VOL. LI.] PHILOSOPHICAL TRANSACTIONS. 463 



increase in height, till it becomes too tall in proportion to its thickness to bear 

 any longer the pressure of the melted matter; which mast necessarily happen at 

 last, because its thickness will not exceed a certain limit. Besides the giving 

 way of tliis wall, the fire may undermine the space containing the water, and by 

 that means open a communication between them. Let us suppose one of these to 

 come to pass, and the time arrived when the partition begins to yield. If then 

 the water had any way to escape readily, the breach would be made, and the 

 melted matter would burst forth immediately, and flow out in large quantities at 

 once among it; but as this is not the case, and it can only escape by 'oozing 

 slowly between the strata, and through the fissures, the way that it came, the 

 breach will be made gradually ; whence we may account for some appearances 

 that have preceded great earthquakes. 



We are told that 2 or 3 days before an earthquake in New England, the 

 waters of some wells were rendered muddy, and stunk intolerably; why might 

 not this be occasioned by the waters contained in the spaces before described, 

 which, being impregnated with sulphureous steams, were driven up, and mixed 

 with the waters of the springs? At least, there can be no doubt, by whatever 

 means it was brought about, that this phenomenon was owing to the same cause, 

 already beginning to exert itself, which afterwards gave rise to the succeeding 

 earthquake. 



Something like this happened before the Lisbon great earthquake of 1755. 

 We are told, that at Colares, about 20 miles from it, " in the afternoon pre- 

 ceding the 1st of November, the water of a fountain was greatly decreased; on 

 the morning of the 1st of November it ran very muddy, and after the earth- 

 quake it returned to its usual state, both in quantity and clearness." The same 

 author says, a little lower, " in the afternoon of the 24th, I was much appre- 

 hensive that the following days we should have another great earthquake; for I 

 observed the same prognostics as in the afternoon of Oct. 31, that is," &c. 

 " And I further observed that the water of a fountain began to be disturbed to 

 such a degree, that in the night it ran of a yellow clay colour; and from mid- 

 night to the morning of the 25th I felt 5 shocks, one of which seemed as vio- 

 lent as that of the 1 1th of December." But the most extraordinary appearance 

 of any that preceded this earthquake was that of the agitation of the waters of 

 Lochness, and some others of the lochs in Scotland, about half an hour before 

 any motion was felt at Lisbon, though the cause of all these great effects could 

 not lie far from thence, and certainly lay to the south of Oporto. Nor is it pro- 

 bable that there should be any mistake in the time, not only because the dif- 

 ference is too great, as well as the concurrent testimonies too many, to admit of 

 such a solution , but because they mention another greater agitation that hap- 

 pened about an hour and half after the former; which latter agrees with the 



