determination of d003 by capillary gas...

Revista CENIC Ciencias Químicas, Vol. 45, pp. 199-210, 2014.

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William Nicholson Recibido: 16 de enero de 2014. Aceptado: 16 de marzo de 2014. Palabras clave: multiplicador de carga eléctrica, electrómetro, electróforo, inflexión y reflexión de la luz, hidrómetro de Nicholson, periódico de Nicholson, movimiento perpetuo, pez torpedo, electrólisis del agua. Keywords: electrical charge multiplier, electrometer, electrophorus, light inflection and reflection, Nicholson’s hydrometer, Nicholson’s journal, perpetual motion, torpedo fish, water electrolysis. RESUMEN. William Nicholson (1753-1815), un científico multifacético, sin educación universitaria, se caracterizó por un profundo sentido teórico y práctico, que lo llevó a descubrir la electrólisis del agua, proponer una simulación de los fenómenos eléctricos en peces como el torpedo y la anguila, a demostrar la imposibilidad del movimiento perpetuo, a construir una serie de instrumentos y reglas de cálculo para diversas aplicaciones, el estudio de diversos fenómenos eléctricos y ópticos, etc. etc. Fue el fundador y editor del primer periódico inglés (Nicholson’s Journal) para la publicación de artículos científicos, difusión de novedades científicas en Europa, resumen de artículos aparecidos en revistas científicas inglesas y europeas, así como de las sesiones de la Royal Society. Asimismo, tradujo al inglés las principales obras francesas sobre química de su tiempo. ABSTRACT. William Nicholson (1753-1815), was a polymath scientist, without formal university education, possessing a deep theoretical and practical sense, which led him to discover the electrolysis of water, to propose a model for simulating the electric phenomena taking place in fish such as the torpedo and the eel, to show the impossibility of perpetual motion, to build a number of instruments and sliding rules for different applications, to study several electrical and optical phenomena, etc. etc. He was the founder and editor of the first British paper (Nicholson’s Journal) devoted to the publishing of original scientific papers, the diffusion of European scientific news, summary of papers appeared in British and European scientific journals, as well as the sessions of the Royal Academy. He also translated into English the most important chemical books of his time. LIFE AND CAREER1-3 William Nicholson was born in December 1753, in London, the son of George Nicholson, a solicitor in the Inner Temple, and his wife, Hannah. At the age of nine he was sent to a boarding school in the North of Yorkshire, where he learned Latin, Greek, French, and the standard courses in mathematics, and showed ability in making mathematical and optical instruments, At the age of sixteen he left school and entered the service of the East India, as a midshipman, and made two voyages to China. After the death of his father in 1773, he left the sea and took an employment in the country trade in India. In 1776, he worked as commercial agent in Rotterdam for Josiah Wedgwood (1730-1795), the famous English potter, founder of the Wedgwood Company. Soon afterwards (1780) he settled in London and earned his living as teacher of mathematics, translator, and writer of compilations of his own. At about the same time he married Catherine Boullie; they had twelve children, of whom eight survived to maturity. In 1782, he published his Introduction to Natural Philosophy,4 in two volumes, which superseded John Rowning’s (1701-1777) A Compendious System of Natural Philosophy, which had been long used as an elementary textbook.5 Here Nicholson showed that in spite of lacking university education, he was highly conversant in physics, mathematics, chemistry, and mechanics. In the following years he published other books, such as a new edition of Ralph’s Survey of the Public Buildings of London,6 a translation of Maurice Benyowsky’s (1746-1786) Memoirs and Travels of Mauritius Augustus Count de Benyowsky,7 a translation of the History of Ayder Ali Khan,8 a Navigator’s Assistant Containing the Theory and Practice of Navigation9, an Abstract of the Arts Relative to the Exportation of

Jaime Wisniak Department of Chemical Engineering, Ben-Gurion University of the Negev,Beer-Sheva, Israel 84105 [email protected]

mailto:[email protected]


