VOL. LT.] PHILOSOPHICAL TRANSACTIONS. 471 



from which he coiriputed, at the distance of Lisbon "2^!. 3 . . 12 



about a degree of a great circle from Lisbon, Oporto 3 . . 5 . . 



^ f r-» . T Ayamonte .... 6 . . . . 53 



and a degree and a halt h'om Oporto. In con- Cadiz 9 . 12 . . 82 



sequence of this supposition, he added 3 mi- Madrid 9 .. u •• 



^ , . -V 1 • 1 1 Gibraltar 11 .. 18.. 



nutes to the mterval between the time when the Madeira 19 . . 25 . . 152 



shock was felt at Lisbon, and at the several Mountsbay.. . . 20 .. . . 267 



, rr^i .' . 1 • .u i. ui Plymouth 21 .. ..360 



other places. 1 he hrst column in the table Portsmouth 23 . . 29 . . 



contains the names of places ; the 2d, the dis- Kingsale 23.. ..290 



^ , , . ^ 1 1 • I ir Swansea 24.. .. 530 



tances from the assumed point, reckoned in halt -p^e Hague. 30 . . 32 . . 



den-rees; the 3d, the time that the earthquake Lochness 33.. 66 .. 



,, . . 11 .u u J • • Antigua 98 . . ..565 



took Up in travelhng to each, expressed in mi- Barbadoes 101 .. ..485 



nutes ; and the 4th contains the time in which 



the wave was propagated from its source to the respective places, expressed in 



minutes likewise. 



In computing the times in this table, allowance was made for the difference 

 of -longitude, as it is laid down in the common maps, which are not always 

 greatly to be depended on. The times themselves also are often so carelessly ob- 

 served as well as vaguely related, that many of them are subject to considerable 

 errors ; the concurrent testimonies however are so many that there can be no 

 doubt about the main point ; and that the errors might be as small as possible, 

 Mr. M. not only endeavoured to select those accounts that had the greatest ap- 

 pearance of accuracy, but, in all cases where it was to be had, always took a 

 mean among them. In many of the accounts the relaters say only between 

 such hours, or about such an hour. 



It is observable, in the preceding table, that the times which t4ie wave took 

 up in travelling are not in the same proportion with the distances of the res- 

 pective places from the supposed source of the motion ; this however is no ob- 

 jection asjainst the point assumed, since it is manifest, wherever it was, that it 

 could not be far from Lisbon, as well because the wave arrived there so very 

 soon after the earthquake as because it was so great, rising, as we are told, at 

 the distance of 3 miles from Lisbon to the height of 50 or 60 feet. The true 

 reason of this disproportion seems to be the difference in the depth of the water; 

 for, in every instance in the above table, the time will be found to be propor- 

 tionably shorter or longer as the water through which the wave passed was 

 deeper or shallower. 



Sect. 8. — If we would inquire into the depth at which the cause lies that 

 occasions any particular earthquake, Mr. M. knows of no method of determining 

 it, which does not require observations not yet to be had ; but if such could be 

 procured, and they were made with sufficient accuracy, he thinks some kind of 

 guess might be formed concerning it : for, 1st, in those instances where the 



