Mineralogy and Geology. 271 
motion is sufficient, if the centre of adherence, in the stone to be 
moved, is not directly under the centre of gravity. This is proved by 
simple trial. With regard to the possibility of restoring of the stone 
to its original position by the backward move of an earthquake vibra- 
iy _ tion, he argues that the forward and backward action are not equal, 
as the force producing the earthquake is usually progressive in one di- 
rection; and further, the new condition of the stone, after. the first 
motion, renders it scarcely possible that the reverse motion, however, 
nearly the same, could exactly neutralize and return the stone to its 
former place. 
The following are some instances of this peculiar motion mentioned 
88 on record. 
_ “The first notice I find recorded of such a peculiar motion, is in the 
Philosophical Transactions, in an account of the earthquake at Boston, 
in New England, of November 18th, 1755, communicated. by John 
Hyde, Esq., F.R.S. He says, ‘the trembling continued about two 
minutes; near one hundred chimneys were levelled with the roofs of 
the houses, and many more shattered. Some chimneys, though not 
thrown down, were dislocated or broken several feet from the top, and 
partly turned round-as on a swivel. Some are shoved to one side hor- 
izontally , jutting over, and just nodding to fall” &c. This author 
_ does not seem to have been struck with this odd circumstance of the 
twisting round of the chimneys, and offers no explanation. The next 
- Instance that I have found is in the aceount of the great earthquake of 
‘Calabria, in 1783, as recorded by the Royal Academy of Naples, quot- 
ed by Mr. Lyell, in his Principles of Geology, vol. i, page 482. After 
ri ing several other remarkable phenomena, tending to show the 
_ Seat velocity of the shock, such as that many large stones were found, 
— aSit were, shot out of their beds in the mortar of buildings, so as to 
ce leave 2 complete cast of themselves in the undisturbed mortar ; while 
iN’ other instances the mortar was ground to powder by the transit of 
~ the’ stone, he says, ‘'I'wo obelisks (of which he has given figures) 
Placed at the extremities of a magnificent fagade in the convent of St. 
Bruno, in.a small town called Stephano del Bosco, were observed to 
have undergone a movement of a singular kind. The shock, which 
Agitated the building, is described as having been horizontal and vorti- 
_ 608e.. The pedestal of each obelisk remained in its original place, but 
the separate stones above were turned partially round, and removed 
_ Sometimes nine inches from their.position without falling.’ 
|. od Dave: found: some.few. other notices of similar phenomena in old 
books of travels. ‘Two additional instances, however, will be sufficient. 
The first will be-found in the quarterly journal of the Royal Institution, 
_ M)@narrative of the earthquake in Chili, of November, 1822, commu- 
