# Popular Science Monthly/Volume 44/December 1893/The Essays of Jean Rey

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* THE ESSAYS OF JEAN REY.
By MM. L. A. HALLOPEAU and ALB. POISSON.
AMONG the men of science of the first half of the seventeenth century the name of Jean Rey, doctor, of Périgord, was long forgotten and is still little known. He was born toward the end of the sixteenth century, at Bugues la Dordogne. Hardly anything is known of his life. He was a doctor of medicine, and devoted himself for several years to researches in chemistry and physics, in co-operation with his elder brother, also named Jean Rey, Sieur de la Perotasse, proprietor of the iron forge at Rochebeaucourt, la Dordogne. He died in 1645, and his days may have been cut short by grief over a disastrous lawsuit.
Jean Rey invented a water thermometer, or thermoscope, and a wind arquebus, and he even thought of applying his thermometer to the uses of medicine. It was certainly one of the first instruments invented to measure differences of temperature. In his description of it he said: "It is nothing but a little round vial with a long, uncorked neck. In using it, I place it in the sun or in the hands of a fever patient, after having filled it, all except the neck, with water. The heat, dilating the water, causes it to rise more or less, according as the heat is great or little."
He wrote one little book of a hundred pages, dedicated to the Count de la Tour d'Auvergne, which was printed in 1630, under the title of Essais de Jean Rey, Doctor of Medicine, on an investigation of the cause of the increase in weight of tin and lead when they are calcined. This work was not understood by the learned men of that period. It was probably not very widely published. ​and only two copies of the edition existed in the middle of the eighteenth century. But one of these copies was complete. It belonged to the great library of the king. It was, however, reprinted in 1777 by Gobet, who also reprinted, about the same time, the works of Bernard Palissy. After the essays, Gobet published a part of Key's correspondence with Père Mersenne relative to them, and there are probably still other letters in the manuscript correspondence of Père Mersenne. Key's book was therefore well published at the close of the eighteenth century. Nevertheless, this edition, too, is now very rare, and only three copies exist in the libraries of France.
As very few persons of this age have read the Essays of Jean Key, we have thought it might be of service and cast some light on the history of science, obscure in its beginnings, to give a brief but exact analysis of its contents. Judging by his writings, Jean Key appears to have had very extended scientific knowledge and a talent for experimentation rare in his time. He was, furthermore, in pleasant relations with most of the learned men of the period, who were accustomed to consult him in difficult cases, while he was correctly informed of all that had been done in France and other countries. Three men in particular were closely associated with his works—viz., the Sieur Brun, master apothecary of Bergerac; Deschamps, a physician of the same city; and Père Mersenne, of the order of the Minims, who had a continuous and interesting correspondence with him.
Key's experiments were undertaken at Brun's request. Brun's letter, giving as it does an idea of the confidence which Key inspired among his contemporaries and of his high reputation, merits publication entire. He wrote: "Desiring a few days ago to calcine some tin, I weighed two pounds and six ounces of the finest English metal, put it in an iron kettle on an open furnace, and, stirring it continually without making any change in the adjustment, I converted it in six hours into a very white earth. I weighed it to determine the loss, and found that it weighed two pounds and thirteen ounces. This astonished me incredibly, for I could not imagine where the surplus seven ounces had come from. I performed the same experiment with lead, and calcined six pounds. I found it had gained six ounces. I asked the cause of this from many learned men, particularly from Dr. N. (Deschamps), but none of them could explain it to me. Your brilliant mind, which soars, when it is so disposed, above the common, will find matter to occupy itself with in this. I implore you with all my affection to employ yourself with the search for the cause of so rare an effect, and to oblige me so much that by your aid I may be enlightened respecting this wonder."
Key immediately set himself to work to find the answer to this ​question—one of "the most difficult that philosophy has ever brought forth." It was not without emotion that he took up the pen: "Believing I have reached the end of the matter, I produce these my essays, not without well foreseeing that I shall be called rash, for in them I shall disturb some of the maxims that have been approved for ages by most philosophers. But what can there be rash in exposing the truth to the light after having found it?" The book of twenty-eight chapters or essays is divided into distinct parts. In the first part the author, as it were, prepares his reader for the ideas he is about to set forth in the second. He first demonstrates the weight of the air—an entirely new fact in science then—and next he applies the ideas he has just enunciated to the explanation of the weight of lead and tin when calcined in the air.
The great physicists of the seventeenth century had as yet produced nothing when Jean Rey's essays appeared. Otto von Guericke was only twenty-one years old; Torricelli was still studying mathematics at Rome, and his celebrated experiment was not performed by Viviani till 1 643. Galileo was the only one who might at that moment have had established ideas on the weight of the air, and his Dialogues on the Motion and the Resistance of Fluids was not published at Leyden till 1638.
