although their ingredients be earthy, as glass,3 whose materials are fine sand, and the ashes of kali or fern; and SO will salt run with fire, although it be concreted by heat. And this way may be effected a liquation in crystal, but not without some difficulty, that is, calcination or reducing it by art into a subtle powder, by which way and a vitreous commixture, glasses are sometime made hereof, and it becomes the chiefest ground for artificial and factitious gems. But the same way of solution is common also unto many stones; and not only beryls and cornelians, but flints and pebbles are subject unto fusion, and will run like glass in fire.

But ice will dissolve in any way of heat, for it will dissolve with fire, it will colliquate in water, or warm oil, nor doth it only submit unto an actual heat, but not endure the potential calidity of many waters. For it will presently dissolve in cold aqua fortis, spirit of vitriol, salt or tartar, nor will it long continue its fixation in spirits of wine, as may be observed in ice injected therein.

Again, the concretion of ice will not endure a dry attrition without liquation; for if it be rubbed long with a cloth, it melteth. But crystal will calefy unto electricity, temperature than that at which it boils under the common pressure of the atmosphere; and thus can be made to melt lead, which is quite infusible in common boiling water.—Br.

3 glass.] In the Manchester Memoirs, vol. 2. p. 95, there are some interesting "Remarks on the Knowledge of the Ancients respecting Glass," by Dr. Falconer.

the concretion of ice will not endure a dry attrition, &c.] A similar exertion of ingenuity to that which has discovered a knowledge of the true chemical mixture of the atmosphere in certain mythological tales of the Egyptian priests, and of that of the constituents of water in some of the speculations of Lucretius, might, with far less aberration from the truth, affirm that in this sentence of our author is virtually an anticipation of Sir H. Davy's experiment, in which ice was melted by the mere friction of two pieces of it together. For as a cloth would be a very bad conductor of heat, the experiment of our author might, with care, be so made as to cause the fusion of the ice by the heat generated by the friction alone, independent of that which might (without care) be conducted from the hand of the experimenter through the cloth, and of that also which would be derived from the cloth itself, if not previously reduced to the freezing temperature. It is plain, also, from the author's use of the word "calefy" in the next period, that he believed the ice to be melted by the heat generated by the friction, and not by the friction alone, mechanically considered.-Br.

5 But crystal will calefy unto electricity.] It is an accurate observa

that is, a power to attract straws or light bodies, and convert the needle freely placed :—which is a declarement of very different parts, wherein we shall not enlarge, as having discoursed concerning such bodies in the chapter of electrics.

They are differenced by supernatation or floating upon water; for crystal will sink in water, as carrying in its own bulk a greater ponderosity than the space in any water it doth оссиру, and will therefore only swim in molten metal and quicksilver. But ice will swim in water7 of what thinness soever; and, though it sink in oil, will float in spirits of wine or aqua vitæ. And therefore it may swim in water, not only as being water itself, and in its proper place, but perhaps as weighing somewhat less than the water it possesseth. And therefore, as it will not sink unto the bottom, so neither will it float above, like lighter bodies, but, being near in weight, lie superficially or almost horizontally

tion that rock-crystal becomes electric by friction; but our author is mistaken in attributing the excitation of electricity to the heat produced by the friction. In this case, and in all others of electricity so excited, the agency of the friction appears to be merely mechanical. -Br.

6 They are differenced, &c.] They ; i. e. ice and crystal. Here again we have Ross's ingenious reply; it's no wonder to see a stone sink and ice swim; for crystal when it was ice, swimmed, being now a stone sinks; as being a body more compact, hard, solid, and ponderous; so a stick will swim, but when it is converted to a stone, it sinks. The argument therefore is good thus; crystal sinks, ice swims; therefore crystal is not ice; but it will not follow, therefore, crystal was not ice.” -Arcana, p. 189.

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7 But ice will swim in water.] The whole of this paragraph is excellent, in assertion as well as in argument, giving a very accurate view of the facts described. It is quite true that the ice weighs what less than the water it possesseth," specifically; that is, a bulk of ice equal to that of the water in its liquid form would weigh less than the water; and that this is the reason why it swims upon water. It is also true that ordinary ice is less compact, less continuous in its solidity than other crystalline bodies, and that it is full of spumes and bubbles, and "which abate its gravity." The last statement, that the freezing of water is at the same time condensation and rarefaction, is also correct: that its solid state must imply a kind of condensation, some sort of molecular approximation, is clear; and yet it expands in freezing, and thus unquestionably undergoes rarefaction.Br.