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Wool,10 a translation of Carl Gotlob Küttner’s (1755-1805), New and Complete Dictionary of the German Language of Englishmen11, etc. etc. In 1797 Nicholson began the publication of his own scientific journal, Journal of Natural Philosophy, Chemistry and the Arts, which continued to appear until 1813 when it was taken over by Alexander Tilloch’s (1759-1825) Philosophical Magazine. Nicholson’s journal was the first British periodical dedicated to the sciences, to publish original research papers, reviews, summaries of the contents of provincial and foreign journals, reports of scientific meetings at the Royal Society and elsewhere, etc. At the time when the debate about the phlogiston theory and the new chemistry of Antoine-Laurent Lavoisier (1743-1794) was at its highest point, Nicholson found the time to translate into English the most important chemistry books on the subject, among them, Kirwan, Fourcroy, et al. An Essay on Phlogiston, and the Constitution of Acids,12 Pajot des Charmes’s L’Art du Blanchiment des Toiles, Fils et Cotons de Tout Genre;13 Antoine François de Fourcroy’s Système des Connaissances Chimiques14 and Leçons d'Histoire Naturelle et de Chimie and its supplement,15 and Jean-Antoine Chaptal’s (1756-1832) Éléments de Chimie and Chimie Appliqué aux Arts;16 as well as publish his own works.17-20 In 1799, Nicholson opened a private school for teaching natural philosophy and chemistry to a class of 20 students; this enterprise did not last many years because most of his time was devoted by Nicholson to some public works such as the West Middlesex Water Works, and the water supply for Portsmouth, Gosport, and the borough of Southwark, as well as continue to publish more books. As written in one of his eulogies: “This truly ingenious and indefatigable man shared the common fate of projectors, to be continually employed without enjoying any material advantage from his labours. Though incessantly occupied in useful concerns, and ardent in promoting the interests of science, he was generally embarrassed in his circumstances; and notwithstanding his uncommon industry he lived and died poor”.2 On May 21, 1815, Nicholson died at his home after a long illness. Nicholson’s vast culture led to his election to several important organizations: In 1783, he was elected to the Coffee House Society, an informal group of scientifically inclined people; the following he was elected secretary of the same. In 1784, at the suggestion of Wedgwood, he was appointed secretary to the General Chamber of Manufacturers of Great Britain. In 1791, he became associated with the Society for the Encouragement of Naval Architecture. In 1801, Nicholson and Anthony Carlisle (1768-1842) were appointed to the committee for chemical investigation at the new Royal Institution, In December 1806, Nicholson was appointed engineer to the West Middlesex Water Works Company, but was dismissed the following year for neglecting his duties. Nicholson’s research covered a wide range of subjects. He carried on a large number of experiments on different aspects of electricity, its measurement, and its effects, for example, the construction of an improved version of the Bennet doubler of electricity (an amplifier of small electrical charges);21-24 a revolving doubler;25 excitation of electricity, the luminous appearance of electricity, and compensated electricity;26 an improved electrometer;22,27 instruments to distinguish the two kinds of electricity,28 an electric battery of mica,29 and speculations on the luminous phenomena of electricity.30 His most significant achievements in this area were the discovery of the electrolysis of water (together with Carlisle)25 and the explanation of the electrical behavior of the torpedo fish.31 He studied several optical phenomena,32,33the simmering of water,34 the light from candles and lamps;35 the so-called “perpetual motion.”36,37 developed an improved hydrometer,38 etc. etc. The practical use of his discoveries was translated into four patents and papers on the construction of slide rules and other calculation instruments.39-46

SCIENTIFIC CONTRIBUTION Nicholson wrote fifty odd papers and several books about a wide range of subjects. Most of the papers were published in his journal. Specific gravity One of the first papers published by Nicholson described a new apparatus he had constructed “for the easy and exact finding” of the specific gravity of bodies. He first gave a short historical review of the contribution of other scientists, such as Robert Boyle (1627-1691), Samuel Clarke (1675-1729), Daniel Fahrenheit (1686-1736), and George Fordyce (1736-1802) and Quin, and explained their instruments, and their advantages and disadvantages.38 He then proceeded to describe the new apparatus he had built [see Figure 1(a)]. The regular procedure for determining the specific gravity of a substance was to weigh it first in air and then submerged in water, while suspended from a hook. Nicholson’s apparatus consisted of a hollow copper ball A, of diameter 2.3 inches, attached to a dish (scale) B (1.5 inch diameter and weight 2.851 g) by means of a stem D made of hardened steel, and about 1/40th of an inch in diameter. The total weight of the copper ball and stem was 369 grains (23.911 g). A stirrup of iron wire, screwed to the lower extremity of the ball, carried another dish C, sufficiently heavy (105.88 g) to act as a counterweight and keep the instrument in a vertical position, particularly when floating in a liquid. The parts of the instrument were so designed that when 1000 grains (64.799 g) were placed in the upper dish B, the stem would sink in distilled water at

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60 0F to the point m in the middle of the stem (not shown). This step represented the calibration of the apparatus; for temperatures higher or lower than 60 0F the weight would be different than 1000 grains.

