John Rey

John Rey (1583–1645) (or, in French) Jean Rey, was a physician of Périgord, France who in 1630 published a tract on calcination, or oxidation of metals, after being notified by Brun, an apothecary of Bergerac, France, of Brun's experiments (as early as 1629) on the calcination of tin. Brun had melted 2 pounds six ounces of tin, and after 6 hours the resulting calx weighed seven ounces more than the original tin. More than one hundred and forty years before Antoine Lavoisier, John Rey recognized that in the calcination of lead or tin, part of the air provided an increase in mass to the calcined metal oxide. His work was eclipsed first by the phlogiston theory and then later, by Lavoisier's discoveries disproving the existence of phlogiston. Lavoisier's oxygen theory confirmed Rey's earlier report, of which Lavoisier claimed he was unaware. After the presentation of Lavoisier's 1775 memoir at the Académie des sciences, Pierre Bayen (1725-1798) wrote a letter to Abbé François Rozier, director of the journal Observations sur la Physique, sur l'Histoire naturelle and sur les Arts, to ask him to publish an update notice, recognizing the priority Rey's work.

Quotes

Art IX. A Translation of Rey's Essays on the Calcination of Metals, &c. (1821)

The Quarterly Journal of Science, Literature, and the Arts, Vol. XI (1821) pp. 80-83. A translation as communicated by John George Children, Esq., F.R.S., &c. Ref: Rey J., Essays de Jean Rey, sur la recherche de la cause pour laquelle l'estain et le plomb augmentent de poids quand on les calcine. Nouvelle édition revue sur l'exemplaire original et augmentée sur les manuscrits de la Bibliothèque du Roi et des Minimes, avec des notes par M. Gobet. Paris, Ruault, 1777.

Essay I. All matter under the compass of the Heavens, has weight.

God, creating the universe, neither made it perfectly like Himself, nor perfectly unlike, for He, being One, has made the world as not one, from the diverse multiplicity of its innumerable parts, ordaining, nevertheless, that they should collect into a certain unity by their exact contiguity. The upper world has no connexion with this subject; the lower, and elementary world, owes this contiguity to the weight divinely impressed on its parts, aided by the subtle fluidity of some of its simple bodies. It is by this quality, with which the matter of the four elements is more or less invested, that they are separated from one another, and each transported to its proper place, as the generation of compounds, and the beauty of the universe requires.

For this matter, every where filling the space closed in by the curvature of heaven, is continually pushed, by its own weight, towards the centre of the world. Earth, it is true, as the heaviest, readily occupies this situation, and forcing its fellow-elements to retire, causes water, the second in weight, to be also second in place; so that the air, driven from the lowest, as well as the second station, holds the third place, leaving the highest region to be occupied by fire, the lightest of all.

The chemists furnish us with a pretty representation of this, by taking pulverized black enamel, liquor of tartar, brandy tinged blue with litmus, and spirit of turpentine reddened by alkanet, and shaking the whole together in a phial, till it forms one confused mixture. The vessel being then left at rest, it is pleasant to see the clearing off of the confusion. The enamel gains the lowest station, representing earth; the liquor of tartar settles close by it, representing water; the brandy, like the air, occupies the third place; and spirit of turpentine, to shew the nature of fire, arranges itself above them all. All this is effected by the influence of weight, according as it is largely or sparingly distributed amongst these bodies. In the same manner the elements acknowledge no other cause that arranges and disposes each in its proper place, it being needless to introduce levity, which our predecessors vainly devised for that purpose.

Essay II. There is nothing absolutely light in Nature.

Almost all philosophers, ancient and modern, fearing an eternal confusion of the elements, were they all endowed with weight, conceived the two uppermost to be furnished with a certain levity, by means of which they bounded up on high, each to occupy its peculiar place, like as the two lower ones are pushed downwards by their own weight. But having clearly shewn in the last Essay, that levity is not necessary for that effect, weight alone being sufficient, I embrace the maxim, which they themselves have prudently laid down, that we should never multiply existences unnecessarily; assuming that God and Nature do nothing in vain, (which they also teach.) I think it would be otherwise were we to admit levity, since it is of no use.

