The explanation of this phenomenon seems to be, that on the rising of the bell the pressure on the air within being diminished by a weight equal to several feet of water, it began to expand; and some portion of it escaping under the edges of the bell, reduced the temperature of that which remained so much, that it was unable to retain, in the state of invisible vapour, the water which it had previously held in solution. Thus the same principle which constantly produces clouds in the atmosphere filled the diving-bell with mist.
〈SUBMARINE NAVIGATION.〉
This first led me to consider the much more extensive question of submarine navigation. I was aware that Fulton had already descended in a diving-vessel, and remained under water during several hours. He also carried down a copper sphere containing one cubic foot of space into which he had forced two hundred atmospheres. With these means he remained under water and moved about at pleasure during four hours.
〈OPEN SUBMARINE VESSEL.〉
But a closed vessel is obviously of little use for the most important purposes to which submarine navigation would be applied in case of war. In the article Diving Bell, published in 1826, in the ‘Encyclopedia Metropolitana,’ I gave a {212} description and drawings of an open submarine vessel which would contain sufficient air for the consumption of four persons during more than two days. A few years ago, I understand, experiments were made in the Seine at Paris, on a similar kind of open diving-vessel. Such a vessel could be propelled by a screw, and might enter, without being suspected, any harbour, and place any amount of explosive matter under the bottoms of ships at anchor.
Such means of attack would render even iron and iron-clad ships unsafe when blockading a port. For though chains were kept constantly passing under their keels, it would yet be possible to moor explosive magazines at some distance below, which would effectually destroy them.
CHAPTER XVI. EXPERIENCE BY FIRE.
Baked in an Oven — A Living Volcano — Vesuvius in action — Carried up the Cone of Ashes in a Chair — View of the Crater in a Dark Night — Sunrise — Descent by Ropes and Rolling into the great Crater — Watched the small Crater in active eruption at intervals — Measured a Base of 330 feet — Depth of great Crater 570 feet — Descent into small Crater — A Lake of red-hot Boiling Lava — Regained the great Crater with the sacrifice of my Boots — Lunched on Biscuits and Irish Whisky — Visit to the Hot Springs of Ischia — Towns destroyed by Earthquake — Coronets of Smoke projected by Vesuvius — Artificial Mode of producing them — Fire-damp visited in Welsh Coal-mine in company with Professor Moll.
Baked in an Oven.
CALLING one morning upon Chantrey, I met Captain Kater and the late Sir Thomas Lawrence, the President of the Royal Academy. Chantrey was engaged at that period in casting a large bronze statue. An oven of considerable size had been built for the purpose of drying the moulds. I made several inquiries about it, and Chantrey kindly offered to let me pay it a visit, and thus ascertain by my own feelings the effects of high temperature on the human body.