604 PHlLOSOPHieAL TRANSACTIONSWi [anNO J 762. 



than 6. On November 1, 1755, the day the earthquake happened at Lisbon, 

 there was then here, in this same manner, an agitation of the water.' 



At Fyal island, one of the Azores, and Terceira, the sea rose to a great 

 height, and fell again so low that the quays were left dry; all the lighters and 

 ^hing-boats that were hauled up in Portorico, were carried down into the bayj 

 and broken to pieces on the rocks. About a fortnight after, several earthquakes 

 (successively more and more violent) ended not, till on the 20th 3 volcanos 

 threw out as many rivers of lava, of near a mile in breadth, and 4 yards high, 

 which threatened desolation to the whole country, and continued over-running 

 «very tree and house till the 24th. 



From these accounts the violence of this earthquake was greatest at, or rather 

 near Lisbon ; perhaps at sea, in latitude between 43 and 44, and longitude 

 about 11° 19', where no tremors of land could be observed, and consequently 

 the effects not so terrifying, nor perceived by so many, nor so destructive as if 

 it had happened on the land, and contiguous to Lisbon, as that of 1755. The 

 weather various in the different places, but mostly calm. 



There was a great conformity between the effects of the earthquake of Nov. 

 1, 1735, and of this of March 31st, 1761 ; viz. in the extent; in the rise of 

 the waters ; in the calmness of the weather in most parts ; and in the succession 

 of time, beginning sooner at Lisbon than on the northern shores both times. 



LXFL Observations on a Clock of Mr. John Sheitorif made at St. Helena. By 

 the Rev. Nevil Maskelyne, M. A.^ F. R. S. p. 434. 



The ancients were well acquainted with the rotundity of the earth, and were 

 satisfied, that heavy bodies, in every place, had a tendency to its centre : but 

 they had never any suspicion that the force of their tendency to the centre was 

 greater in one country than another, or that when dropped from any height they! . 

 fell faster in one latitude than another. 



The great Huygens, who first set the doctrine of centrifugal forces in a clear 

 light, saw plainly that the weight of bodies must naturally be less at the equator 

 than at the poles ; their great velocity there round the earth's axis taking off part 

 of the weight which they acquire by their gravitation towards the earth's centre. 

 And though he was not quite exact in settling the true proportion of the force 

 of gravity in different latitudes; yet we owe this obligation to him, of having 

 made the first discovery of a thing, which has since been the ground of so many 

 theories and experiments. Mr. Richer, when he went to the island of Cayenne, 

 made the first experimental proof of the decrease of gravity, in approaching the 

 equator, though he was not led to it by Huygen's theory, which was then but 

 lately published, and not so generally known; but from finding his clock, which 