I say much more; that fire, being of so subtile a nature, that it can hardly be called a body, is consequently almost stripped of all resistance; whence it follows, that the air, mounting up without impediment, would reach the skies, driving fire from its place, and compelling it to seek a lower station, to the injury of their own doctrine. To this I will add another inconvenience, namely, the perpetual and unprofitable strife, which would ensue between the heavy and the light elements, the latter pulling upwards, and the former downwards, with all their might; whence would arise, at the place of their contiguity, incomparably greater distress than the packthread experiences which is pulled in opposite directions by two strong hands, till at last it is broken by their efforts: far different from that knot of friendship, in which nature has been pleased to unite the neighbouring elements, planting in their bosoms similar qualities, whence they communicate and amicably sympathize with each other. It follows from all this, that levity is a term that signifies nothing absolute in nature, and must be rejected; or, if we retain it, it must only be to denote the relation of one substance having less weight to another which has more.

Essay III. There is no natural Motion in the upper Regions.

What shadows would be if there were no bodies, such natural motion in the upper regions will become, without levity. For, of a truth, it would be monstrous, to see natural effects without a natural cause. That is said to move naturally whose cause of motion is in itself.

Now casting a look on all that moves, I see nothing that ascends by its own proper motion. Water, indeed, rises in a glass, if we throw earth into it; but all will allow, that it is not from any levity that is in the water, but rather, that the earth, by falling to the bottom, makes the water ascend. Now, if water does not acknowledge levity as the cause of this motion upwards, why should air confess it, which ascends in like manner when pressed on by water? Why fire, which does the same? It will be said, I doubt not, that if the upward motion of the elements be not natural to them, it must be violent; whence this absurdity follows, that each obtains its place in the universe by force. To this I answer, that the elements not having the cause of these motions in themselves, they may, so far, be called violent; but that this violence is gentle, and nowise ruinous.

Thus, the motion of the orbits of the planets from east to west, having its cause in a higher heaven, is called by all violent, without, however, its doing them any injury. Moreover, they who argue thus condemn themselves, since they are compelled to admit, that not only the motion of water and air, but their very abiding places, are held by violence:—that of the latter, under fire, and that of the former, above earth.

Having thus vanished levity, and its upward motion, from all the boundaries of nature, we aver anew, that the elements of air and fire, which alone come into the dispute, are endowed with gravity.

Art. XI. A Translation of Rey's Essays on the Calcination of Metals, &c. (1822)

The Quarterly Journal of Science, Literature, and the Arts, Vol. XII (1822) pp. 294-299. A translation as communicated by John Goerge Children, Esq., F.R.S., &c. Ref: Rey J., Essays de Jean Rey, sur la recherche de la cause pour laquelle l'estain et le plomb augmentent de poids quand on les calcine. Nouvelle édition revue sur l'exemplaire original et augmentée sur les manuscrits de la Bibliothèque du Roi et des Minimes, avec des notes par M. Gobet. Paris, Ruault, 1777.

Essay XV. Air dimishes in weight in three ways. The balance is deceitful, the means of remedying that.

[N]othing gains weight but by the addition of matter, nor loses it but by its subtraction—so inseparably are matter and weight united, as has been shewn above in the sixth essay.

But if we investigate the subject by the balance, a case occurs in which, without any addition or subtraction of matter, a substance will appear more or less heavy; namely, by its contraction or expansion.

Hammer a piece of cold iron for a considerable time; you will unite its parts and diminish its bulk, and then it will appear heavier when put into the balance.

[T]wo ingots one... of gold, and the other of iron, which appear by the balance to be equal, are nevertheless not so—for the iron is as much heavier than the gold, according to reason, as the air which it displaces is heavier than that displaced by the gold...

Essay XVI. Formal answer to the question, Why Tin and Lead increase in weight when they are calcined?

I have now made the preparation; laid as it were the foundations of my answer to the Sieur Burn's [or Brun's] demand; namely, that having put two pounds six ounces of fine English tin into an iron vessel, and heated it strongly on an open fire for six hours, stirring it continually, without having added anything, he obtained two pounds thirteen ounces of a white calx; which at first occasioned him great surprise, and the desire to ascertain whence these seven ounces of increase were derived.

[W]e must not only inquire whence these seven ounces are derived, but, moreover, whence that which has replaced the loss of weight, necessarily arising from the enlargement of volume of the tin, by its conversion into calx, and from the vapours and exhalations that have escaped.

