INTRODUCCIÓN

Life and career^{1,2,3,4,5,6,7,8,9,10}

Benjamin Thompson (Fig. 1), afterwards Count Rumford, was born on 26 March 1753 at North Woburn, Massachusetts, the only son of Benjamin Thompson and Ruth Simonds, small village farmers in New England. His father passed away when he was three years old; his mother remarried and reared a large family.⁴

Fig 1.
Benjamin Thompson, Count Rumford (1752-1814).

Thompson went to school at Woburn, at Byfield, and then at Medford. After leaving school at the age of thirteen he worked as an apprentice, first to John Appleton, then to Hopestill Capen, storekeepers selling imported dry goods, and then to Dr. Hay. While working for Hay he attended lectures in natural philosophy at the College of Harvard.⁷ For some time he worked as a schoolteacher at Wilmington and at Bradford, Massachusetts; in 1772 Coronel Timothy Walker, a local clergyman, invited him to teach in Rumford (now Concord), New Hampshire. Walker’s wealthy daughter, Sarah (1739-1792), who had recently become widowed, fell in love with Thompson and within four months they were married. Thompson settled down as a landowner farmer and scientific surveyor of the local country, while cultivating the friendship with John Wentworth (1737-1820), the royal governor of the colony of New Hampshire, an enthusiastic experimenter with agricultural products. In 1773 the governor made him a major in the New Hampshire militia, an appointment that infuriated the professional soldiers of the regiments.⁷

Thomson embraced the Royalist side in the early part of the American War of Independence; his wide knowledge of the local country made him very useful to the British commander in Boston. His behavior and activities arose the suspicions of the settlers and, as a result in 1775 Thompson was summoned to the local committee of safety and accused of being hostile to American freedom. Although the case was dismissed, a menacing mob surrounded his house and forced Thompson to flee to Boston, leaving his wife and only daughter, Sarah, behind. In March 1776 the British army withdrew from Boston and Thompson sailed for England in the frigate bringing the news from General Thomas Gage (1720-1787), the highest-ranking British officer in the Massachusetts Bay colony, to Lord George Germain (1716-1785), the Secretary of State for the Colonies.⁷ Germain took Thompson under his care and first appointed him as his private secretary and then to several important offices, among them, secretary for Georgia (1779), Inspector of all clothing sent to America, and Under-secretary for the Colonies (1780). While in London Thompson proposed to recruit a regiment in America for the service of the King; eventually he was sent to New York to carry on this mission, being appointed Lieutenant Commandant of Horse Dragoons of New York, After the signature of peace treaty between England and America (1783) Thompson returned to England, and soon after retired from the army as colonel, with half-pay.⁷

In 1784 Thomson traveled through Europe and at Strasburg befriended the Elector Karl Theodor, king of Bavaria. The Elector took him into his service and appointed him successively his aid-de-camp, his chamberlain, a member of his council of state, and lieutenant-general of his armies. According to Brown³, Thomson carried on all these positions simultaneously, becoming the powerful functionary in Bavaria, second only to the Elector. Among the many activities he carried on were reorganization of the military establishment, improvement of relations between officers and low rank soldiers and their feeding and clothing, as well as setting garrisons to work growing vegetables for their own use and for the workhouses. He cleared Munich of the beggar plague that affected the city and put them to work making clothing for the army, while providing them with nourishing meals and schoolteachers for their children. Large quantities of soup were made and distributed either by means of tickets, or sold at a very cheap rate. These activities led him to study the science of nutrition and the improvement of fireplaces and stoves, cooking tools (such as stove fuels, pans roasters, pots), etc. etc. He introduced large-scale farming of potato into Bavaria and incorporated it into all of his recommended menus. To feed the maximum number of people with the minimum cost, Rumford experimented with many types of nutritious soups until he arrived at the so-called Rumford Soup, based on barley, peas, and potatoes. He also published a long paper containing many recipes for the preparation of satisfying meals, among them Indian pudding, apple pudding, tagliati macaroni, and potato salad, and encouraged the drinking of coffee as an alternative to alcoholic drinks. Interesting enough, he promoted eating slowly, claiming that this made food more satisfying (a fact recommended today for those wanting to diet). Among the many institutions of public benefit he instituted in Bavaria, is the House of Industry at Manheim, the Military Academy of Munich, and schools of industry for the wives and children of the soldiers, and public gardens. The most famous of the latter is the still existing Munich English Garden.⁷

For these useful services, the King of Bavaria conferred on him several orders of knighthood, paid him lavishly, and in 1793 created him Count Rumford (after the old name of Concord, New Hampshire, in which he was born) and an annual pension of £1,200.⁴

