Page:Great Neapolitan Earthquake of 1857 Vol 2.djvu/378

Rh, and lowest portion, of the cavity—the total accumulated pressure upon its lamellar walls, of 27 geographical square miles in area, would be more than 640,528 millions of tons.

And yet, it is extremely doubtful, that the temperature of the focal cavity, was not very much higher. The probable superior limit, of temperature, would be that it might be as high, as that of the "foyer" of Vesuvius.

I cannot find, that any professed investigator of volcanoes, has ever thought of making, the very obvious and important experiment, of lowering, with an iron wire a pyrometer, as far as possible, into a crater, in order to get some idea, of its actual temperature, even within a few score yards of its mouth.

When on Vesuvius, on the occasion of this Report, I feel satisfied that I could have so measured the temperature, of the minor mouth, then in powerful action, to the depth of several hundred feet, had I possessed the instrumental means at hand. To this smaller mouth, it was then possible, by wrapping the face in a wet cloth, to approach so near, upon the hard and sharply defined (though thin and dangerous) crust of lava, through which it had broken, as to see its walls, for quite 150 feet down, by estimation. They were glowing hot, to the very lips, although constantly evolving, a torrent of rushing steam, with varying velocity. Accustomed as I have been, by profession, for years, to judge of temperatures in large furnaces, by the eye, I estimated the temperature of this mouth, by the appearance of its heated walls, at the lowest visible depth; they were there, of a pretty bright red, visible in bright winter sunlight overhead. I have no doubt, then, that the temperature of the