I answer, and proudly maintain, "That this increase of weight comes from the air, thickened and made heavy, and in some measure rendered adhesive in the vessel by the violent and long—continued heat of the furnace—which air mixes with the calx (its union being assisted by the continual stirring), and attaches itself to its smallest particles—no otherwise than as water, when sand is thrown into it, makes it heavier by moistening it, and adhering to its smallest grains."

I imagine there are many persons who would have been startled (effarouchées) at the mere statement of this answer, had I given it in the outset, that will now receive it willingly, being, as I may say, tamed (apprivoisées) and rendered tractable, by the evident truth of the preceding essays. For doubtless they whose minds were preoccupied with the opinion that air is absolutely light, would have rushed to the encounter, exclaiming, Why do we not extract heat from cold, white from black, light from darkness, if from air, a thing absolutely light, we can extract so much weight? And they, who might have given credit to the weight of air, would have been unable to persuade themselves, that it could ever increase the weight of a substance balanced in itself.

On this account I have been obliged to shew, that air is possessed of weight; that it is proved by other investigation than that of the balance; and that even by that instrument, a portion previously altered and thickened, may make its weight manifest.

Essay XVII. It is not the disappearance of the celestial heat which animates the Lead,

or the death of that latter that increases its weight in calcination.

Cardan is the first, who in his fifth book, De Subtilitate, says, that lead, by conversion into ceruse, or by calcination, gains one-thirteenth part in weight, and gives this reason for it—The lead dies, for the celestial heart, which was its soul, vanishes; whose presence gives it life, and renders it light; as its absence occasions its death, and makes it heavy.

This he confirms by the example of animals, which become heavier after death, from the extinction of the celestial heat, the soul, (as he thinks), both of animals and all other mixed and compound bodies.

This opinion is defective, to say no worse of it, in many respects. First, in attributing life to lead. Secondly, in supposing that the presence of the celestial heat makes it light, and its absence heavy. Thirdly, because it assigns the same reason for the increased weight of lead by calcination, and of animals by death. There is nothing of the kind. For as to life, how can lead possess it, since it is a homogeneous body, without difference of parts, without organs, and without any vital effect or action? If it move downwards, so does ceruse, which is only its corpse; if it be cooling (rafraischit), so is ceruse. Then how could it preserve this life, under a million of forms, that it may be made to assume and to cast off, yet always continuing to be lead? How, in the furnace (which would be a much greater wonder), where it may be kept in fusion a day, a month, or a whole year? It must have a very tenacious soul to undergo so much without being dislodged!

Moreover, all the world is agreed, that from death to life there is no return. Yet the chemists assure us, if we moisten the calx of lead, and mix it with water in which samphire (salicot) has been dissolved, then, having dried it, put it in a crucible with a small vent, and heat strongly and quickly, that we shall reduce it to its original state.

With regard to the celestial heat making bodies light, Scaliger very properly objects that the heavens, which abound in this heat, as being the source of it, must be light (feut leger) and consequently univocal (univoque) with the other bodies, which is absurd.

Neither can the loss of this heat render them heavy, for I have already proved that nothing increases in weight but by the addition of matter, or by diminution of volume; but here there is nothing of the kind; so that the disappearance of the heat cannot add any thing, and as to its bulk, it is visibly enlarged; the compact and solid substance of the lead being reduced (amenuisée) to so many small parcels, that their number is almost infinite.

Plants too ought to become heavy by death, the celestial heat being expelled: but the contrary is evident to all. As to the increased weight of animals by death, the true cause, far remote from that which increases the weight of lead when calcined, is this: in the living animal its natural heat subtilizes, dilates, and augments the dimensions of the humours, the flesh, and every thing in it capable of dilatation—but losing this heat by death, the whole on this becoming cold, contracts and diminishes, whence the increase of weight, as I have often said already. What is there like this in lead?

Thus the opinion of Cardan appears so frivolous, that I am grieved that a great man, and one who is justly esteemed by all the world, should have lately declared to me that he inclines towards it.

