drawn in these directions the place of 

 their common intersection must be nearly 

 the place sought"; secondly, from the 

 time of arrival of the earthquake at 

 different places; and thirdly, from the 

 successive arrivals of the great sea-wave. 

 The greatest degree of exactness is ob- 

 tainable " in those cases where earth- 

 quakes have their source from under the 

 ocean, for the proportional distance of 

 different places from that source may be 

 very nearly ascertained by the interval 

 between the earthquake and the succeed- 

 ing wave : and this is the more to be 

 depended on, as people are much less 

 likely to be mistaken in determining the 

 time between two events, which follow 

 each other at a small interval, than in 

 observing the precise time of the happen- 

 ing of some single event" (Arts. 9093). 

 By way of example, the author, making 

 use of his three indications of origin, 

 computed that the focus of the Lisbon 

 earthquake lay under the Atlantic Ocean, 

 c. 33 



