52 Mr. Mautet on the Dynamics of Earthquakes. 
in these convulsions, and of which I felt convinced that a false explanation, so far 
as any, had been previously given. 
I have followed, in the subsequent pages, rather the course of my own pro- 
gress than a strictly systematic arrangement, and shall therefore commence with 
the explanation of the phenomenon above alluded to, and which led me to the 
subsequent investigation and results. 
The phenomenon alluded to, is the displacement of the separate stones of 
pedestals or pinnacles, or of other portions of the masonry of buildings, by the 
motion of earthquakes, in such a manner that the part moved presents evidence of 
having been twisted upon its bed round a vertical axis. This has been hitherto 
attempted to be explained by assuming a vorticose motion to occur. The first 
notice I find recorded of such a peculiar motion is in the Philosophical Transac- 
tions, in an account of the earthquake at Boston, in New England, of November 
18th, 1755, communicated by John Hyde, Esq., F. R. 8. He says: ‘* The 
trembling continued about two minutes. Near 100 chimneys are levelled with 
the roofs of the houses, and many more shattered.” ‘Some chimneys, though 
not thrown down, are dislocated or broken several feet from the top, and partly 
turned round, as on a swivel.” ‘‘ Some are shoved to one side horizontally, jut- 
ting over, and just nodding to fall, &c. &c.’”” This author does not seem to have 
been struck with the odd circumstance of the twisting round of the chimneys, 
and offers no explanation. 
The next instance that I have found is in the account of the great earthquake 
of Calabria, in 1783, as recorded by the Royal Academy of Naples, quoted by Mr. 
Lyell, in his Principles of Geology, vol. i. p. 482, 2nd edit. After describing several 
other remarkable phenomena, tending to show the great velocity of the shock, 
such as, that many large stones were found, as it were, shot out of their beds in 
the mortar of buildings, so as to leave a complete cast of themselves in the undis- 
turbed mortar, while, in other instances, the mortar was ground to powder by 
the transit of the stone, he says: ‘Two obelisks” (of which he has given 
figures), ‘placed at the extremities of a magnificent facade in the convent of 
St. Bruno, in a small town called Stephano del Bosco, were observed to have un- 
dergone a movement of a singular kind. The shock which agitated the building 
is described as having been horizontal and vorticose. The pedestal of each 
obelisk remained in its original place, but the separate stones above were turned 