In 1799, after a stay of about twelve years in Bavaria, Rumford returned to England, where he stayed for about two years. In 1802 he went back to Paris and three years later he married Marie Anne Paulze Lavoisier (1758–1836), the wealthy widow of Antoine-Laurent Lavoisier (1743-1794). This marriage was not successful mostly because Rumford’s disdain for social life. After the divorce (1809) Rumford move to Auteuil, near Paris, where his daughter joined him in 1811. He died there on 21 August 1814 and was buried in the local cemetery. Countess Rumford, his daughter, returned to America and died in 1852.⁷

In his will he bequeathed the annual sum of one thousand dollars and some of his properties to Harvard University to establish a chair to teach "the utility of the physical and mathematical sciences, for the improvement of the useful arts, and for the extension of the industry, prosperity, happiness, and well-being of society." He suggested the establishment, and brought to reality, the Royal Institution of Great Britain.¹¹ In 1796 he founded two prizes, to be annually awarded by the Royal Society of London and the Philosophical Society of Philadelphia (American Academy of Arts and Sciences of Boston), to the author of the most important experiments on heat and light.⁴

Rumford received many honors and awards for his scientific and public activities. He was Count Rumford of the Holy Roman Empire and the King of Poland decorated him with the Order of Saint Stanislaus of Poland, with rank White Eagle. He was an honorary member of the Royal Society and of the Royal College of Physicians of Edinburgh, a member of the Academies of Munich, Manheim, Berlin, the Royal Irish Academy, the Irish Society for the Encouragement of Arts, the American Philosophical Society of Philadelphia, the American Academy of Arts and Sciences in Boston, and one of the eight Foreign Associates of the Institut de France. He received a gold snuffbox as a tribute for this support in restructuring the culinary establishment of Heriot’s Hospital.

Rumford’s scientific curiosity, acute observation mind, and numerous military, public, and political activities led him to carry on research in a wide variety of subjects. For example, from the manufacture of weapons, particularly cannons, came papers about gunpowder, its force and measurement, including an improvement of Robin’s procedure ^[1]; the conversion of mechanical work into heat; experimental evidence against the phlogiston theory, and the proof that heat was transferred by molecular vibration.^{12,13,14,15,16} The need to improve the lighting conditions in dwellings and public buildings led to his studies on the properties, nature, and measurement of light, and the design of an improved lamp.^{17,18,19,20,21} Observation of natural phenomena and the welfare of soldiers, drove him to examine the mode of heat transfer in different media and its consequences upon climate; to the design of an apparatus for measuring thermal phenomena, the study of combustion phenomena and the design of improved stoves and chimneys.^{22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37} Others significant contributions were related to photosynthesis,³⁸ humidity,³⁹ and surface phenomena.⁴⁰

SCIENTIFIC CONTRIBUTION

Thomson published more than 80 papers on a variety of subjects in physics, chemistry, thermodynamics, and climate. A few of them are described below.

Light phenomena

Photosynthesis

Jean Ingenhousz (1730-1799) had discovered that the leaves of plants living under water gave of oxygen when exposed to the rays of sun,⁴¹ and Joseph Priestley (1733-1804) had observed that when water became green it always yielded more of this gas than common water.⁴² These experiments had led to the theory that vegetables decompose water, retaining the hydrogen and giving out the oxygen, and that by this process the oxygen taken from common air by animals and combustion was restored. In his paper about the production of dephlogisticated air (oxygen) from water^38,43 Rumford wrote that since he was not completely satisfied about the explanations provided for the results of Ingenhousz, he had decided to conduct some experiments to elucidate the causes. He begun by mentioning his previous findings that raw silk exposed to the action of light “possessed the power of attracting and separating air from water in great abundance”³⁹, and that it appeared to him of interest to examine the properties of the air released. He remarked that the purpose of this work was to report results, without applying them to the confirmation or refutation of the results obtained by other scientists. Thus, in speaking of the air produced upon exposing raw silk in water to light, he would sometimes mention it as being yielded by the silk, and other times, as furnished immediately by exposing water, which previously had turned green (decomposed); though it was probable that in both cases the green matter played a very important part in the production of this.³⁸

In Ingenhousz's procedure, plants were grown inside inverted glass globes full of water and the released gas collected and analyzed for its oxygen content. Rumford’s initial experiments followed Ingenhousz’s technique to collect a sufficient quantity of the air separated from water by silk to determine its quality by testing it with nitrous air (nitrous oxide). He promptly found that this setup made it very difficult to compare the volumes of gas released. He therefore modified it so that the gas displaced water, which could be easily collected as an overflow and therefore continuously measured during the advancement of the experiment. For this purpose, he filled a transparent glass globe with clear spring water and then introduced into it a certain amount of raw silk, which had been previously washed in water in order to free it from air. The globe was then inverted and put under water in a glass jar containing water of the same source, and exposed it to the action of sunlight. He collected all the gas released during a period of four days. The gas obtained was separated and mixed in 1:3 volume ratio with nitrous air (nitrous oxide), prepared by reacting fine copper wire in smoking spirits of nitre (KNO3), and then diluted in water. The substantial reduction in volume that took place proved that this air was actually very pure dephlogisticated air. Introduction of a small wax taper in the gas inflamed it immediately, with a very bright and enlarged flame. The water remaining in the flask lost part of its transparency and changed its color to a very faint green. Rumford also indicated that when the sunlight was very bright, the quantity of air released was not only larger but also of superior quality. The same experiments conducted in the dark did not produce any measurable quantity of gas.³⁸