Fig. 1(a) To determine the specific gravities of solids that did not exceed 1000 grains in weight, the instrument was placed in distilled water, and the upper dish B was loaded with the sample and weights until the instrument against sunk to m. The difference of 1000 less the weight added represented the weight of the solid (W). The solid was now placed in the lower dish F and weights added in the upper dish B until the instrument against sunk to m. The weights now added (w) represented the loss in weight, which the solid suffered, or the weight of an equal bulk of distilled water of specific gravity. All these measurement were connected by the relation s/S = W/w, where s is the specific gravity of the solid. Nicholson added a note that the water itself and the temperature should the same for all the experiments, and a thermometer was supplied with the balance. 60 0F was suggested as a normal room temperature.38

In his book An Introduction to Natural Philosophy4, Nicholson added that his instrument had been found to be sufficiently accurate to give weights true to less than 1/20th of a grain (0.003 24 g). Nicholson’s hydrometer became very popular, particular among geologists, because its was portable, easy to use, and very accurate. Perpetual motion On May 23, 1797, a patent was granted to Richard Varley for a machine for a perpetual moving power.47 This patent was highly praised in The Monthly Magazine of July, 1797,48 in these words: “The ignorant and prejudiced part of mankind have in all ages attached a folly to the pursuit of various mysteries of nature and science, such as the ascertaining the length at sea, the variation of the magnetic needle, the transmutation of metals, the quadrature of the circle, the adhesion of metallic particles, the repulsion of atmospheric particles, the essential differences between bodies to the exclusion of their attributes, and perpetual motion. The last has been thought, in the general meaning of the term, to be the most chimerical, because all machines are composed of perishable substances. Mr. Varley’s discovery of a new perpetual power appears however, to promise as much utility as stem, wind, water, and any other force requisite for working mechanical apparatus”. A short description, accompanied by a drawing, was given of the apparatus. “Thus having described the machine, it appears that the principle of the discovery of the new power is effected by converging the weight of the atmosphere on a wheel in any other fluid, and by that means destroying the repulsive quality or reaction of the air.” This notice brought a prompt response of Nicholson, worded as follows: “I should be glad to give a description of Mr. Varley’s machine for producing perpetual motion, as requested by Mr. Notlem, of Wisbech, if an attentive perusal of the specifications enrolled in Chancery had [shown] me anything tending to improve the theory or practice


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of mechanics. The description in the periodical work he mentions is not sufficiently clear to [show] the whole of what the writer meant to explain, and I found the original equally imperfect. Mr. Varley’s notion, obscured by some extraneous and unimportant circumstances, appears to be, that if an exhausted cylinder be fixed to one part of the periphery of a wheel, and a piston fitted therein, the pressure of the atmosphere on this last, supposed to be attached to the wheel by a spring and chain (parallel to the tangent), will tend to drive it into the vacuum and, if prevented y the shortness of the chain, will draw the wheel round. It is obvious to any person acquainted with statics, that the pressures on this wheel must counterbalance each other, and cannot produce motion.” “It has always been easy to [show] the fallacy of schemes for perpetual motion in the particular instances; but I have met with no clear enunciation of this project so general as to include every possible scheme, and evidence its own absurdity. The difficulty of performing this seems to arise from a want of direct and concise demonstrations of the fundamentals principles of the lever and the equal pressure of fluid in all directions”.49

