'i'^. ' 



464 PHILOSOPHICAL TRANSACTIONS. [aNNO I76O. 



limes when the agitations of the waters were observed in England, if we allovr 

 only a proper interval for the motion to be propagated so far northward, propor- 

 tionably to the time it took up in travelling from its original source near Lisbon. 



These appearances seem to be connected with that mentioned in the preceding 

 article, and they probably may both be accounted for, by supposing a consider- 

 able quantity of vapour to be raised, while the partition before-mentioned was 

 beginning to give way; during which time a partial communication between the 

 water and fire would be brought on, and that by degrees only. Hence the va- 

 pour, not being produced at once but gradually, might creep silently between the 

 strata, towards that quarter where the superincumbent mass of earth was lightest ; 

 and by this means some places very near the source of the vapour might be little, 

 or not at all, affected by it, while others might be greatly affected, though they 

 lay at a great distance; and even those places, which lay immediately over the 

 part where the vapour was passing, might not perceive any effect, on account of 

 the gentleness of the motion occasioned by the small quantity of it. Tliis might 

 continue to be the case, till it came to some country where, the set of strata 

 above being much thinner, the vapour would not only be hurried forward, but 

 collected also into a much narrower compass; and therefore, raising the earth 

 more, would produce more sensible effects; and this we ought chiefly to expect 

 in the most mountainous countries, according to the idea before given of them. 



Sect. 1. — We are told that in the Lisbon earthquake of 17.'>5, " the bar (at 

 the mouth of the Tagus) was seen dry from shore to shore; then suddenly the 

 sea, like a mountain, came rolling in: and about Bellem castle the water rose 50 

 feet almost in an instant: and had it not been for the great bay opposite to the 

 city, which received and spread the great flux, the low part of it must have been 

 under water." The same phenomena were observed to accompany the same 

 earthquake at the island of Madeira: where we are told that at the city of 

 Funchal, " the sea, which was quite calm, was observ^ed to retire suddenly some 

 paces: then rising with a great swell, without the least noise, and as suddenly 

 advancing, it overflowed the shore, and entered the city. It rose full 15 feet 

 perpendicular above high-water mark, though the tide, which ebbs and flows 

 there 7 feet, was then at half ebb. In the northern part of the island the in- 

 undation was more violent, the sea retiring there above 100 paces at first, and 

 suddenly returning, overflowed the shore, forcing open doors, breaking down 

 the walls of several magazines and storehouses, and carrying away, in its recess, 

 a considerable quantity of grain, and some hundred pipes of wine.** 



Both these appearances seem to admit of an easy solution, supposing their 

 cause to lie under the bed of the fx^ean: for in the farther progress of tiie com- 

 munication between the fire and water, the vapour, that is gradually raised at 

 first, will at last begin to raise the roof c \ cr the fire, which being supported by 