Rumford then carried out 27 experiments under different conditions, for example, in total darkness, total darkness and heat, exposition to light and with the globe immersed in an ice and water mixture, the action of artificial light instead of sunlight, using other materials (wool, fine fur, cotton, human hair, and linen), submerging fresh healthy vegetables in water, changing the number of days exposed to sunlight, amount of silk added to a given amount of water, etc. etc.

Microscopic examination of the resulting water in an experiment done with poplar cotton showed the presence of a large number of animalcules (microscopic aquatic microorganisms), exceedingly small and of nearly a round figure. Rumford remarked that he had had been unable to understand the part these animalcules played in the operation of purifying the air in water. He stated that Priestley had found that many animal and vegetable substances putrefying or rather dissolving in water, in the sun, caused the water to yield large quantities of dephlogisticated air. Rumford believed that the silk and other materials he had employed did not participate (considered as chemical substances) in the process pure air production by water. They merely acted as mechanical aids in separating the air from the water by providing a suitable surface for the air to attach itself to. To prove this point, he performed additional experiments in which he substituted the silk by fine flexible threads of glass (used for producing brushes and artificial feather). The results confirmed his thoughts: a large amount of air was released on exposure to sunlight.³⁸

In a postscript to his paper, Rumford wrote that that his experiments proved that the dephlogisticated air produced by exposing fresh vegetables in water to the action of sunrays resulted from the removal of the air contained in the water, contrary to the generally accepted opinion (Ingenhousz’s) that it was elaborated in the vessels of the plant. In his own words, “that the fresh leaves of certain vegetables exposed in water to the action of sunrays, cause a certain quantity of pure air to be produced, is a fact which has been put beyond all doubt, but it does not appear to me to be by any means so clearly proved, that this air is elaborated in the plant by the “powers of vegetation”…phlogisticated or fixed air (nitrogen) being first absorbed or imbibed by the plant as food, and the dephlogisticated air (oxygen) being rejected as an excrement, for besides that many other substances…in which no elaboration…can possibly be suspected to take place, cause the water…to yield dephlogisticated air as well as plants…” As a further argument he indicated that experiments done by others (mainly Ingenhousz and Priestley) had indicated that fresh healthy leaves of vegetable, separated from the plant, and exposed to the action of sunlight, appeared to furnish air only for a short time; after a day or two the leaves changed color and ceased to yield air. The latter result was conceived to arise from a destruction of the power of vegetation (the death of the plant). He then described the results of four additional experiments that confirmed that the leaves ceased to furnish air, yet, after a certain time they regained this power and furnished more and better air than at first.³⁸

Rumford concluded his paper suggesting that the manifestations he had described could be accounted for by “assuming that the air produced in the different experiments had been generated in the mass of water by the green matter, and the leaves, the silk, etc; did no more than assist in making its escape by affording a convenient surface to which it could attach itself…[or] by supposing the green matter to be a vegetable substance, agreeable to the hypothesis of Priestley, that attaching itself to the surfaces of the bodies exposed in the water it grows…exerting its vegetative powers…and produced the air.’’ He rejected the second possibility because microscopic examination at the time when there was an abundant release of air, showed that the absence of anything that could be considered to be of vegetable nature. The “coloring of the water was a result of the assemblage of a large number of animalcules, without anything resembling tremella or that kind of green matter, or water moss, which forms upon the bottom and sides of standing water”.³⁸

His paper ended with the following comments: "Perhaps all the appearances above described might be satisfactorily accounted for, by supposing the air produced in the different experiments to have been generated in the mass of water by the green matter; and that the leaves, the silk, etc., did no more than assist it in making its escape, by affording it a convenient surface to which it could attach itself, in order to its collecting itself together, and taking upon itself its elastic form. The phenomena might likewise be accounted for by supposing the green matter to be a vegetable substance, agreeable to the hypothesis of Dr. Priestley, and that attaching itself to the surfaces of the bodies exposed in the water, as a plant is attached to its soil, it grows; and, in consequence of the exertion of its vegetative powers, the air yielded in the experiment is produced. I should most readily have adopted this opinion, had not a most careful and attentive examination of the green water, under a most excellent microscope, at the time when it appeared to be most disposed to yield pure air in abundance, convinced me, that, at that period, it contains nothing that can possibly be supposed to be of a vegetable nature. The colouring matter of the water is evidently of an animal nature, being nothing more than the assemblage of an infinite number of very small, active, oval-formed animalcules, without anything resembling tremella (a parasitic fungi), or that kind of green matter, or water moss, which forms upon the bottom and sides of the vessel when this water is suffered to remain in it for a considerable time, and into which Dr. Ingenhousz supposes the animalcules above-mentioned to be actually transformed".^38,43