In a paper published shortly thereafter, Nicholson criticized as worthless, all the efforts invested in trying to develop a perpetual motion engine.36 In his opening statement he wrote that the “purpose of a perpetual motion machine was to cause a body or system of bodies to act in such a manner that the reaction shall be greater than the action itself, and by that mean generate force by accumulation of the surplus, or that the motion communicated be greater than that lost by the agent There is no doubt that numerous arrangements have been made, and still are labored at by various individuals, to produce a machine which shall posses the power of moving itself perpetually, notwithstanding the inevitable loss of force by friction and resistance of the air.” He then went on to prove the falseness of mechanical contraptions (and their variations) proposed by Conrad Shiviers, the bishop John Wilkins (1614-1672), the Marquis of Worcester (Edward Somerset, 1601?-1667), and John Theophilus Desaguliers (1683-1744), illustrated in Figure 1(b). For example, Desagulier’s sketch (a variation of the one proposed the Marquis of Worcester) consisted of a number of partitions, placed obliquely with respect to the radius, between the internal and exterior surfaces of two concentric cylinders, and containing identical spherical weights. Inspection of the figure showed that when the lower end of any particular cell was located at the lowest point, then the weights on the right hand side would rest touching the internal cylinder, while other will touch the external one. “If now the wheel was made to rotate counter clockwise, the internal weights will move towards the external surface, while the external weights move in the opposite direction. It would seem then, that the wheel would keep rotating indefinitely, but this was not the case, since the weights G and F, G, and E, I, and D were clearly in mechanical equilibrium because they were located at the same horizontal distance from the center. Using the geometrical theorem that if in two concentric circles tangents are drawn at the extreme points of a diameter of the internal circle, and continued until they intersect the larger circle, then the common center of gravity of the arc of the larger circle included between the tangents, and of the half periphery of the smaller circle, will be the common center of gravity of both circles. Hence, assuming that the balls are indefinitely numerous and small, the effective parts of the wheel will be in equilibrium, as well as the parts beneath the horizontal tangent of the inner circle”.36 Inspection of Figure 1(b)

Fig 1(b). shows that the number of weights and their momentum, will never be the same on both sides of the vertical passing through the center of the wheel: the ones on the left hand side have the largest momentum but their number is proportionally smaller than the ones located on the right hand side of the wheel. In simple words, the wheel will not turn because the total leverage on both sides is the same, or, the work done by a given weight falling from a given height is independent of the path and cannot be larger than the amount of energy required to return it to its original position. Three years later, Nicholson published another paper on the subject, this time rejecting the possibility of perpetual motions by means of the rise and fall of the barometer or the thermal variations in the dimensions of bodies.37 He


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repeated his claim that the flow of rivers, tides, wind, the thermometrical expansion of solids and fluids, and fall of mercury in the barometer, the hygrometric changes in organized remains, and every other of those mutations, which constantly took place in our surroundings, could be applied as first movers to mills, clocks, and other engines, and keep them working until worn out. In other words, the machine seemed to be operating incessantly, but it was not a perpetual motion apparatus; an external, probable variable agent, acting as first mover, was running it. He provided examples and drawings, of several first movers, moved by temperature changes acting on mercury, metal bars, etc., with variable lengths of change. As an example, consider the arrangement shown in Figure (1c) describing a first mover for a clock, and explained by Nicholson as follows: “AB represents the surface of mercury enclosed in a glass vessel built as a balloon and having its neck submerged in a cistern CD containing mercury. The receptacle is suspended from two chains K, L, which passes over the pulleys H, I, connected to the frame EF attached to the head of the balloon. The diameter of wheel G, which is placed between the bars E and F, is such that when the teeth on one side, for example E, are engaged, those on the other side (F) are free, and vice versa. If the atmospheric pressure decreases and the barometer rise from its cistern, the side E of the frame will move the wheel accordingly. When the pressure increases, and the barometer falls the teeth E will be drawn out of their bearing and those of F will connect with the wheel. If the wheel is connected a clock, it will serve to wind it up, and allow the clock to go for a longer time”.37