8 somewhat less.] "No more."-Ed. 1646. The specific gravity of ice is to that of water, as 8 to 9. Its greater lightness was discovered by Galileo.

unto it. And therefore also, an ice or congelation of salt or sugar, although it descend not unto the bottom, yet will it abate, and decline below the surface in thin water, but very sensibly in spirits of wine. For ice, although it seemeth as transparent and compact as crystal, yet is it short in either;9 for its atoms are not concreted into continuity, which doth diminish its translucency; it is also full of spumes and bubbles, which may abate its gravity. And therefore, waters frozen in pans and open glasses, after their dissolution, do commonly leave a froth and spume upon them, which are caused by the airy parts diffused in the congelable mixture, which, uniting themselves, and finding no passage at the surface, do elevate the mass, and make the liquor take up a greater place than before: as may be observed in glasses filled with water, which, being frozen will seem to swell above the brim. So that if, in this condensation, any one affirmeth there is also some rarefaction, experience may assert it.1

They are distinguished, in substance of parts, and the accidents thereof: 2 that is, in colour and figure: for ice is a similary body, and homogeneous concretion, whose material is properly water, and but accidentally exceeding the simplicity of that element. But the body of crystal is mixed, its ingredients many, and sensibly containeth those principles into which mixed bodies are reduced. For beside the spirit and mercurial principle, it containeth a sulphur or inflam

9 yet is it short in either.] "Yet is it inferior to crystal, both in transparency and compactness."

1 which are, &c.] From 1. 11 to the end of the paragraph was added in 2nd Edit.

2 They are distinguished, &c.] Ross again meets the author on the hypothesis, that no present difference between ice and crystal can prove that the one may never have been the other. "Crystal is not so much distinguished either in substance or accidents from ice, as a chick is from an egg, and yet the chick was an egg."-Arcana, 190.

3 For besides the spirit and mercurial principle, &c.] Our author's notions of the chemical nature of rock-crystal are those of the alchemists, and are wholly unfounded. There is neither spirit, mercury, nor sulphur, in rock-crystal; at least, nothing to which those appellations can properly be applied: it is silica, or the earth of flints, in a pure crystallized form, itself composed of equal weights of silicon (a single combustible substance), and oxygen. It may be suspected, with some plausibility, however, that the notion of the alchemists, that

mable part, and that in no small quantity; for, besides its electric attraction, which is made by a sulphureous effluvium, it will strike fire upon percussion, like many other stones, and, upon collision with steel, actively send forth its sparks, not much inferiorly unto a flint. Now such bodies as strike fire, as have sulphureous or ignitable parts within

such bodies as rock-crystal and the precious stones contained sulphur, might have arisen from their having, in some of their multifarious operations, actually separated its combustible base; they always attributing combustibility to the presence of sulphur. Although they were altogether ignorant of the true nature of the processes which they em ployed, and of the effects which they witnessed, it cannot be doubted, that in their operations many of the simple as well as compound bodies, which modern chemists have described, would occasionally be evolved, though, in most instances, they would be caused again to enter into combination immediately, or be confounded with other well-known bodies, and, in either case, they would of course escape detection and record.-Br.

4 Now such bodies strike fire, as have, &c.] The scientific reader might at first infer, from the perusal of this passage, that, as the Pseudodoria was first published in 1646, our author had anticipated the celebrated Hooke in his experimental investigation of the nature of the sparks produced by the collision of flint and steel. A comparison, however, of the passage as it stands in the edition of 1672 (the last revised by the author), with the corresponding one in all the previous editions, and a reference to a further allusion to the subject in book iii. will show that Browne's statements on the subject were corrected and matured subsequently to the promulgation of Hooke's results, and that all his definite knowledge respecting it was borrowed from the latter, as, indeed, he has fairly, though indirectly, acknowledged. As the present annotator at first made the above inference himself, and (the subject being of some importance in the history of science) was induced to examine the seeming anticipation somewhat minutely, it may be as well to introduce here the entire examination; this, while it proves that Browne's knowledge on the point was derived from Hooke, as just stated, will evince also the diligence with which he investigated, and the candour with which he adopted the discoveries of his contemporaries.

It will first be proper to cite the statement of Dr. Hooke.-He informs us in his Micrographia (published in 1665), p. 44-46, that, about eight years before, he came, from experiment, to the following conclusions: that a spark struck from a flint and steel was nothing else but a small piece of the steel or flint, but most commonly of the steel. which, by the violence of the stroke, is at the same time severed and heated red-hot, and that sometimes to such a degree, as to make it melt into a small globule of steel, and sometimes further to vitrify it; phenomena which he ascribes to the existence in iron or steel of a very combustible sulphureous body "which the air very readily preys upon

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, "inflammable effluencies," that of "or vitrified sparks," and also introducing the words, "vitrified" and "particles," into the second.

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.