His paper drew considerable criticism; two years later Jean Sennebier (1742-1809) repeated Rumford’s entire set of experiments and concluded that they were mistaken wrong and that “it was probably the air contained in the water which separated in the Count's experiments".^44,45

Light intensity and measurement

In a paper published in 1794,¹⁹ Rumford described his experiments comparing the intensity of the light of a clear day with that of a common wax candle. He let the light from the north to fall at an angle of about 70 0 upon a sheet of white paper, and also the light of candle in such a position that its ray fell upon the paper in the line of reflection of the daylight. He then put a cylinder of wood about one-half inch diameter at about 5 cm from the surface and was quite surprised to find that the two shadows projected by the cylinder on the paper instead of being colorless, the one corresponding to the beam of daylight was blue and that to the candle was yellow. Approaching the candle to the paper made the blue shadow deeper blue and the yellow fainter. Removing it far away caused the opposite effect, the blue became fainter and the yellow deeper. Rumford believed he understood why the shadow of the candle was yellow but not why the shadow from the sky was blue, particularly after repeating the experiments with skylight reflected from a roof covered by white snow, or using two candles and interfering the light of one with a pane of yellow glass. Once again one of the shadows was yellow and the other blue.¹⁹

Another unexpected result occurred when interposing a sheet of yellow or orange glass on the path of the candlelight. This time its shadow became orange while the blue shadow remained unchanged and the whole surface of the paper appeared tinged violet, approaching pink. These unforeseen results led Rumford to suspect that the colors of the shadows were simply an optical deception, owing to contrast, or some effect of the other neighboring colors upon the eye. Consequently, he performed a series of additional experiments changing the source of the light, its angle of incidence upon the paper, using two lamps instead of daylight and candle, or a flat ruler instead of a cylinder, looking with one eye at the shadows through a tube lined with black paper, etc. etc. Far from being able to observe any change in the shadow upon which his eye was fixed, he was unable to tell when the yellow glass was before the lamp, and when it was not, and could not discover in it the least appearance of any color at all. But as soon as he removed his eye from the tube and looked at the shadow with all its neighboring accompaniments, the original yellow and blue colors reappeared.¹⁹

Rumford concluded his paper stating his belief that “additional experiments may lead not only to a knowledge of the real nature of the harmony of colors…but also enable us to construct instruments for producing that harmony for the entertainment of the eyes in a manner similar to that in which the ears are entertained by musical sounds”.¹⁹

As a result of his work on the intensity of light, Rumford believed he had found a very simple and accurate method or measuring the relative quantities of light emitted by lamps of different constructions, candles, etc. etc. His procedure consisted in putting in a dark room two burning candles, lamps or other lights, separated one from the other by about 2 meters, and located at equal heights from the floor. The lamps shone on a piece of paper located at a distance of about 2 meters, in such a manner that a line drawn from the center of the paper, perpendicular to its surface, would bisect the angle formed by the lines drawn from the lights to that center. In this arrangement one light would be precisely in the line of reflection of the other. A small cylinder of wood, about ¼ in diameter and 6 inches long, was held in a vertical position at about 5 to 7 cm from the center of the paper and in such a manner that the two shadows of the cylinder corresponding to the two lights could be noticeably seen upon de the paper. One of the two lights was now moved (away or closer to the paper) until both shadows seemed to have the same density. In this situation the ratio of the real intensities of the two lights was be found to be equal to the ratio of the square of their distances to the center of the paper. Rumford named this apparatus photometer and afterwards modified its construction in order to reduce the errors to a minimum.¹⁸ He also used it made a series of additional experiments to determine the resistance of the air to light, the loss of light in its passage through plates or panels of different kinds of glass, the loss of light on its reflection from the surface of a plane glass mirror, the relative quantities of oil consumed and the light emitted by an Argand’s lamp ^[2], the relative quantities of beeswax, tallow, olive oil, rape oil, and linseed oil, consumed in the production of light, the transparency of flames, etc. etc. His results indicated that the flame was always perfectly transparent and permeable to the light of any another flame; that the quantity of light was not proportional to that of the heat, and that it did not depend, like the latter, upon he quantity of matter burnt, but rather upon the strength of the composition.^4,18

