manifold. To a few evident causes, however, they may in general be attributed, though they cannot in any manner be proved. First, to heat, which melts, volatilizes, mixes, combines, calcines, vitrifies, and consequently gives birth to fiery eruptions. Secondly, to water, which may be said to be the most universal, as it searches every where. Thirdly, to air, which by its currents, forms the winds, which, pent up in carverns, and rarefied by heat, burst through every thing that opposes them; break out caverns and open those mouths, whence issue forth inevitable destruction. And fourthly, to substances of a saline nature, which greatly assist inflammation.

Beyond this, it is chimerical to go. We cannot comprehend, says Aristotle, the integral parts of nature. Those who have pretended to that knowledge, have only exhibited weakness and contradiction. To explain the properties of fire, some have said, the parts must be pyramidal; others obeliscal; others spherical. All we can arrive at, are the apparently certain elements, which have in themselves an inherent property of motion and of rest. Thus, says he, material earth tends towards the centre; water rises above

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the earth; air above the water; and fire above the air. The intermediate water and air, hold only a relative place, being more light than earth, but more ponderous than fire.

LETTER

LETTER XXXVIII.

i

AFTER a long journey, wherein we have unavoidably been obliged to look with more than common attention, at each of the elementary features of nature, we at length get to a point, whence the whole collective force is to be viewed; and where even in the pride of present beauty, former discord, and the rage of contending elements, are to be observed in their most hideous forms. The glory of light, and the energy of fire, have amply been displayed before us. The creative powers of the waters, have likewise manifested themselves in our examination. But, we are now to contemplate nature as undergoing an awful change. The agents of existence, we shall now find the engines of destruction. That which warmed the hearts of mortals with the liveliest throbs of gratitude, now shall appal them with terror and apprehension. Instead of life, we shall have death. Instead of harmony, we shall have convulsions and desolation,

The combustible matters in nature, are divided into five kinds, independent of phosphora, which might be added. The diamond; the inflammable gaz; sulphur; metallic substances, and bitumens: and all have the same property of burning, when roused by the contact of air. There are three sorts of combustion. With flame and heat as sulphur; without flame as many metals; and with flame but without heat, as phosphorous. The diamond, of all these, is the most infusible, most fixed, most transparent, most divested of smell, and is perhaps the body most inflammable that is known; as it burns entirely away, and leaves no residuum. Sir Isaac Newton called it a coagulated inflammable substance. But diamonds, which in fact seem to be no other than particles of light, bound up in adamantine chains, from their apparent resemblance to crystaline, and vitrifiable stones and gems, were universally held by naturalists, not to be different in their constituent matter from such stones and gems, except in a greater degree of purity. Newton, however, judging by their refractive power, classed them with inflammable bodies; and held, that they consisted of the purest phlogiston; but according to the custom of his time, he used the words sulphurous, unctuous, &c. to signify what later chymical writers express by the terms phlogistic, or hydrogenous: he accordingly says, a diamond is probably an unctuous substance coagulated. From experiment indeed it appears, that diamonds are the only natural substance, in which phlogiston appears to exist pure and unmixed. * For all inflammable liquors contain water: and all solid inflammable bodies leave a residuum of ashes or coal. Diamonds dissipate and totally disappear, while the ruby and the other gems sustain the operation of heat without damage. Thus, from their native form and constituent matter, they may probably perhaps be defined crystalized phlogiston.

The opinions of philosophers have varied with the varied revolutions of science; and they have scarcely ever long together held to the same point. Thus, they have differed as to the formation of combustible matters. It at length, however, seems to be generally believed, that those even in the bowels of the earth, such as coal and bitumens, are the product of organized bodies which have vegetated on the surface of it. Many proofs might be adduced, that pit-coal in particular, is composed of the spoils