Quotes about John Rey

Sir, I did not know about the book of John Rey until after I published through your Journal, the second part of my experiments on mercurial lime. So I could not talk about it in the very brief enumeration that I then made of the different opinions on the cause of the increase in gravity of metallic lime. My fault, however involuntary it may have been, must be repaired and, in order to do so, I hasten to do justice to an Author who, by the depth of his speculations, has succeeded in pointing out the real cause of this increase. Might you, Sir, work with me to make known the excellent work of Jean Rey? Your Journal is read throughout France and is recognized in foreign countries. If you wanted to insert the attached leaflet into it, chemists in all countries would know in a short time that it was a Frenchman who, by the force of his genius and his reflections, was the first to guess the cause of the increase in weight which certain metals undergo when, on exposing them to the action of fire, they are converted into lime, and that this cause is precisely the same as that the truth of which has just been demonstrated by the experiments which M. Lavoisier has read at the last public meeting of the Academy of Sciences.
- Pierre Bayen, Letter to M. L'Abbé Rozier (January, 1775)

It appears from these essays, which are not new productions, but tracts of near a hundred and fifty years standing, that the chemical experiments and discoveries, which have lately made so much noise in England and France, were long since made and exhibited by a provincial physician of Perigord. It is true that the main object of these essays, when first published, was to account for the additional weight of metals by their passing through the fire. The fact was known to Boyle and others, who imputed it to the weight deduced from heat; as Buffon hath done long since, imputing gravity to fire. Dr. Rey, however, so long ago as the year 1630, attributes such additional weight to the condensed, or fixed, air; which attaches itself to the calcined substance, and that in proportion to the division of its parts.—It is farther remarkable, that, in a small tract annexed to these essays, the present Editor gives us an account of a method, used upwards of fifty years ago, to pour fixed air out of one vessel into another; which is the very same made use of by Dr. Priestley, Lavoisier, and other modern experimentalists.—A considerable part of the volume contains the learned correspondence that passed between the author, Dr. Rey, and the celebrated Father Mersenne.
- W. Kenrick, LL.D. and Others, Foreign Catalogue. Essays de Jean Rey, Docteur en Medecine, sur la Recherche de la causa pour laquelle l'Estain et le Plomb augmentent du poids quand on les calcine, &c.—Or Essays, by John Rey, M.D. on the Investigation of the Cause why Lend and Pewter increase in weight by Calcination. 8vo. Paris. London Review of English and Foreign Literature (1767) Vol. VI, pp. 496-497,

One of the Authors who has written the most ancient on this object is an almost forgotten doctor, named John Rey, who lived at the beginning of the 17th century in Bugue en Périgord, and who was in correspondence with the small number of people who cultivated the sciences at that time. Neither Descartes nor Pascal had not yet appeared; we knew neither of Boyle's vacuum nor of this discovery.
- Marie-Anne Paulze Lavoisier, Memoirs of Lavoisier (1805) posthumous publication by Lavoisier's wife.

Ignorance of the history of science is the cause why we frequently look back with a kind of contempt also on the second period of chemistry, namely, the phlogistic period, and regard it as insignificant. Our self-esteem deems it inconceivable that the experiments of John Rey, on the increase of weight in metals during the operation called calcination, remained unregarded; and that, while these experiments existed, the idea of phlogiston could be developed and obtain a footing. But all the efforts of that age were directed to the arrangement of that which was ascertained, and which waited only for arrangement. Rey's observations had no influence whatever on that period, because they were not yet brought into connection with the process of combustion generally; for there were many bodies which, by combustion, became lighter, or disappeared to the senses. The object of the labours of Becker and Stahl and their followers was the discovery of these phenomena which belonged to the same class and were produced by the same cause.
- Justus Freiherr von Liebig, Familiar Letters on Chemistry: In Its Relations to Physiology, Dietetics, Agriculture, Commerce, and Political Economy (1859) p. 57.

In the year 1629, Brun, an apothecary residing in the town of Bergerac, in France, melted two pounds six ounces of tin, and in six hours, the whole was converted into a calx, which weighed seven ounces more than the tin employed. Brun astonished at this circumstance, (for it was not then known that metals experienced an encrease of weight during their calcination,) communicated it to John Rey, a physician of Perigord, who, in 1630, published a tract upon the subject, in which he justly refers the encrease of weight to the absorption of air. "Thus," says Rey, in the fanciful language of the period, "have I succeeded in liberating this surprising truth from the dark dungeons of obscurity; which was vainly, but laboriously, sought after by Cardan, Scaliger, [Augustus Henricus] Faschius [or Augustin Heinrich Fasch], Cœsalpinus, and Libavius. Others may search for it, but in vain, unless they pursue the royal road which I have cleared. The labour has been mine—the profit is the reader's—the glory is from above!"
- Sholto & Reuben Percy, The Percy Anecdotes (1823) Vol. VI. Science and Literature, "Calcination" p. 65.

