Rogers of America commu- 
nicated a paper to the British Association of rather an elaborate character 
upon the phenomena and theory of earthquakes. They adopt Mitchell’s 
view, and suppose the earth-wave an actual fold of the solid crust, produced 
by a lava-wave of translation on the surface of the molten matter beneath. 
They infer from two great earthquakes that this moves at from 27 to 30 
miles per minute, either in nearly straight or in curved lines, according to 
the form and position of the focus or points of volcanic action. 
The sea-waves of earthquakes they suppose to be broad undulations of 
the water moving in the same direction with the pulsation of the crust 
and corresponding in breadth with that of the undulations of the earth’s 
crust; yet these, say they, moved at the rate of 34 miles per minute, in the 
case of the New England earthquake of 1756, and of 5 miles per minute in 
that of Lisbon; astriking inconsistency with the velocity previously assigned 
to the earth-wave. 
The tremor or vibratory jar accompanying the great shock or earth-wave, 
they suppose arises from the crushing of the strata through which the shock 
asses. 
᾿ In 1844 appeared Mr. Scott Russell’s full report upon sea and other waves, 
the laws developed in which as to the motions of waves of translation had an 
important effect upon the immediately subsequent advance towards a com- 
plete and true theory of earthquake phenomena. 
In February 1846, the author's paper upon the dynamics of earthquakes 
was read to the Royal Irish Academy, and published in vol. xxi. part 1 of 
the Transactions of that Academy, in which the first attempt was made to 
establish upon strict physical bases a theory that should embrace and account 
for all the recorded phenomena of earthquakes, both on land and sea. How 
far he has succeeded in this, futurity must decide. 
In June 1847, Mr. Hopkins produced his report on the theories of ele- 
vation and earthquakes (Trans. Brit. Assoc.). The principal features of 
this paper are, a digest of his previously published mathematical papers 
on the formation of fissures, &c. by elevations and depressions; a popular 
résumé of the acknowledged laws of formation and propagation of elastic and 
fluid waves, and the partially placing in a mathematical dress the author's 
theory of earthquake motions as developed in the paper last alluded to; to 
this is to be added a demonstration of a method for finding analytically the 
depth of the centre of disturbance, from observations made with a seismometer, 
such as that described by the author. (Trans. Roy. Irish Acad. vol. xxi.) 
I have thus brought the literature of earthquakes down to the present 
time; in doing so I would not be misunderstood as attempting a complete ac- 
count thereof, but such merely as is sufficient to mark the progress of human 
knowledge of our subject ; I have therefore omitted to notice the able résumés 
of such literature given by Sir C. Lyell (Prin. Geol. chap. 28 to 33), and by 
several other authors. Neither have I at all adverted to the works of authors 
writing specially of volcanoes, as, although connected with our subject, not 
_ properly belonging to it. 
I now proceed to the more immediate subject of this Report. 