Fig 1(c). Some interesting aspects of the perpetual motion controversy are the following: (a) in 1775 the French Académie des Sciences resolved not accepting anymore proposals for solving the problem of the duplication of the cube, the trisection of an angle, the quadrature of the circle or the building of a machine able of perpetual motion;50 (b) the first law of the thermodynamics (conservation of energy) became accepted in the 1850s.51 and (c) the U.S. Patent Office decided that it would consider an application for a perpetual motion engine, only if accompanied by a working model. Electricity and electrical phenomena As mentioned above, Nicholson carried on a large number of experiments on different aspects of electricity, its measurement, and its effects. Here the author describes two of the most important ones. Electrolysis of water In March 20, 1800, Alessandro Volta (1745-1827) wrote a letter to Joseph Banks (1743-1820), President of the Royal Society; informing him about some striking results he had obtained in his experiences about the electricity generated by a simple contact between different metals and other conductors, liquids or humors (this letter was read before the Society on June 26).52 The main result was the construction of an apparatus able to afford a “perpetual current of electricity”, and which differed from other arrangements, in the manner it was built. The apparatus was built by taking any number of plates of copper (or better of silver), and an equal number of tin (or better of zinc), and a similar number of discs made of paper or leather, or cloth, or any wettable substance. The latter was soaked in pure water, a saline solution, or alkaline lye. The silver or the copper could be pieces of money. All these pieces were stacked together, in the repeating order one of silver, one of zinc, and one of wet card, in any number of units of the three pieces. This construction produced the same commotions generated by the Leyden jar or an electrical battery. For example, touching with the fingers both ends of the structure generated a perceptible electrical shock, as many


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times as the fingers were put in contact with it. The commotion was stronger as the number of pieces was increased. The apparatus was not only capable of providing a signal to a Cavallo electrometer connected to a condenser, and charging the latter enough to produce a spark. Volta added that his structure was similar to the natural electric organ of the torpedo fish and for this reason he had named it organe électrique artificiel (artificial electric organ, today voltaic pile). Volta described several different arrangements to multiply the same effect. For example, in the one he called wreath (or crown) of vases, a series of vases containing a conducting solution, were connected by metallic arcs, having one end made of silvered copper, and the other of zinc. As many vases could thus connected, taking care only that the entering metal was different from the one leaving the vase. Immersing one hand in one of the vases, and the other in another, was enough to feel the commotion in the body. Volta also described the physical reaction of the body when the contact was made through a wound, the tongue, the lips, the ears, etc, and commented that the strength of the signal increased if the solutions were heated. It seemed that heat made the body more conductive.52 Banks showed the letter to his friend Anthony Carlisle (1768-1842), who invited Nicholson to repeat Volta’s experiments. A pile made with 17 coins of half crown and a like number of pieces of zinc and pasteboard was found to reproduce exactly the results reported by Volta.25,53 Carlisle and Nicholson decided to carry on additional experiments to gather more information about this new phenomenon. Very early in May they noted that although the action of the instrument was freely transmitted through the usual conductors of electricity; glass and other non-conductors stopped it. The more significant finding occurred when a drop of water was put on the upper plate in order to improve the contact: a very small amount of gas, having the smell of hydrogen, was seen disengaging around the touching wire. This result led Nicholson to break the circuit by installing a tube filled with river water between two brass wires. A fine stream of minute bubbles was seen immediately to flow from the lower end of the wire connected to the silver, while the opposite point of the upper wire became tarnished, full deep orange, and then black. Reversal of the tube caused a reversal of the phenomenon. These changes could be carried on as many times as desired. After two hours of operation, the upper wire gradually emitted white filmy clouds, which towards the end of the process became pea green. Simultaneously, the lower wire constantly emitted gas. This gas, mixed with an equal amount of atmospheric air, exploded when exposed to a flame.25,53 Nicholson and Carlisle wrote that “they had been led by their reasoning…to expect a decomposition of the water”; but they were “extremely surprised to find that the hydrogen extricated at the contact with one wire, while the oxygen fixed itself in combination with the other wire at a distance of almost 5 cm. This new fact still remained to be explained and seemed to point at some general law of the agency of electricity in chemical operations”.25,53 An additional experiment done by Carlisle on May 6 showed further surprising results. Carlisle repeated the experiment with copper wire and litmus tincture and noticed that the oxidizing (zinc) wire changed the color of the litmus to red while on the other wire it remained blue. These results indicated that an acid was formed or that a portion of the oxygen combined with the litmus to produce an acid effect.25,53 The decomposition of water and oxidation of metallic wire suggested other experiments, for example, would this process also lead to the oxidation of metals known to be difficult to oxidize? To answer this question, the experiment was repeated inserting two platinum wires of different shape in the tube, and the apparatus operated for four hours. The silver side gave a plentiful stream of gas and the zinc one a less plentiful one; the larger stream was naturally assumed to be hydrogen, the smaller oxygen. No turbidity, oxidation, or tarnishing appeared. The same effects were noted with gold. The simple decomposition of water by platina wires, without oxidation, provided a means of obtaining (and collect) both gases separate from each other. The quantities of water displaced by the zinc side and the silver one were 72 and 142 grains, respectively.25,53 Torpedo fish Since ancient times it was widely know that some fish such as the torpedo or the electric eel, produced on contact painful effects similar to an electric shock. In 1773, John Walsh (1726-1795) read to the Royal Society a long paper giving a detailed description of the torpedo fish and its electrical organs, and demonstrated, for the first time, that the singular power of benumbing the sense of touch possessed by the fish was “absolutely electrical” and that it could only send a shock through conducting substances. He showed that the back and breast of the fish were in “different states of electricity” (plus and minus) and that he could use this fact to direct the shocks through a circuit of four persons or through a long wire held by two insulated persons; one touching the lower surface, and the other the upper. The effect ceased to exist if the wire was replaced by glass or sealing wax. Walsh added that it was surprising that the fish could give to an insulated person, forty or fifty shocks from the same part.54 Another paper by the surgeon John Hunter (1728-1793), followed the one by Walsh and giving a very detailed anatomical description of the torpedo;55 two years later, Hugh Williamson (1735-1819) reported similar experiments with the electrical eel (Gymnatus electricus), which had been caught in Guiana.56 According to Williamson, this eel had the extraordinary power of communicating a painful electrical shock to people who touched it and of killing its prey at a distance. Touching the eel with one hand, and at the same time holding the other hand at a small distance, a shock passed through both hands, as in the case of a Leyden jar. The same effect was noticed by a chain of eight or


