BABBAGE ON THE TEMPLE OF SERAPIS. 203 



cations of its having been stationary. For about 6 inches below 

 the highest perforation of the Modiolse the columns are corroded, 

 as if that point had remained exposed for some time, alternately to 

 the action of wind and water. 



78. The next period in the history of the temple was its gradual 

 elevation. Whether the deposit out of which it was dug covered 

 it up before or after this event, is not perhaps distinctly evident. 

 From the section behind the temple, I am induced to suppose that 

 it preceded the elevation; and the chance of the columns not being 

 overthrown by any sudden rising, would be considerably increased 

 by the support they would derive from having more than one-half 

 their height imbedded in earth. 



79. The preceding conclusions involve no hypothesis, and may 

 be considered as inferences fairly resulting from the specimens col- 

 lected, from the facts observed on the spot, and from the historical 

 evidence of changes which have happened in the neighbourhood of 

 the temple. I shall now proceed to offer some conjectures relative 

 to the causes of the successive changes in the level of the ground on 

 which this temple stands — conjectures which I wish to be considered 

 as entirely distinct from the former part of this communication. 



On examining the country round Pozzuoli it is difficult to avoid 

 the conclusion, that the action of heat is in some way or other the 

 cause of the phsenomena of the change of level of the temple. Its 

 own hot spring, its immediate contiguity to the Solfatara, its near- 

 ness to the Monte Nuovo, the hot spring at the Baths of Nero on 

 the opposite side of the bay of Baias, the boiling springs and ancient 

 volcanos of Ischia on one side and Vesuvius on the other, are the 

 most prominent of a multitude of facts which point to that conclusion. 



The mode by which this heat operates is a question of greater dif- 

 ficulty, and in the absence of sufficient data, it may be enough to 

 point out shortly some of its possible results. 



80. It may be imagined that at a considerable depth below the 

 surface a vast reservoir of melted lava exists, containing highly 

 elastic matter imprisoned within it by the pressure of the superincum- 

 bent strata. The addition of matter supplying this elastic fluid, or 

 the accession of heat, may increase the force, or on the other hand, 

 the expansion or contraction of some portion of the superior strata 

 may cause a fissure through which the melted lava may be forced 

 up by the elastic fluid. In such circumstances, besides the earth- 

 quai<es which will be caused by the rent, and the stream of lava 

 which issues through it, the whole of the strata resting on the fluid 

 lava will slowly subside. The cooling of the lava may fill up the 

 rent and the strata again rise as before, until a renewal of the same 

 cause reproduces a renewal of the same effect. It may here be 

 remarked, that the expulsion of the immense quantity of gaseous 

 matter, which some volcanos are known to throw out, may lower the 

 temperature of the cauldron below, more effectually than the abstrac- 

 tion of the lava which is ejected from it. 



81. Another view of the subject is, that there exists below the 

 ground in the neighbourhood of Pozzuoli cavities containing water 