Nature of light

According to Rumford those who considered light as a substance emitted by luminous bodies, had been obliged to search for the source of that which was manifested in the combustion of inflammable bodies among those substances, which were known to concur in that process.³⁵ “Some had supposed that it was the inflammable substance which furnished it, others, that it was derived from the air (oxygen gas) employed in the combustion, which was supposed to be decomposed, and a later opinion appeared to be that it was furnished in part by the inflammable substance and in part by the oxygen”. Rumford commented that “if the light manifested in the combustion of inflammable bodies were in fact on of the chemical products of that process, as had been supposed, it was most certain that it ought to be found pre-existing in some of the bodies which were decomposed in that operation, and there was every reason to suppose that if that were really the case, that the quantity of light disengaged in the combustion of a given quantity of any given inflammable substance would be limited, and just as invariable as all the other chemical products of that process. But if the light was not a substance emitted by luminous bodies but a vibration and undulation in an ethereal fluid, analogous the vibration and undulation of the air, which is the immediate cause of sound. In this latter case, it was necessary to search for the cause of light, which was diffused by the flame of a burning body in the very high temperature of the particles of matter, which composed the flame. These particles must be considered as being luminous, in consequence of the action of the same cause, which rendered a cannon bullet luminous, which had been heated, red-hot in the fire. Since all known bodies ceased to shine in the dark at a given temperature, the hot particles which composed a visible flame ought to disappear completely ought to disappear entirely the moment they became cooled down to that temperature. Assuming this hypothesis to be true, we must no longer expect to find the quantities of light excited in the process of combustion to be in any constant ratio to the quantities of inflammable substance burned”.³⁵

In order to clarify this question, Rumford carried on a series of experiments to measure the intensity of light. Before doing so he improved the performance characteristics of his photometer. Among other things, he chose as standard light a wax candle of the first quality, 0.8 inches in diameter, burning with a clear and steady flame and consuming regularly 108 grains Troy of wax per hour. To this standard he assigned the value 100 0. He then reported the intensity of the light produced by an Argand lamp under different conditions and found that the quantities of light furnished were very far from being in a constant ratio to the quantity of oil consumed. After a series of experiments with other sources of light, for example, beeswax candles, Rumford remarked that “as long as the doctrine which supposes light to be a substance emitted by luminous bodies continues to be believed and universally taught, a great number deal of time will no doubt continue to be employed in useless researches concerning its supposed affinities and combinations”.³⁵

An interesting by-product of these researches was Rumford’s development of a modification of the Argand lamp, able to generate substantial more light than the original model. In it, the single burning ribbon was replaced by four wicks, each 1.6 in wide, placed vertically, one by the side of the other, at a distance of about 0.2 in, and so separated as to let the air come between them. This arrangement gave more light than six standard Argand lamps burning with their usual brilliancy. Some of these new lamps were found to give 5200 0 of light, equivalent to that of 52 wax candles of the best kind.^21,35

Chemical properties of light

Rumford had previously mentioned that he did not believe that light had chemical properties and that the visible changes produced in bodies by exposure to the action of the sunrays were not affected by a chemical combination of the matter of light with the bodies, but simply by the heat generated or excited by the light they absorbed.¹⁹ Finding that gold or silver could be melted by the heat (invisible to the sight) present in the air at the distance of more than 3 cm above the point of the flame of a wax candle,¹⁷ he was curious to know what effect this heat would produce on the oxides of those metals. He now conducted eight experiments in which he exposed a piece of white taffeta ribbon wet with solutions of the oxides of gold, silver, or magnesium, to the action of the flame of a burning candle, or the direct action of sunlight. For example, in the first experiment, he dissolved gold in aqua regia, evaporated to dryness the solution, and dissolved the residue in enough distilled water to avoid crystallization. He moistened a taffeta ribbon with the solution and held it over the clear bright flame of a wax candle. In a few seconds the wet spot turned purple and became indelible. Treatment with super oxygenated hydrogen chloride increased the intensity of the purple color, approaching it to reddish brown. Rumford was unable to find traces of gold. The same results were obtained when the ribbon was first dried in the dark, when the ribbon was made of paper, linen, or cotton, and also when using a solution of silver nitrate. In the latter case the spot was colored dark orange instead of purple. Rumford also reported that the heat released from the flame was enough to melt a very fine silver wire.¹⁷

In another experiment he moistened fine impalpable magnesia alba with the aqueous solution of gold oxide and exposed one half of it to sunlight, while keeping the other half in darkness. The magnesia exposed to sunlight begun almost immediately to change color, first becoming violet, and then, after a few hours, turned into deep purple. The portion kept in the dark retained the yellowish hue it had acquired from the solution, without the smallest appearance of change. When the wet magnesia alba was let to dry and then exposed to the sunrays, it acquired a faint violet hue, which turned deep purple if wetted again.¹⁷