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ten persons, the first of the series touching the eel and the last putting his hand into the water, at some distance from the animal. According to Williamson, the shock had to depend upon “some fluid”, which the eel discharged from its body. Since this fluid affected the same parts of the human body that were affected by the electric fluid, the shock given by this eel had to be the “true electric shock”.56 In the same year, Henry Cavendish (1731-1810) read a very extensive memoir to the Royal Society in which he reported his experiments on an artificial torpedo.57 Cavendish believed that although Walsh’ experiments left little doubt that the phenomena of the fish were caused by electricity, there were some circumstances which at first sight seemed to disagree with this conclusion. One of the principal objections to Walsh’s hypothesis was that a shock could be felt when the fish was under water or where the electric fluid could pass through a different passage than the person’s body. Cavendish answered this objection by pointing out that when a jar is electrified and a number of circuits connect the positive and negative sides, some electricity will pass through each, but “a greater quantity will pass through those in which its meets with less resistance, than those in which it meets with more…Discharging a jar by a wire held with both hands, the person does not feel a shock…(because) metals conduct surprisingly better than the human body …consequently…the quantity of electricity (passing) through the persons body” is a small fraction of the total, “so as not to give any sensible shock…When a person receives a shock from the torpedo he must have formed the circuit between the upper and lower part before it begins to throw electricity from one side to the other…The only way in which a spark could be perceived must be by making some interruption in the circuit.” Cavendish built a battery of Leyden jars and noted that the distance to which the spark flew was not so much a function of the number or size of the jars, but of the force with which they were electrified.57 Cavendish went on to construct some artificial models of the torpedo based on the anatomy and electricity of the fish described by Walsh. After several intents he settled on one where the body was built of “several pieces of thick leather such as used for the soles of shoes”. The surface of this body was covered with thin plates of pewter intended to represent the upper and lower surface of the electric organs. The pewter plates were provided with glass-insulated wires, which could be connected to a battery. The whole part was covered with a piece of sheep’s leather, and the construction kept in water salty as seawater. Cavendish discharged different numbers of Leyden jars through his artificial torpedo and placing his hands on or near it he found that the sensations agreed with descriptions of the shock of the real torpedo, done under different conditions (in water, totally or partially, or in air). Cavendish concluded: “On the whole, I think, there seems nothing in the phenomena of the torpedo at all incompatible with electricity, but to make a complete simulation of them would require a battery much larger than mine”.57 A year later, Nicholson published a paper in which he tried to explain with the help of an electrophorus, the mechanism by which the torpedo and other fish communicated an electric shock.31 According to his description, an electrophorus consisted of a flat metallic plate with an insulating handle, and another separate plate of non-conducting matter, coated with a metal beneath, and placed with its uncoated plate uppermost. When this uncoated plate was electrified by friction or other means, and the metal plate placed on top of it, the latter was found to give a small spark to the finger, which was of the of the same nature (positive or negative) as the electricity of non-conducting surface. When the plate was lifted by its insulating arm, it emitted a spark much stronger, and of the opposite kind to that of the non-conducting plate (the electrophorus could be thought of as a Leyden jar whose capacity diminishes as its shield is raised). Nicholson found that two square inches of mica (an excellent non-conductor) about 1/100 in thick, coated with tin foil, required one turn of a small cylinder to discharge through 1/10 of an inch, and that one turn of the same cylinder charged a simple conductor of about six square feet surface, so as to give a spark about 9 inches long.31 Nicholson went on to compare the structure of the electrophorus to that of the electric organs of the torpedo, given by Hunter in 1773.55 According to Hunter, the electric organ of the torpedo was built of a number (470 to 1182) of columns varying in length from 0.25 to 1.5 inches, and diameter 0.2 inch, and composed of films parallel to the base. The distance between each partition was 1/150 of an inch. Nicholson estimated that if these films were charged with electricity and be 1/300 of an inch thick, the two organs of the torpedo would have an area of 4,500 square inches. His own experiments showed that the laminæ or plates of Muscovy talk (mica), 0.01 in thick, had twelve times the capacity of the glass of a jar of 421 square inches. From this information he deduced that the two organs of the torpedo must have a capacity equivalent to that of a jar of 162 000 square inches.31 Nicholson remarked that the information available about the torpedo did not allow establishing how the charge was actually produced, maintained, and communicated. Nevertheless, it appeared to him, from the observation of the high electric state which mica naturally possessed, and from the countless shock the electrophorus was capable of giving by a simple change of arrangement, that it would be possible to “build a machine capable of giving numberless shocks of pleasure, and of retaining its power for months, years, or to an extent of time of which the limits could be determined only by experiment.” He wrote: “he would not describe the possible constructions he had thought about, but show that the dimensions of the organs of the torpedo were such…to produce the effects observed.” His results indicated that the laminæ of new mica, which had never been excited or electrified, were naturally in strong, opposite electric state, counterbalancing each other, and when separated in the dark, they gave flashes at least 1/10 of an inch long, a value 1875 times the intensity of the torpedo electricity. On the basis of this observation, he assumed that to produce the intensity of the torpedo it was enough to build one or more columns of mica, or other thin


