Mr. Mauer on the Dynamics of Earthquakes. 55 
“ May it not,” he adds, “be caused by a tendency in each stone to arrange itself 
in some particular position, with respect to the lines of vibration, in a manner 
somewhat similar to pins on a sheet of paper when shaken ?” 
The sagacity of Darwin shewed him that the vorticose hypothesis was 
improbable, and that in order to its being at all tenable, a separate vortex 
must be admitted for every separate stone found twisted, the axis of rotation 
of the vortex having been coincident with that of the stone. Besides this 
paramount improbability, therefore, a little further reflexion would have led 
either Lyell or Darwin to estimate the inconceivable angular velocity of motion 
at the extremity of the radius of one of these vortices, even if assumed at no 
more than a few hundred feet, necessary, in order that. its velocity within a few 
inches of the centre should be so great as to wrench out of its mortared bed, and 
twist, a block of masonry, by merely its own inertia. 
On lately reading the foregoing passage of Darwin, I was soon led to see 
that the twisting phenomenon observed could be readily accounted for upon the 
established principles of mechanics, without having recourse to either vortices 
or vibrations arranging blocks of many hundred weights after the manner of 
pins on paper, or sand on one of Chladni’s acoustic plates, an explanation which 
appears quite as far from probability as its predecessor. 
I assume nothing more than what is universally admitted,—that during earth- 
quakes a motion of some sort takes place, by which the ground itself, and all 
objects resting upon it, are shaken, or moved back and forwards by an alternate 
horizontal motion, within certain narrow limits, which, for all present evidence to 
the contrary, may be a straight line motion, though possibly variable in direction 
at different and sometimes closely successive times, and the velocity of which is 
sufficient to throw down, or disturb the position of bodies supported by the 
earth, through their own inertia. 
If a stone, whether symmetrical or otherwise, rest upon a given base, and that 
motion be suddenly communicated horizontally to that base in any direction, the 
stone itself will be solicited to move in the same direction. The measure of force 
with which the movement of the base is capable of affecting the stone or other 
incumbent body is equal to the amount of friction of the latter upon its base, 
a function of its weight, which, without the intervention of cement, may be 
from one-fifth to one-tenth of the weight of the body, for cut stone resting on 
