第25章

In February, 1829, a still more striking experiment was made in the yard of the barracks of St.Gervais.Two towers were erected two stories high, and were surrounded with heaps of inflamed materials consisting of fagots and straw.The firemen braved the danger with impunity.In opposition to the advice of M.Aldini, one of them, with the basket and child, rushed into a narrow place, where the flames were raging 8 yards high.The violence of the fire was so great that he could not be seen, while a thick black smoke spread around, throwing out a heat which was unsupportable by spectators.The fireman remained so long invisible that serious doubts were entertained of his safety.He at length, however, issued from the fiery gulf uninjured, and proud of having succeeded in braving so great a danger.

It is a remarkable result of these experiments, that the firemen are able to breathe without difficulty in the middle of the flames.This effect is owing not only to the heat being intercepted by the wire-gauze as it passes to the lungs, in consequence of which its temperature becomes supportable, but also to the singular power which the body possesses of resisting great heats, and of breathing air of high temperatures.

A series of curious experiments were made on this subject by M.Tillet, in France, and by Dr.Fordyce and Sir Charles Blagden, in England.Sir Joseph Banks, Dr.Solander, and Sir Charles Blagden entered a room in which the air had a temperature of 198 degrees Fahr., and remained ten minutes; but as the thermometer sunk very rapidly, they resolved to enter the room singly.Dr.Solander went in alone and found the heat 210 degrees, and Sir Joseph entered when the heat was 211 degrees.

Though exposed to such an elevated temperature, their bodies preserved their natural degree of heat.Whenever they breathed upon a thermometer it sunk several degrees; every expiration, particularly if strongly made, gave a pleasant impression of coolness to their nostrils, and their cold breath cooled their fingers whenever it reached them.On touching his side, Sir Charles Blagden found it cold like a corpse, and yet the heat of his body under his tongue was 98 degrees.Hence they concluded that the human body possesses the power of destroying a certain degree of heat when communicated with a certain degree of quickness.This power, however, varies greatly in different media.

The same person who experienced no inconvenience from air heated to 211 degrees, could just bear rectified spirits of wine at 130 degrees, cooling oil at 129 degrees, cooling water at 123 degrees, and cooling quicksilver at 118 degrees.A familiar instance of this occurred in the heated room.All the pieces of metal there, even their watch-chains, felt so hot that they could scarcely bear to touch them for a moment, while the air from which the metal had derived all its heat was only unpleasant.M.Duhamel and Tillet observed, at Rochefoucault in France, that the girls who were accustomed to attend ovens in a bakehouse, were capable of enduring for ten minutes a temperature of 270 degrees.

The same gentleman who performed the experiments above described ventured to expose themselves to still higher temperatures.Sir Charles Blagden went into a room where the heat was 1 degree or 2 degrees above 260 degrees, and remained eight minutes in this situation, frequently walking about to all the different parts of the room, but standing still most of the time in the coolest spot, where the heat was above 240 degrees.The air, though very hot, gave no pain, and Sir Charles and all the other gentlemen were of opinion that they could support a much greater heat.During seven minutes Sir C.Blagden's breathing continued perfectly good, but after that time he felt an oppression in his lungs, with a sense of anxiety, which induced him to leave the room.His pulse was then 144, double its ordinary quickness.In order to prove that there was no mistake respecting the degree of heat indicated by the thermometer, and that the air which they breathed was capable of producing all the well-known effects of such a heat on inanimate matter, they placed some eggs and a beef-steak upon a tin frame near the thermometer, but more distant from the furnace than from the wall of the room.In the space of twenty minutes the eggs were roasted quite hard, and in forty-seven minutes the steak was not only dressed, but almost dry.Another beef-steak, similarly placed, was rather overdone in thirty-three minutes.In the evening, when the heat was still more elevated, a third beef-steak was laid in the same place, and as they had noticed that the effect of the hot air was greatly increased by putting it in motion, they blew upon the steak with a pair of bellows, and thus hastened the dressing of it to such a degree, that the greatest portion of it was found to be pretty well done in thirteen minutes.

Our distinguished countryman, Sir F.

Chantrey, has very recently exposed himself to a temperature still higher than any which we have mentioned.The furnace which he employs for drying his moulds is about 14 feet long, 12 feet high, and 12 feet broad.When it is raised to its highest temperature, with the doors closed, the thermometer stands at 350 degrees, and the iron floor is red hot.The workmen often enter it at a temperature of 340 degrees, walking over the iron floor with wooden clogs, which are of course charred on the surface.

On one occasion Sir F.Chantrey, accompanied by five or six of his friends, entered the furnace, and, after remaining two minutes, they brought out a thermometer which stood at 320 degrees.Some of the party experienced sharp pains in the tips of their ears, and in the septum of the nose, while others felt a pain in their eyes.