The result of all these experiments led Rumford to conclude that light had little effect in changing the color of metallic oxides, as long as they were in a state of crystallization. The heat that was generated by the absorption of light had necessarily, at the moment of its generation, “exist in almost infinitely small spaces” and consequently, it was only in “bodies that are infinitesimal small” that it could produce durable effects. “The easiness, with which the metallic oxides could be reduced, by the dry via, by means of charcoal, showed that at a certain (high) temperature, oxygen was disposed to quit those metals in order to combine with the charcoal”. Hence, Rumford thought that gold might be rejuvenated by the wet via, by means of charcoal and sunrays; to test this point he performed an additional series of eight experiments in which he added small pieces of charcoal to the solution of gold in aqua regia, and exposed the mixture to the action of sunlight. Within a few hours the solution, originally bright yellow, became colorless and small specks of gold begun to appear on the surface of the charcoal and the inside of the tube. The same results were obtained with a diluted solutions of the oxide of gold, while holding the solution in the dark and heating to 210 0F; with a solution of silver nitrate mixed with charcoal and exposed to sunlight or kept in the dark and heated to 210 0F; and with solutions of gold oxide in sulfuric ether (ethyl ether).¹⁷

Heat phenomena

Conductivity

In 1786 Rumford observed that vacuum was a worse conductor of heat than atmospheric air and measured the relative conductivity or water and mercury under different circumstances.²² In a following paper²³he reported the relative thermal conductivity of fluids and solids of different nature, particularly of substances commonly used for clothing (i.e. raw silk, sheep wool, cotton wool, linen, fur of beaver, fur of a white Russian hare, and elder down) His experimental procedure was very simple. A thin mercury thermometer was introduced down to the center of a glass globe and the intermediate volume filled with 16 g of the material whose conducting power was to be determined. The whole apparatus was first submerged in boiling water and then in a freezing mixture of crushed ice and water, while the times of cooling were noted down. Since the interstitial space was always full with air, Rumford employed his apparatus to measure the conductivity of air, and used it as the comparison standard. For every substance he registered the time required to cool it from 700 to 100 0 Réaumur (87.5 0 to 12.5 0C). The total times for this temperature interval were 576, 1032, 1046, 1118, 1284, 1296, 1305, and 1315 seconds for air, fine linen, cotton wool, sheep wool, raw silk, beaver fur, elder down, and hare fur, respectively. Since the conductive powers were inversely proportional to these times, these results meant that the warmest substances were hare fur and elder down. The next set of experiments was carried on to determine the effect of the density of the material on the conducting power. For example, changing the weight of elder down loaded in the apparatus from 16 to 30 and to 60 grams, resulted in an increase in the cooling time from 1304 to 1472 and 1615 seconds, respectively. He also investigated the relative conductivities of the solid material and the air that occupied the interstices of the substance. His results indicated that this air played an important part in the act of confining heat (insulating power). Although individual particles of air were able of receiving and transporting heat, quiet air was unable of doing so, that is, in the latter state air was essentially a non-conducting material. In addition, there was a strong attraction between the particles of air and the fine hair or furs of animals, bird feathers, etc. These substances retained the air adhered to them even when immersed in water and subject to the action of a vacuum pump. These results explained why the finest, longest, and thickest furs, were the warmer.²³

Convection

Rumford’s discovery of the existence of convection currents in fluids was also accidental.^24,46 During a set of experiments on heat phenomena he used liquid thermometers having large diameter bulbs (10 cm). One of them, containing alcohol, happened to be placed in a window exposed to the sun. When looking at it “he saw the whole mass of its contents in a most rapid motion, in two opposite directions, up and down at the same time. These motions were rendered visible by some particles of fine dust that happened to be in the ball before it was filled. The tube was 43/100 inch in diameter, and upon examination with a lens, the rising current of spirit was seen to occupy the axis…of the tube, and the descending stream was contiguous to the sides. When the tube was inclined, the rising current occupied the uppermost side and the descending stream the lower. The velocities were perceptibly increased by wetting the tube with ice water; they became gradually less as the thermometer was cooled, and ceased then the fluid had acquired the temperature of the room, and the motion was greatly prolonged when the cooling of the bulb was impeded by wrapping it in furs or any other warm covering The same experiments, with motion of the same kind, as quite as rapid, were repeated with a similar thermometer filled with linseed oil”.²⁴

Rumford concluded that heat transfer was transferred in fluids “only by its being transported by virtue of their intestine motion produced by the change in specific gravity…and that there may be two ways of obstructing this propagation of heat, namely by diminution of their fluidity, which may be done by solution of any mucilaginous substance, or more simply, by impeding the motion of their particles…by mixing any solid substance…which is an imperfect conductor of heat and of an enlarged surface by being divided into small masses”.²⁴

