336 Conjectures concerning the Cause, and Observations 
prehended within the space of two or three minutes; possibly, 
however, some of the earthquakes, which we have had in Eng- 
land, may have been of this class. 
Section VII.—90. If we would inquire into the place of the 
_ origin of any particular earthquake, we have the following grounds 
to go upon, 
91. First, The different directions, in which it arrives at se- 
_veral distant places: if lines be drawn in these directions, the 
.place of their common intersection must be nearly the place 
sought: but this is liable to great difficulties; for there must 
necessarily be great uncertainty in observations, which cannot, at 
best, be made with any great precision, and which are generally 
made by minds too little at ease to be nice observers of what 
passes ; moreover, the directions themselves may be somewhat 
-varied, by the inequalities in the weight of the superineumbent 
matter, under which the vapour passes, as well as by other 
causes. 
92. Secondly, We may form some judgement concerning the 
place of the origin of a particular earthquake, from the time of 
its arrival at different places; but this also is liable to great dif- 
-ficulties, In both these methods, however, we may come to a 
much greater degree of exactness, by taking a medium amongst a 
variety of accounts, as they are related by different observers, But, 
93. Thirdiy, We may come to the greatest degree of exact- 
ness in those cases, where earthquakes have their source from 
under the ocean; for, in these instances, the proportional di- 
stance of different places from that source may be very nearly 
ascertained, by the interval between the earthquake and the suc- 
ceeding wave: and this is the more to be depended on, as_peo- 
ple are much less likely to be mistaken in determining the time 
between two events, which follow one another at a small interval, 
than in observing the precise time of the happening of some 
single event. 
94, Let us now, by way of example, endeavour to inquire into 
the situation of the cause, that gave rise to the earthquake of 
the Ist of November 1755, the place of which seems to have been 
under the ocean, somewhere between the latitudes of Lisbon and 
Oporto, (though probably somewhat nearer to the former) and at 
the distance, perhaps, of ten or fifteen leagues from the coast. For, 
95. First, The direction, in which the earthquake arrived at 
Lisbon, was from the north-west ; at Madeira it came from the 
north-east; and in England it came from the south-west ; all of 
which perfectly agree with the place assumed* . 
96. Se- 
* All these directions together with the times when the earthquake, as 
well as the succeeding wave, arrived at different places, (two or three only 
excepted) 
a) 