Art. IX. A Translation of REY’s Essays on the Calcination of Metals, &c. (1821)

John George Children, Esq., F.R.S., &c. The Quarterly Journal of Science, Literature, and the Arts, Vol. XI (1821) pp. 72-79.

Introduction

The original edition of Rey's Essays, of which there is a copy in the library of the British Museum, was published at Bazas, a town about thirty miles S.E. of Bourdeaux, in the year 1630. In 1777, it was reprinted with notes, by M. Gobet, at Paris, and published by Ruault, Rue-de-la-Harpe. The copies of this reprint disappeared in a very sudden and remarkable manner, and the work was so little known in this country, that Doctor James Curry, at the sale of whose library, in 1820, I purchased a copy of it, states in a note at the beginning of the work, apparently in his own hand-writing, that he had sought it, in vain, for more than ten years, in every bookseller's catalogue in London, till, at last, the present copy rewarded his trouble, and he adds, that he had seen but one other copy since. The suppression of this edition, almost immediately after its publication, which took place in about three years from the promulgation of Lavoisier's first experiments would naturally lead to the suspicion, that it was effected by that celebrated philosopher or his friends, to avoid the imputation of plagiarism, which might sully the brilliancy of his recent discoveries, and this imputation is, in the opinion of many, but too probable.

Mr. Brande, however, has given an interesting note in his Dissertation on the Progress of Chemical Philosophy, prefixed to the third volume of the Supplement to the 4th and 5th editions of the Encyclopædia Britannica, containing a quotation from two scarce volumes of the posthumous works of Lavoisier, in Mr. Hatchett's library, in which Lavoisier expressly states, that he knew nothing of Rey's Essays, when, in 1772, he undertook a series of experiments on the different kinds of air or gas, disengaged during effervescence, and in many chemical operations; whence he learnt the true cause of the increase of weight, which metals acquire by the action of fire. At the end of that note, he further states a precaution he had taken in November, 1772, to secure to himself the sole merit of the new French theory, claiming it exclusively for his own.

It would be uncourteous, were that celebrated philosopher still living, and ungenerous now he is dead, to question the truth of his assertion; nor do I conceive I have any more right than I have inclination, to do so. His ignorance of Rey's work is, perhaps, not very extraordinary, since, as will appear by M. Bayeu's letter, at the end of the Avertissement, that the book was extremely rare, and probably known to very few. After the publication of that letter, however, in 1775, Lavoisier must have known, and have read Rey's Essays, as, indeed, appears from his own words in the note already quoted; and, it is matter of regret, that he never did that extraordinary man the justice of mentioning his name, either in his papers read before the Academy of Sciences, or in his Elements of Chemistry, published in 1789. This, probably, proceeded from his considering Rey's opinions as mere speculations (see the preceding note); the reader will judge, whether they deserved no higher, praise. How ready Lavoisier was to do justice to his cotemporaries, may be gathered from his conduct towards Doctor Priestley, respecting the discovery of oxygen gas; and it will hardly be considered an uncharitable inference, if we suspect something of the same spirit to have influenced, him with regard to Jean Rey.

The following translation is from the copy of 1630. I have endeavoured to keep as close to the style of the original as I could, and perhaps the reader may sometimes think I had better have been less curious in my attempts to imitate its quaintness. He will too, occasionally, find the matter redundant, and the argument tedious. I once proposed to abridge it, but better judgments preferred giving it in its entire form, as a work, when divested of the rude philosophy of the day, of unquestionable genius and singular penetration, and one which, if not itself the real basis of modern chemistry, contains at least, such principles, that, had they, been duly appreciated and followed up from the instant of their promulgation, could hardly have failed, long since, to have raised the science to an equal, or, perhaps, even a greater, height than that which it at present holds.

The re-print contains an Avertissement, parts of which I have thought worth inserting, as well as a letter of M. Bayen to the Abbé Rozier.—The first gives a short account of Rey, and mentions some facts which shew his work to have been well known and highly esteemed by Professor [Jakob Reinbold] Spielman of Strasbourg, as late as the year 1766, and to have been honourably spoken of by M. de Bordeu, circumstances which make Lavoisier's ignorance of its existence still more extraordinary.