Rey was therefore the first person who declared that the air has weight, and he alone has the right to all the honor for this important discovery. His first essay is entitled Everything Material under the enclosure of the Sky has Weight. He supposed that the earth occupied the center of the world. "Matter, filling at every point the space inclosed under the curvature of the sky, is continually urged by its own weight toward the center of the world. True it is that earth, being the heaviest, promptly occupies that place, and, forcing its contraries into retreat, makes water, second in weight, also second in place; so that air, driven from the lowest and the second place, is confined to the third, leaving to fire, the least ponderous of all, to abide in the highest region." Thus Jean Rey showed very precisely that all bodies have weight, that there is nothing light in Nature, and "no upward movement that is natural." Let us give his own words: "I say, if there was a channel from the center of the earth up into the region of fire, open at both ends and full of the four elements, everything in its usual place, that, on drawing the earth down, water would descend to occupy its place, leaving its own to the air, and the air leaving its place to fire. Then, withdrawing the water from that place, the air would come down to fill it; and this, too, being taken away, the fire would take possession of the vacant space and fill the whole channel, descending to the center, just by that being removed which prevented its doing so. Those ​who say that this would be done to avoid a vacuum do not say much. They point to the final cause, and this demonstration concerns the efficient one, which rules that there can not be a vacuum." Key's book, however, while it marked an immense progress in science, contains some considerable errors. Thus, he undertakes in his fifth essay to show, by the acceleration of the motion of falling bodies as they descend, that fire and air are heavy, and he attempts to prove by an ingenious but fallacious demonstration that they are forced down more and more rapidly by the increasing weight of the air and fire above them.
Having tried to "impress upon everybody's heart that air has weight," Rey announced the proposition, then new to science, deduced from this principle, that "weight is so closely joined to the primal matter of the elements, that changing from one to another they always keep the same weight. The weight which each portion of matter takes from its cradle it will carry to its grave. In whatever place, under whatever form, and to whatever volume it may be reduced, always the same weight." This principle, which he discovered more than a century before Lavoisier, was confirmed by a curious experiment of Brun's, who in 1644, having constructed a distilling apparatus, hermetically sealed, inclosed within it wood of guaiac, box, or oak, weighed the whole, and distilled it. The wood was destroyed; but a new weighing, made at the end of the experiment, showed that the total weight of the apparatus had not changed during the distillation. The experiment was a delicate one, and proves that they knew how to work in Rey's time. Mistakenly believing that water could change into air, Rey constructed an apparatus for determining what volume of air a given quantity of water would form. It consisted of a bulb (æolipile) in which water could be boiled, connected by a tube with a cylinder open at the top; a piston was worked in this cylinder. The piston was brought down to the bottom of the cylinder. Heat was applied to the æolipile and the water was made to boil or was "transformed into air"; the piston of course rose, under pressure of the steam or "water air," and the capacity of the part of the cylinder below it showed the volume of the air that was supposed to be formed. Then the æolipile could be removed, the opening from it into the cylinder stopped up, and the cylinder exposed to cold, when the piston would be forced down and the vapor frozen or turned into water. Unfortunately for himself, Rey did not personally try this experiment, or he might have anticipated Papin by half a century. But not more than a year after the publication of his essays—September 1, 1631—Père Mersenne said: "As to the experiments with the æolipile, I have made them; but it is a false imagination to suppose that the water which issues from ​it is turned into air; it still remains water, and will naturally return to itself."
Resuming his study concerning the weight of the air, Rey observed that his predecessors had failed to find it because they had weighed the air in itself: "Balancing the air in the air itself, and not finding weight, they have thought that it had none. But let them balance water (which they know is heavy) in water itself, and they will find no weight there too; it being a fact that no element has weight when balanced in itself. Everything that is weighed in the air and everything that is weighed in water should, for an equal volume, have as much more weight as it has more matter than the air or the water in which the balancing is done." Air, he said, could be made heavy by mixing it with some foreign matter having more weight; by compressing its particles; or by removing the lighter portions. In demonstration of the first principle, Rey determined by experiment that moist or cloudy air was heavier than dry air; of the second, he showed that, if a globe was filled by a strong draft of air from a bellows, it would be heavier than the same globe "empty." He even tried to make use of compressed air in the construction of a wind arquebus, but he did not carry out his idea; and the honor of making this invention practical belongs to the Sieur Marin Bourgeois, of Lisieux. Inversely, Rey observed that if one takes a glass vial cold, warms it a little on a chafing dish, and weighs it, he will find that it weighs less, because air has gone out from it; and in order to find how much, the pipe should be put, still warm, into water, which it will suck up till as much water comes into it as air has gone out of it. Rey was, however, not the first who had observed this fact, for Drebbel had anticipated him. The converse of these principles was also enunciated by Rey, viz., that the weight of air may be diminished by purifying it from heavier foreign matter, by extending it to ampler limits, and by extracting its heavier parts. "Even the balance sometimes deceives"; for, "if we examine the balances, cases may be found in which the object weighed will appear heavier or lighter without adding or subtracting foreign matter; as when it has been contracted or expanded." In support of this view, Rey cited as examples the cases of a ball of feathers tightly tied up, which will weigh more than the same feathers loose; and of two ingots, one of gold and the other of iron, which will balance one another without having the same absolute weights, "for the gold occupies a smaller volume for equal weight, and consequently displaces less air." These views were confirmed about 1650 by the inventions of Otto von Guericke.