The rate of heat transfer was reduced when increasing amount of a light substance were mixed with a liquid (water) or a gas (air). Thus feathers or hair would produce the same effects in water as in air, feathers or hair would produce the same effects in water as in air. Rumford concluded his paper with the comment that his findings about the poor conductivity of heat by water “could be used to explain the great operations (climate), which were regulated and performed on the surface of the globe”.²⁴

In a paper about the mode of propagation of heat in liquids³⁰ Rumford wrote that “when heat was propagated in solid bodies, it passed from particle to particle and apparently with the same velocity in every direction”, but his was not the manner in which it propagated through liquids. When a hot solid body was plunged in a cold liquid, the particles of the liquid in contact with the solid became lighter than the surrounding particles and rose to the surface of the liquid; the cold particles that replaced them at the surface of the hot body, repeated the same process. “All the particles thus heated by a successive contact with the hot body formed a continuous ascending current which carried the whole of the heat immediately towards the surface of the liquid, so that the strata of the liquid situated at a small distance under the hot body were not sensibly heated by it. In the same manner, when a solid body was plunged in a liquid hotter than the body, the particles of the liquid in contact with the body descended as a result of the increase of their specific gravity, and fell to the bottom of the liquid, and the strata situated above the level of the old body were not cooled by it immediately”. To this facts Rumford added the comment that although the viscosity of the liquids was still to great to allow to allow one of their particles individually being moved out of its place by any change of specific gravity occasioned by heat or cold, this did not prevent currents from being formed in the manner above described.³⁰

REFERENCIAS BIBLIOGRÁFICAS

1. Brown S C. Collected Works of Count Rumford, 5 vols, 1968–1970.

2. Brown S C. Rumford Bicentennial Lecture – Count Rumford, Physicist and Technologist. Proc Am Acad Arts Sci. 1853: 82; 266-289.

3. Brown, S C. Count Rumford, Physicist Extraordinary, Anchor Books, Garden City, New Cork, 1962.

4. Cuvier G. Recueil des Éloges Historiques lus dans les Séances Publiques de l'Institut Royal de France, 3 vols (1819–1827). Translated into English by Benjamin Silliman. Am J Sci. Arts. 1831: 19; 28-46.

5. Ellis G E. Memoir of Sir Benjamin Thompson, Count Rumford, with Notices of his Daughter, Boston, 1871.

6. Hale R. W. Some Account of Benjamin Thompson, Count Rumford. New England Quart. 1928: 1; 505-531.

7. Knight K. Thompson, Sir Benjamin, Oxford Dictionary of National Biography, Oxford University Press, 2004; online edn, Jan 2008 [http://www.oxforddnb.com/view/article/27255].

8. Sparks J. Count Rumford, The Library of American Biography, Charles Little and James Brown, Boston, 1840.

9. Thomas J. M. Sir Benjamin Thompson, Count Rumford and the Royal Institution. Notes Rec R Soc. Lond. 1999: 53; 11-25.

10. Urban S. Memoirs of Sir Benjamin Thomson, Count of Rumford. Gent Mag. 1814: 84; 394-398, July-December.

11. Tyndall J. Count Rumford, Originator of the Royal Institution. Notices of the Proceedings at the Meetings of the Members of the Roy Inst. 1882-1884: 10; 407–454.

12. Rumford Count. New Experiments on Gunpowder, with the Description of an Eprouvette. Phil Trans. 1781: 71; 229-328.

13. Rumford, Count, An Account of Some Experiments upon Gunpowder. Phil Trans. 1781: 71; 229-338.

14. Rumford, Count, Experiments to Determine the Force of Fired Gunpowder. Phil Trans. 87 (Part 2), 222-292, 1797; Nicholson J. 1797: 1; 515-518.

15. Rumford, Count, An Experimental Inquiry Concerning the Source of Heat which is Excited by Friction. Phil Trans. 1798: 88; 80-102.

16. Rumford Count. An Inquiry Concerning the Weight Ascribed to Heat. Phil Trans. 1799: 89; 179-194; Phil Mag. 1799: 5; 162-174.

17. Rumford Count. On the Chemical Properties that have been Attributed to Light. Phil Trans. 1798: 88 (Part 2); 449-468.

18. Rumford Count. Method of Measuring the Comparative Intensities of the Light Emitted by Luminous Bodies. Phil Trans. 1794: 84; 67-106.

19. Rumford Count. An Account of Some Experiments on Coloured Shadows. Phil Trans. 1794: 84; 107-118.

20. Rumford Count. Recherches sur le Chaleur Excitée par les Rayons Solaires. J Phys. 1805: 61; 32-39.

21. Rumford Count. Observations on the Dispersion of the Light of Lamps by Means of Shades of Unpolished Glass, Silk, etc. with a Description of a New Lamp. Nicholson J. 1806: 14; 22-38.