A Letter from M. Bayen,

chief Apothecary of the Army, &c., to M. L'Abbé Rozier, Dignitary of the Church of Lyons, &c. Letter to M. L'Abbé Rozier (January 1775)

The cause of the increased weight that certain metals experience by calcination, has, at all times, been a subject of speculation and research with chemists and natural philosophers. Cardan, Cæsalpin, Libavius, and many others, formerly endeavoured to explain this phænomenon; but amongst them all, we must, in justice, distinguish John Rey, a physician of Perigord, who lived at the beginning of the last century. His work, perhaps unknown to all the chemists and naturalists of the present day, appears the more deserving to be rescued from oblivion, because the reason which he assigns for the increased weight of the calces of lead and tin, has an immediate relation with that, which is on the point of being acknowledged by all chemists.

It was not, Monsieur, till after I had published in your journal, the second part of my experiments on the calces of mercury, that I became acquainted with Rey's book. I could not mention it in the very short enumeration I then gave of the different opinions on the cause of the increased weight of metallic calces; my fault, involuntary as it was, must be repaired, and to this end, I hasten to do justice to an author, who, by the profoundness of his speculations, has succeeded in assigning the true cause of that increase.

I hope, Monsieur, that you will concur with me, in making known Rey's excellent work. Your journal is read throughout France, it is spread over foreign countries; if you would insert this notice in it, the chemists of all countries would soon know, that it was a Frenchman, who by the power of his genius and reflections, first guessed the cause of the increased weight that certain metals experience when converted into calces, by exposure to the action of fire, and that it is precisely the same as that, whose truth has just been proved by the experiments which M. Lavoisier read at the last public sitting of the academy of sciences.

P.S. We may presume, that copies of Rey's work are rare. That which I have before me belongs to M. de Villiers, physician of the faculty of Paris, who has the best chemical library in France, and which he has sincere pleasure in laying open to the cultivators of the science. M. de Villiers's copy came from the library of the late M. Villars, physician at Rochelle, which was sold by his heirs in the course of last year. This copy was defective, it ended at p. 142, containing only the beginning of the 28th Essay. I requested M. Capperonier to allow me to transcribe, from the copy in the king's library, the two pages that are wanting in M. de Villiers's,—which he had the goodness to accede to. Thus, they who may wish to read John Rey's work, are informed, that there is a copy of it in the king's library, at the end of which they will find two manuscript letters; the first from Father Mersene to the physician, John Rey, in which he attacks the natural philosophy of that author,—the second, Rey's answer to Mersene, in which he defends himself with all his might.

M. Brun's Letter, which gave rise to the present Essays.

Sir,—Wishing a few days since, to calcine some tin, I weighed out two pounds six ounces of the finest sort, from England, put it into an iron vessel fitted to an open furnace, and keeping it continually stirred over a strong fire, without adding any thing, I converted it in six hours, into a very white calx. I weighed it to ascertain the loss, and found there were two pounds thirteen ounces of it. This occasioned me incredible astonishment, not being able to imagine, from whence the seven ounces of increase could be derived. I made the same trial with lead, of which I calcined six pounds, but in this I found a loss of six ounces. I have inquired the cause of many learned men, particularly of Dr. N. but no one has been able to declare it.

Your ingenuity which, when it pleases, soars beyond the common flight, when it pleases, will here find matter of occupation, and I beseech you most earnestly to inquire into the cause of so rare an effect, and so far to oblige me that, by your means, I may be enlightened in regard to this miracle.

On the Supposed Nature of Air prior to the Discovery of Oxygen (1864)

"9. John Rey" by George F. Rodwell, F.C.S., The Chemical News and Journal of Physical Science (Oct 29, 1864) pp. 208-210. Also in the Journal of the Franklin Institute, Third Series, Vol. XLIX. Whole No. Vol. LXXIX (Jan-Jun 1865) pp. 336-340, and the London Chemical News, No. 255.

Rey's first object was to prove that the air has weight: taking it for granted that bodies cannot descend unless they possess weight...

The eleventh of Rey's essays... argues... air may be distilled a thickened air being left as residue.

The sixteenth essay... he writes, "...this increase of weight comes from the air thickened and made heavy and in some degree rendered adhesive in the vessel by the violent and long continued heat of the furnace, ..."

