them, and those strike best which abound most in them. For these scintillations are not the accension of the air, upon the collision of two hard bodies, but rather the inflammable effluencies or vitrified sparks discharged from the bodies collided. For diamonds, marbles, heliotropes, and agaths, though hard bodies, will not readily strike fire with a

as soon as the body is a little violently heated." That such is truly the nature of such sparks he proves by experiment and by microscopical observation; and if we regard his supposition of the combustible sulphureous body in steel as merely another mode of describing the combustible nature of the metal, his explanation is perfectly correct, and in accordance with the results of modern chemical discovery: the oxygen in the air "preys upon" the metal, when heated by the percussion which separates it from the mass, converts it into an oxide, which the heat is also often sufficiently intense to vitrify.

In book iii. chap. xxi. of the Pseudodoxia, editions 1672 and 1686, we find the following recurrence to the collision of flint and steel, introduced in the discussion of another subject: "As first, how fire is stricken out of flints? That is, not by kindling the air from the collision of two hard bodies; for then diamonds should do the like better than flints; but rather from sulphureous, inflamed, and even vitrified effluviums and particles, as hath been observed of late."-(1672, p. 176; 1686, p. 124). Upon comparing these two passages from the editions of 1672 and 1686 with the corresponding passages in earlier editions, we find the following differences with respect to the point now before us. Book ii. chap. i.: the words, or vitrified sparks," do not occur in the earlier editions. Book iii. chap. xxi. instead of the words, "but rather from sulphureous, &c.," as above, to the end of the extract, in the editions of 1672 and 1686, we have in the earlier editions only these: "but rather from the sulphur and inflammable effluviums contained in them."

It is clear, therefore, that the Micrographia of Hooke having appeared in the interval between the publication of the first and that of the sixth edition of the Pseudodoxia, our author had perused the work of his great contemporary, and interwoven the results of his experimental investigation of the phenomena of the collision of steel with hard bodies with his own previous hypothetical explanation of themadding, in the first notice of the subject, to the expression, subiect mable effluencies," that of "or vitrified sparks," and also introducing the words, "vitrified" and "particles," into the second.

"inflam

Browne is in error, however, with respect to diamonds, heliotropes, and agates; all which, if their shape be adapted to the purpose, will readily strike fire with steel, and also with each other. If by "marble" he means, as is most probable, the more beautiful rocks and mineral substances employed in building and ornamental architecture in general, he is further in error; for most of these will also strike fire; but few of the substances, however, to which the term marble is now usually applied, possess that property.-Br.

steel, much less with one another. Nor a flint so readily with a steel if they both be very wet, for then the sparks are sometimes quenched in their eruption.

It containeth also a salt, and that in some plenty, which may occasion its fragility, as is also observable in coral. This is separable by the art of chemistry, unto the operations whereof, as calcination, reverberation, sublimation, distillation, it is liable, with other concrations. And in the preparation of crystal Paracelsus * hath made a rule for that of gems. Briefly, it consisteth of parts so far from an icy dissolution, that powerful menstruums are made for its emollition, whereby it may receive the tincture of minerals, and so resemble gems (as Boetius hath declared in the distillation of urine, spirits of wine, and turpentine); and is not only triturable, and reducible into powder by contrition, but will subsist in a violent fire, and endure a vitrification. Whereby are testified its earthy and fixed parts: for vitrification is the last work of fire, e. 6 and fusion of the salt and earth, which are the fixed elements of the composition, wherein the fusible salt draws the earth and infusible part into one continuum; and, therefore, ashes will not run from whence the salt is drawn, as bone ashes prepared for the test of metals. Common fusion in metals is also made by a violent heat, acting upon the volatile and fixed, the dry and humid parts of those bodies; which, notwithstanding, are so united, that, upon attenuation from heat, the humid parts will not fly away, but draw the fixed ones into fluor with them. Ordinary liquation, in wax and oily bodies, is made by a gentler heat, where the oil and salt, the fixed and fluid principles, will not easily separate. All which, whether by vitrification,

a

fusion, or liquation, being forced into fluent consistencies, do naturally regress into their former solidities. Whereas, the melting of ice is a simple resolution, or return from solid to fluid parts, wherein it naturally resteth.