Rey was now able to answer the question put to him by Brun, and to explain the cause of the increase of weight shown ​by tin and lead when they are calcined. "Now," he said, "that I have made my preparations, that is, have laid the foundations of my answer to his question" (as to the source of the seven ounces which the two pounds and six ounces of tin gained when heated for six hours; the difficulty of the problem was enhanced by its being necessary also to find the other matter required to compensate for the loss which the tin sustained through expansion in heating): "to this question, then, resting on the formulations already laid, I answer and maintain gloriously, that the increase in weight comes from the air, which has been thickened in the vessel, made heavy, and in no way adhesive, by the vehement and long-continued heat of the furnace; which air mingles with the earth (the frequent stirring aiding this) and attaches itself to the smallest particles; not otherwise than water makes sand heavy when sand is wet and the mass is stirred, by moistening and adhering to its smallest grains."
Several authors had already spoken of the increase of weight in metals on calcination. Cardan, in his Traité de la Subtilité, tried to explain the increase of the weight of lead in the formation of white lead by saying it was because the lead died and lost the celestial heat which was its soul and made it lighter; and added that an animal is always heavier dead than living. Rey remarked, in answer to this, that lead is void of life and can not be compared with the body of an animal, and showed that it was easy, by a known process, to recover the lead from its earth. Further, "nothing increases in weight except by the addition of matter or by contraction of volume," and this can not take place in the present case, even under Cardan's hypothesis, for the celestial heat in disappearing takes away matter, while on the other hand the volume increases perceptibly through the whole duration of the experiment. It will be noticed that Rey shared in the prejudice of his time in regard to the weight of animals increasing after their death, and with him many of the learned men of the period. Père Mersenne was the first to refute this error. He ascertained by experiment that a dog and a hen weigh more, though very little more, alive than dead, and wrote to Jean Rey, September 1, 1631, "You can yourself try the experiment without losing any of the blood, or a hair, or a feather, of the animals, by smothering them, as we have done."
Scaliger had undertaken to refute Cardan's assertions, and said that the increase in the weight of the calcined lead was caused by the fire consuming its aerated particles, comparing lead with the tile, "which is heavier baked than unburned." Nothing could be more simple than Rey's answer: "If the lead loses airy particles, would it not diminish in volume? On the contrary, it increases. And then, if this reason is correct, why do not ​stones and plants increase in weight when they are calcined? I add, finally, that air which is forced into a globe full of it, coming out diminishes the weight of the vessel instead of increasing it, as Scaliger believes." He rejected the comparison of the lead with the tile, saying, "The tile increases in weight by the shrinking of its extent; the lead by the matter that is added to it."
Cæsalpin had supposed, as Libarius records, in explanation of the phenomenon, that the soot produced by the fire struck the roof of the furnace and fell back upon the matter. Rey answered that the soot would blacken the lead instead of communicating a white tint to it. Moreover, if this were the cause, the production of earth might be carried on indefinitely by keeping up the fire, which was not the case. Libarius said that even apprentices in chemistry would laugh at Cæsalpin's theory.
Rey also showed that the increase in weight could not come from the iron vessel in which the calcination took place, for the earth would not continue white in contact with the dust of iron; besides, the vessel would be consumed in two or three operations, instead of being serviceable every day for several years; and, finally, if it was so, we should obtain from a very small quantity of tin or lead a very large quantity of earth, which is contrary to the experiment. Furthermore, a German chemist, Modestinus Fachsius, who also occupied himself with the question, concluded from the examination of the metals, the cupel, the lead, and the metal under trial, that all are heavier after the calcination than before they were exposed to the fire.