In the eight following essays Rey refutes the opinions of Cardanus and Cæsulpinus, and of several friends of Le Brun, who attributed the increase of weight to the absorption of "the vapors of charcoal," of "the volatile salt of charcoal," of "the volatile mercurial salt," of "moisture attracted by the calx," and of matter removed from the calcining vessel.

In the twenty-fifth essay Rey mentions a single experiment which refutes the opinions of all his adversaries. It will be observed that the above objections are founded on the mode of heating the metal to be calcined. Rey now proves that heat and air alone produce the change.

Hamerus Poppius mentions an experiment in which he calcined antimony by converging the rays of the sun upon it by a lens. ...Now, in this instance Rey argues, it is impossible that "the vapors of charcoal," or any of the other volatile bodies supposed to be produced during the calcination in a furnace could have attached themselves to the calx, and yet it was found to weigh more than the antimony which produced it.

Rey, by careful observation, became convinced that the weight gained by metals during calcination came from the air alone. It was then necessary to construct a theory to show by what means air could produce such an effect.

The train of reasoning which induced him to propound the theory... may be stated... Air has weight; air most nearly approaches the nature of a liquid, and may therefore be supposed to act like one; liquids may, by the action of heat, be caused to separate into a heavier and a lighter part; therefore air may, by the action of heat, be caused to separate into a heavier and a lighter part; the heavier part approaches more nearly to the nature of a liquid than air; it is the "dregs" of air, and it has changed its fluidity for a "viscid grossness;" this matter attaches itself to the ashes of bodies during calcination as water attaches itself to sand, and renders such of them as possess much ash heavier than they were before calcination.

Rey did not believe that "thickened air" (l'air espessi) is the cause of calcination. He held to the old theory that calcination is the expulsion by heat of the volatile matter of the body calcined, the calx being the residual ash;—the ash of an organic body was to his mind as much a calx as the oxide of a metal.

The great merit of Rey was, that he regarded air in the light of a ponderable liquid; that which holds good for a liquid, he assumed, holds equally good for air. He thus became able to grapple with an intangible body, and to reason on that which had hitherto from its subtlety eluded the grasp of the philosophers of all previous ages.

Rey's theory was, indeed, fallacious; still, it was a great step in advance of all that had been done in former ages; there is impressed upon it a stamp of a great and energetic intellect. We must not judge of it by what has been done since; we must think of what was done before; we must think of it as the work of a man removed from a great centre of learning; from the converse of scientific men; from every external source of knowledge; compelled to work alone, to think alone. Let it be remembered, moreover, that experimental science had not yet left its cradle; middle age superstition was still very rife; philosophy founded on reasoning had not given way to philosophy founded on experiment; the syllogism had not yielded its place to induction; the Church was still dominant—still condemned all that was contrary to the philosophy of Aristotle, and thus cramped and curbed the human intellect; the "Novum Organum" had but just appeared; and the "Dialoghi" of Galileo were as yet unknown to the world.

Rey lived at the commencement of an epoch, and he was the founder of a branch of scientific inquiry which helped to render that epoch glorious. By energy and perseverence he ascended a lofty eminence, whence he saw in the distance an unknown country—dimly, indeed, and far from him; still it was there, and he pointed out its direction to his fellow-men; but explorers were rare in that day, and men cared not to venture across pathless wastes, to ascend hitherto untrod mountains, in order to arrive at that which, when found, might prove a barren and unproductive country.

Rey's work was but little known during the 147 years which intervened between its publication and its reprint in 1777. It was published in a small and obscure town of Provence, and from the fact that at the time of the reprint it was extremely scarce, it is to be supposed that only a few copies were originally printed. Had it been better known, the theory of Phlogiston would never have been propounded, and pneumatic chemistry would assuredly sooner have attained the rank of a science.

But soon after the "Essays" were published, the discovery of the pressure of the air diverted the minds of the scientific from the study of the chemistry of the air.

The claims of Rey have never been sufficiently acknowledged. Let all honor be given to him; science ought to venerate such a man—a true philosopher, working for her, and loving her for herself alone.

In the history of pneumatic chemistry the name of Rey deserves to stand side by side with those of Mayow, Hales, Priestly, Scheele, and Lavoisier.

Well did Rey write as the concluding words of his treatise: "Le travail esté mien, le profit en soit au lecteur, et à Dieu seul la gloire."
- Translation: The labour has been mine, may the profit be to the reader, and to God alone the glory.