22. Rumford Count. New Experiments upon Heat. Phil Trans. 1786: 76; 273-304.

23. Rumford Count. Experiments on Heat. Phil Trans. 1792: 82, 48-80.

24. Rumford Count. An Account of the Manner in which Heat is Propagated in Fluids and its General Consequences in the Economy of the Universe. Nicholson J. 1797: 1; 101-106.

25. Rumford Count. On the Use of Steam as a Vehicle for Conveying Heat from one Place to Another. Roy Inst. J. 1802: 1; 34-45.

26. Rumford Count. An Account of a Curious Phenomenon Observed on the Glaciers of Chamouny, with some Observations on the Propagation of Heat in Fluids. Phil Trans. 1804: 94; 23-29.

27. Rumford Count. An Inquiry Concerning the Nature of Heat and the Mode of its Communication. Phil Trans. 1804: 94; 77-182.

28. Rumford Count. Investigations about the Temperature of Water at its Maximum Density. Nicholson J. 1805: 11; 225-233; Mém. Inst. Fr. 1806 ; 78-97.

29. Rumford Count. Experimental Investigations Concerning Heat. Nicholson J. 1805: 12; 65-75, 154-171.

30. Rumford Count. Inquiries Concerning the Mode of the Propagation of Heat in a Liquid. Nicholson J. 1806: 14; 335-363.

31. Rumford Count. Description d’un Nouvel Instrument de Physique (Thermoscope). Mém de l’Inst. 1806: 6; 71-78.

32. Rumford Count. On the Capacity for Heat or Caloric Power of Various Liquids. Phil Mag. 1814: 43; 212-218.

33. Rumford Count. Observations Relative to the Means of Increasing the Quantities of Heat Obtained in the Combustion of Fuel. Roy Ins. J. 1802: 1; 28-33.

34. Rumford Count. Inquiries Concerning the Heat Developed in Combustion, with a Description of a New Calorimeter. Nicholson J. 1812: 32; 105-125.

35. Rumford Count. On the Light Manifested in Combustion. Bib Britannique. 1812: 54; 3-26.

36. Rumford Count. Researches Upon the Heat Developed in Combustion, and in the Condensation of Vapours. Phil Mag. 1814: 41; 285-297, 434-444, 1814: 42, 296-307, 1814: 43; 64-69.

37. Rumford Count. On the Quantities of Heat Developed in the Condensation of Water Vapour, and in that of Alcohol. Phil Mag. 1814: 43; 64-69.

38. Rumford Count. Experiments on the Production of Dephlogisticated Air from Water with Various Substances. Phil Trans. 1787: 77; 84-124.

39. Rumford Count. Experiments to Determine the Positive and Relative Quantities of Moisture Absorbed from the Atmosphere by Various Substances under Similar Circumstances. Phil Trans. 1787: 77; 240-246.

40. Rumford Count. Expériences et Observations sur l’Adhésion des Molécules de l’Eau Entre Elles. Nicholson J. 1806: 15; 52-56, 157-159, 173-176; Bib Britannique. 1806: 33; 3-16.

41. Ingenhousz J. Experiments Upon Vegetables, Discovering Their great Power of purifying the Common Air in the Sun-shine and of Injuring it in the Shade and at Night, to which is joined a new Method of examining the accurate Degree of Salubrity of the Atmosphere, Printed for P. Elmsly in the Strand and H. Payne in Pall Mall, London, 1779.

42. Priestley J. Experiments and Observations on Different Kinds of Air, Pearson, London, 1778.

43. Brown S C. Count Rumford on Photosynthesis. Daedalus. 1955: 86; 43-46.

44. enebier J. Expériences sur l'Action de la Lumière Solaire dans la Végétation, Chez Barde et Manget, Genève, 1788. The pertinent material was exposed and discussed by Hassenfratz, J., Extrait des Expériences de M. Sennebier sur l’Action de la Lumière Solaire dans la Végétation. Ann Chim Phys. 1790: 1, 108-116.

45. Hassenfratz J. Extrait des Expériences de M. Sennebier sur l’Action de la Lumière Solaire dans la Végétation. Ann Chim Phys. 1790: 1; 108-116.

46. Brown S C. Count Rumford Discovers Thermal Convection. Daedalus. 1957: 86; 340-343.

47. Fordyce G, An Account of Some Experiments on the Loss of Weight in Bodies on being Melted of Heated. Phil Trans. 1785: 75; 361-365.

48. Cook W. A Proposal for Warming Rooms by the Steam of Boiling Water Conveyed in Pipes Along the Walls, and a Method of Preventing Ships From Leaking, whose Bottoms are.

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