As for colour, although crystal, in its pellucid body, seems to have none at all, yet in its reduction into powder, it hath a vail and shadow of blue; and in its coarser pieces is of a sadder hue than the powder of Venice glass; and this complexion it will maintain, although it long endure the fire. Which, notwithstanding, needs not move us unto wonder; for vitrified and pellucid bodies are of a clearer complexion in their continuities than in their powders and atomical divisions. So stibium, or glass of antimony, appears somewhat red in glass, but in its powder yellow; so painted glass of a sanguine red will not ascend in powder above a murrey.8

As for the figure of crystal (which is very strange, and forced Pliny to despair of resolution), it is for the most part hexagonal, or six-cornered; being built upon a confused matter, from whence, as it were from a root, angular figures arise, even as in the amethyst and basaltes. Which regular figuration hath made some opinion, it hath not its determination from circumscription, or as conforming unto contiguities, but rather from a seminal root, and formative principle of its own, even as we observe in several other concre

7 Venice glass.] A glass made at Venice, of a pebble called cuogolo, resembling white marble, found in the bed of the Tesino.

8 murrey.] Dark, purplish, red: used in this sense by Bacon and Boyle.

9 formative principle of its own.] With respect to rock-crystal, and also gallstones and other substances, as he observes, this is perfectly true: their crystalline forms are not impressed upon them by the surrounding bodies, but are the result of "a formative principle," the peculiar molecular attraction which is inherent in each substance. But all the bodies he subsequently mentions in this paragraph, as far as the cornu ammonis inclusive, although their forms also have undoubtedly arisen from formative principles of their own, do not owe their forms to crystalline attraction, but to organization; for they are all either parts of animals in a fossil state, or natural casts from them; which Browne, with the error common to his age, evidently supposes to be strictly mineral bodies, and not derived from animals; although, as is very remarkable, he actually, in his note to this passage, compares one of these fossils with a recent marine body belonging to the same natural group, the echinide. - See ch. v. of this book, sec. 10. In this steel, much less with one another. Nor a flint so readily with a steel if they both be very wet, for then the sparks are sometimes quenched in their eruption.

It containeth also a salt, and that in some plenty, which may occasion its fragility, as is also observable in coral. This is separable by the art of chemistry, unto the operations whereof, as calcination, reverberation, sublimation, distillation, it is liable, with other concrations. And in the preparation of crystal Paracelsus * hath made a rule for that of gems. Briefly, it consisteth of parts so far from an icy dissolution, that powerful menstruums are made for its emollition, whereby it may receive the tincture of minerals, and so resemble gems (as Boetius hath declared in the distillation of urine, spirits of wine, and turpentine); and is not only triturable, and reducible into powder by contrition, but will subsist in a violent fire, and endure a vitrification. Whereby are testified its earthy and fixed parts: for vitrification is the last work of fire, 6 and fusion of the salt and earth, which are the fixed elements of the composition, wherein the fusible salt draws the earth and infusible part into one continuum; and, therefore, ashes will not run from whence the salt is drawn, as bone ashes prepared for the test of metals. Common fusion in metals is also made by a violent heat, acting upon the volatile and fixed, the dry and humid parts of those bodies; which, notwithstanding, are so united, that, upon attenuation from heat, the humid parts will not fly away, but draw the fixed ones into fluor with them. Ordinary liquation, in wax and oily bodies, is made by a gentler heat, where the oil and salt, the fixed and fluid principles, will not easily separate. All which, whether by vitrification,

a

fusion, or liquation, being forced into fluent consistencies, do naturally regress into their former solidities. Whereas, the melting of ice is a simple resolution, or return from solid to fluid parts, wherein it naturally resteth.

As for colour, although crystal, in its pellucid body, seems to have none at all, yet in its reduction into powder, it hath a vail and shadow of blue; and in its coarser pieces is of a sadder hue than the powder of Venice glass; and this complexion it will maintain, although it long endure the fire. Which, notwithstanding, needs not move us unto wonder; for vitrified and pellucid bodies are of a clearer complexion in their continuities than in their powders and atomical divisions. So stibium, or glass of antimony, appears somewhat red in glass, but in its powder yellow; so painted glass of a sanguine red will not ascend in powder above a murrey.8

As for the figure of crystal (which is very strange, and forced Pliny to despair of resolution), it is for the most part hexagonal, or six-cornered; being built upon a confused matter, from whence, as it were from a root, angular figures arise, even as in the amethyst and basaltes. Which regular figuration hath made some opinion, it hath not its determination from circumscription, or as conforming unto contiguities, but rather from a seminal root, and formative principle of its own, even as we observe in several other concre