WARMTH, AND SMELTING,

13

destroy, the importance of this connection, whether the modern modes adopted for heating be regarded as consisting of any of the innumerable varieties of stoves, hot-air vessels, steam machines, or the more recent contrivances for warming apartments by means of pipes circulating water in a state of ebullition-all are dependent upon the combustion of more or less of ignited matter in the state of fuel.

IV. The most important application of fire, however, is in the smelting of ores, the working of metals, and the carrying forwards those chemical operations on a large scale, for which Great Britain and several other countries are so celebrated. The knowledge of the effect of heat in separating metallic particles from the earthy or other masses in which they might be found embedded, is of the highest antiquity; and from the days of Tubal Cain, "the first instructor of all artificers in iron and brass," to the present time, mankind have attached increasing importance to metallurgic operations, and to the arts depending thereupon. And, not only from the records of the earliest ages, but from almost every section of the globe inhabited by man, whether in a savage or a civilized state, we derive fresh materials for evidence in illustration of the dominion which human industry and ingenuity have sought to establish over the mineral kingdom by the agency of fire. Some particulars relative to the different substances used as fuel, may appropriately close this Chapter.

Of the agents of combustion, as defined by the strict nomenclature of Modern Chemistry, it is not necessary, in this place, to take farther notice than briefly to remark that some of these four substancesoxygen, chlorine, bromine, and iodine-being, almost

in every case, one of the two bodies by the combination of which combustion is produced, and the other matters with which they severally combine being far more numerous, the four just mentioned are distinguished, relatively to the phenomena of combustion, by the name supporters of combustion; while the other body forming the combination with them, whatever it may be, is called a combustible.*

Reverting to less scientific phraseology, it may be remarked, that, whatever substance is either capable of being inflamed, or of remaining in a state of incandescence, may come, in a certain sense, under the denomination of fuel. Hence, certain liquids, as alcohol, oil, &c., with all resinous, bituminous, and fatty matters on the one hand; and on the other, several fossil productions, with the intermediate varieties of structure, and ligneous bodies in general, may be at once referred to, as comprising the classes of bodies commonly used as supporters of combustion. Inflammable fluids, in any place, are more rarely used for the production of heat than of light; and in this country, purely bituminous products are almost as seldom applied, by themselves, to the purposes of firing in some parts of the world the case is widely different. Large quantities of naphtha are obtained on the shores of the Caspian sea; and the inhabitants of Baku, one of its ports, are supplied with no other fuel than that obtained from the naphtha and petroleum, with which the neighbouring country is highly impregnated. In the island of Wetoy, and on the peninsula of Apcheron, this substance is said to be very abundant, supplying immense quantities which

Lardner's Treatise on Heat, p. 355.

AGENTS OF COMBUSTION. .

15

are carried away.* The inhabitants of other parts of the world, in the vicinity of Asphaltum springs, have recourse to the like substances for the purposes as well of cooking as of illumination; for which objects, also, the springs of natural gas are sometimes economically applied.

Among some of the eastern nations, the dung of the camel and other herbivorous animals is carefully collected and dried for fuel. A number of curious particulars illustrative of this fact as regards the Jews, are collected by Harmer.† A similar practice formerly prevailed in some of the midland counties of this kingdom.‡

Animal matter is sometimes, though rarely, used as fuel. The Arabs, however, who dwell in that part of their country bordering on Egypt, must be regarded as forming in some degree an exception to the remark; for they draw no inconsiderable portion of the fuel with which they cook their victuals from the exhaustless mummy-pits, so often described by travellers. The extremely dry state of the bodies, and the inflammable nature of the matters with which they have apparently been saturated, during the process of embalming, render them exceedingly convenient for the above purpose. We have a still more striking instance: wood was formerly so scarce at Buenos Ayres, and cattle so plentiful, that sheep were

* Edin. Phil. Journal, vol. v.

+ It is from the soot collected during the combustion of this fuel that the Egyptians procure sal-ammoniac, by simple sublimation.

The droppings of the cows were collected into heaps, and beaten into a mass with water: then pressed by the feet into moulds like bricks, by regu lar professional persons, called clatters (clodders); then dried in the sun, and stacked like peat, and a dry March for the clat-harvest was considered as very desirable.-Journal of a Naturalist.

actually driven into the furnaces of lime-kilns, in order to answer the purposes of fuel. This fact could hardly have been mentioned as credible, however undoubted, if a decree of the King of Spain, prohibiting this barbarous custom, were not still preserved in the archives of Buenos Ayres.

The inhabitants of the sea-coasts, who happen to be remote from better fuel, or too poor to obtain it, collect sea-weed (Fucus vesiculosus, Linn.) and such like stuff for firing-an indifferent enough material for the purpose, as may readily be supposed. In the Norman Isles, sea-weed is assiduously gathered by the inhabitants, both for fuel and manure: it is called in French varech, and in the Jersey dialect "vraic."*

The most convenient, and happily the most abundant, kinds of fuel known in this and most civilised countries, are peat, dried wood, charcoal, and fossil coal, either in the state in which it is raised from the mine, or in the condition of coke. The history of peat, as immediately coming within the design of the present work, will form the subject of the next Chapter; while wood fuel will be subsequently adverted to, in connection with those vicissitudes to which the iron and other trades in this country were exposed, during their transition from a dependence upon our decaying forests, to those inexhaustible depositories of coal, descriptions of the history, working, and commercial importance of which can scarcely fail to impart a lively interest to the ensuing pages.

* The season of collecting this substitute for coal and firewood is made a season of merriment in Jersey; the times of vraicking are appointed by the island legislature, and then multitudes of carts, horses, boats, and vraickers cover the beach, the rocks, and the water.-Inglis's "Channel Islands,” vol. i. p. 99,

CHAPTER II.

GEOLOGICAL THEORIES.

Interesting character of Geological Science-Extent of knowledge required for successful investigation— Controversies and conflicting theories-Important connexion between Geology and Revelation-Question of progressive developement of Species-Hutton and Werner-Subterranean temperature-Paroxysmal and Cataclysmal Eras of MM. Beaumont, Brongniart, and Cuvier-Jameson's Remarks -Mineral and Mosaical Geologies contrasted— Fairholme Theory of Werner-Tabular view of the positions of Strata-Formations—Gradation of Fossils of vegetable origin.

THE science of Geology, a science still in its infancy, has been pursued of late years with an ardour commensurate to the importance of its bearings in relation to the physical structure of the earth, no less than as developing a series of phenomena of the most striking and interesting character. Nor is the study of this comprehensive subject at present confined in its scientific attractions to divines and philosophers on the one hand, nor on the other hand is it left to miners and metallurgists alone to estimate its practical im

C