In the book 'A Voice from St.Helena' ( Redfield, vol II, 1854) from Barry E. O'Meara I read on pag. 132 - 133 following:
On the 21th sept. 1817:
At about six minutes before ten o’clock at night, three distinct shocks of an earthquake were felt at Longwood. The whole of the house was shaken with a rumbling, clattering noise at first, as if some heavy body, like a loaded wagon, was dragged along the upper apartments, succeeded by an evident tremulous motion of the ground, the glasses ratling on the table, and the pictures receding from the walls. The duration of the whole might have been from sixteen to twenty seconds, as Captain Blakeny and myself, who were sitting together at the time that it occurred, had sufficient time from its commencement until it was over, to reason and reciprocally ask from what it could proceed, before we guessed at the right cause, which we discovered simultaneously before it ceased. No mischief was done. *
Generals Montholon, Gourgaud, all the household attendants and English servants came out. No alarm appeared to exist amongst them.
General Montholon informed, that his son Tristan, who was asleep, was awoke by the shock, and exclaimend that somebody was endeavoring to throw him out of the bed.
General Gourgaud also felt three distinct shocks. Upon inquiry being made of some of the sentinels about the house, they replied that they had not experienced any thing extraordinary. This may be accounted for by the fact of the wind having been so strong at the time, that they were obliged to use considerable exertion in walking against it.
The sensation was very strongly felt in our kitchen, about forty yards from the house, and at the guard-room, about five hundred yards distant, particularly by those men who were lying down on the ground.
Very little mischief was done in the island. It appeared that the direction of the shocks was perpendicular. Had it been lateral, Jamestown must have been overwhelmed with immense masses of rock.
* Although Napoleon was in bed, which he did not leave during the time of the shocks, some veracious person wrote in England that “Bonaparte endeavored to escape out of the house, but was stopped by the sentinels” , which falsehood was eagerly inserted in some of the ministerial papers.