Deschamps assumed that the increase of weight was due to vapors of charcoal traversing the vessel. Rey answered that such vapors could not traverse a globe of glass, a plate of tin, or an earthen pot, because boiling water, sauces, and potages were not infected by them. How, then, could they traverse an iron vessel? Even if they did, why should they stop in the earth instead of going on?
Deschamps did not stop with this, but insisted that charcoal had two parts or natures, a vegetable and a metallic nature, and that each of them had two others, one fixed and the other volatile. The fixed part remains in the ashes, from which a fixed salt can be obtained by washing; but the volatile part, being of a mercurial nature, ascends around the vessel; and he made the objection to Rey's proposition that "the volatile part, lifted up on the wings of moisture, meeting the air which is directly on the vessel, being more rarefied and less heavy than the vapor that issues from the coal, is taken up by that in the vessel, and attaches itself by a close sympathy to the fixed salt of the earth of tin, which, having taken a certain quantity of it, and being, as it were, satiated, rejects the surplus." This observation, purely theoretical and made by ​a man of science, has a curious appearance now, but was all in place in Rey's time. Rey, who had answered the other objections by argument, had recourse this time to experiment. "If a furnace is built in a wall separating two rooms, in such a way that the vessel shall be on one side and the ventilating registers and doors for feeding in coal on the other, I maintain that the increase in weight will still take place, although no vapors can enter the chamber containing the vessel. I have confirmed this by an experiment which I made at the forges of Jean Rey, Lord of Perrotasse, my elder brother, where I found the increase in tin, which I calcined on a pig, as they call it, or an ingot of sixteen or twenty quintals of iron, at the instant when, coming out of the furnace, it was cast into its mold; for it can not be said that vapors of coal contributed anything to it. Therefore, the volatile salt can not be accepted in this case,"
Finally, with a single experiment Rey swept away all the objections in a lump. "I have just read in Homerus Poppius," he said, "in the third chapter of his book entitled Basilica Antimonii, of the new way that he practices in calcining antimony. He takes a certain quantity of antimony, weighs it, and having pulverized it, puts it in the shape of a cone on a marble; then takes a burning mirror, holds it in the sun so as to bring the pyramidal point of the reflected rays upon a point of the cone of antimony, which fumes abundantly, and in a little while the antimony, touched by the rays, is turned into a pure white earth, which he separates with a knife and turns the rays upon the rest till all has been turned white, and then the calcination is done. It is a wonderful thing that, although in this calcination the antimony loses much of its substance in the vapors and fumes that exhale from it copiously, its weight increases instead of diminishing. Now, if we ask the cause of this increase, will Cardan say that it is the disappearance of the celestial heat? That has been infused more largely by means of the solar rays. Will Scaliger say that it is by consumption of the airy parts? Thinning into earth and increasing in volume, it forces more in. Will Cæesalpin allege his soot? There is no fire to produce any soot. Does the vessel give up any of its own substance? Indeed, the rays are conducted so directly upon the matter that they do not touch the marble. Do you speak of the vapors of charcoal? No charcoal is used in this transaction. The volatile salts which have been so ingeniously brought forward lose here all their savor and grace. Perhaps moisture will be suggested, as has been recently done by some one. But where can it come from? From the marble? No, no, that is not conceivable. From the air? Still less; for the operation is best practiced in the warm days of summer, in the most violent heats. of the dog star."
​The final objection to his theory was one of Rey's own suggestion: Why does not earth go on increasing in weight indefinitely? Because "the thickened air attaches itself to it and continues to adhere to the most minute of its particles, so that its weight goes on increasing from the beginning to the end; but when it is all enveloped in air it can not take any more." He concludes then, and terminates his treatise by declaring with pride that he has found the real way of the truth, breaking the road for his successors, and advising them not to go astray from it.
This is the summary of the works of Jean Rey. A skillful experimenter, he knew how to use the balance, and it was the balance that suggested to him the result of his experiments. His book is a brief one. A single principal experiment is described, a single object is pursued in it. But he made two great advances in science. He discovered the weight of the air, being the first to publish that hypothesis, and verified it by experiments in chemistry and physics. The increase of the weight of lead and tin on calcination had been noticed for a long time by the alchemists, and even Galen knew of it. But nobody before Rey found that the cause of that increase in weight came from the air from that thickened and heavy air. It was certainly a remarkable achievement to announce such a fact at a time when chemistry had made so little advance. No gas was yet known; and it was not till about 1719 that a misunderstood man of science, Mortrel d'Élément, found means to decant air through water into bottles, and taught in a public lecture in Paris "how to make air visible and perceptible enough to measure it in pints or in whatever quantity you will." It was not his fault, therefore, that he did not advance further.—Translated for The Popular Science Monthly from the Revue Scientifique.