blessed with a knowledge of the true origination of mankind, and their earliest history, should condescend to such poor conjectures, is a symptom of present infidelity and approaching barbarism. The first family placed by the Creator upon this earth offered sacrifices; which being an article of religious duty, they were certainly possessed of the means of performing it, and consequently of the knowledge and use of fire, without which it could not be practised. The next generation presents us with artificers in brass and iron, which could not possibly be wrought without the complete knowledge of fire; neither indeed could any works of art be well carried on, The account of this affair in the Bible is much more natural, because it is more agreeable to the goodness of God, and the dignity of the human species, than to suppose, on the principles of a wild and savage philosophy, that men were left ignorant of the use of an element intended for their accommodation and support. To interdict a man from the use of fire and water, was accounted the same in effect as to send him out of life; so that if men, upon the original terms of their creation, were thus. interdicted by the Creator himself, as the

heathen

heathen mythologists supposed them to be, they were sent into life upon such terms as others were sent out of it. If we admit any one such gloomy supposition, where shall we stop? If mankind were left destitute in respect to the knowledge of fire, perhaps they were left without language, without food, without clothing, without reason, and in a worse condition than the beasts, who are born with the proper knowledge of life, but man receives it by education; therefore he who taught the beasts by instinct, taught man by information. This digression having a near relation to our present subject, and particularly to this part of it, the reader, I hope, will excuse me for going into it. If the knowledge of fire could ever possibly be lost by any people of the earth, degenerating into gross stupidity and barbarism, it is not impossible that time and chance might recover it, though these are but very indifferent principles to trust to. Gunpowder was discovered, as we say, by chance; but mankind had spent above five thousand years on earth before they fell upon it. Sanchoniatho, in his Phoenician History, relates a circumstance of trees taking fire when their branches were rubbed together with the wind:

and

and Avicenna, the Arabian physician, tells us, that a sort of cane, which the Indians use for their lances, has been set on fire, when the canes, while growing and very dry, were rubbed hard one against another with the violence of the wind *. In some parts of the globe fire offers itself spontaneously to the use of man, as at Baku in Persia, where naptha takes fire of itself from the ground, and is applied by the inhabitants to domestic purposes †.

Fire will manifest itself without being excited either by percussion or attrition: a burning heat frequently arises from cold materials in such masses of matter as consist of heterogeneous principles combined together. If a large quantity of hay is laid together in too moist a state, it will by degrees take fire, which seems to happen for the following obvious reasons: it is certain that the subtile matter of fire is at all times circulating through the porous substance of bodies, and expelling the moisture which is lodged within them, in the form of vapour, which is sometimes visible, but in many cases so slowly excited as to be invisible, like the insensible perspi

VOL. IX.

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* Phil. Trans. vol. lvii. No. II.

+ See Mr. Hanway's Travels.

perspiration of the animal frame. This vapour being excited within the recesses of the mass, and being unable to escape through the pores of the incumbent matter, so fast as it arises, it is returned back upon itself, and its agitation is thereby very much increased, the natural consequence of which is an attrition of the parts, producing an intestine heat. At the same time, a large quantity of air is generated, which adds much to the expansive force; and while these causes are at work, the whole matter is sinking with its own weight into a lesser compass, by means of which the fire and air being strongly compressed, are excited still to farther degrees of commotion, till they break out into actual flame, and consume the substance. The pressure of the air and vapour from the incumbent weight, has a great share in this effect. When loose gunpowder is fired, it is easily dissipated with little explosion, and may almost be said to evaporate; but when it is confined and compressed, the force of the explosion is very much increased; and the case is much the same when the vapour of boiling water is confined: from which examples, it is easy to imagine what a commotion will arise, when the steam of ferment

ing vegetables is strongly compressed. What happens to a stack of hay, will also happen to an heap of coals, when they are laid up too moist in a very large quantity, and in a close place. An intestine heat will be raised, breaking out at length into an actual fire. From the great quantity of the fuel, so intense is the heat when a large stack of hay is on fire, that the substance of the hay is turned into glass. I have some lumps of this vitrified matter, with the stalks of hay appearing in some parts of them like the needles of antimony; they were found among those ashes that fell from the heart of the fire, after a conflagration, in which forty loads were consumed *.

We have another way of obtaining fire, by exciting it to activity in such bodies as retain it long in a fixt or quiescent state. There are many of these, and of different sorts, some solid, some fluid, some natural, some artificial; all of which may be called phosphori, or substances retaining the matter of light within them, as the sponge retains water. Some phosphori are very conspicuous, others obscure and almost equivocal, of

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* The same effect is related in the Dissertationes Physica of Paulus Casatus, the Venetian. Diss. 7. p. 212.