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electric plates 1/300 of an inch thick, and in number equal to the surface of the electric organs of the torpedo, These plates were coated on the outside and ordered in such a way that they touched each other by pairs only (in opposite states); one common conductor communicated with the upper plate of every pair, and another in the same manner with the lower. A separation of the pairs to the distance of only 1/12750 inch was enough to produce the same intensity as the torpedo. According to Nicholson, in order for the torpedo to operate like this machine, required that (a) the membranes were non-conducting and separated by a conducting fluid; (b) that these membranes functioned as electrophorus; and (c) the white reticular matter between the columns consisted of conductors leading to the opposite surfaces, and these conductors were kept separated by a layer of non-conducting matter; or by their movement in a non-conducting fluid.31 Miscellaneous Light, candles, and tallow In a paper published in 1797, Nicholson reviewed the information that was available about the production of light by combustion in lamps or candles, the possibility of replacing wax by tallow, and the experiments he had done on the subject.35 In the introduction to this memoir he made some remarks regarding the importance of light for the purposes of human life quality: “Immediately after the needs for food, lodging, and clothing, was the need of artificial light during the absence of sun; although we could exist without light, a large part of our lives would condemned to a state little above in efficiency from that of animals that surrounded us, and that most probable, human morals would become degraded. The only means of producing light were by combustion of certain masses of fuel in the solid state; the most useful method was the one based on burning fat, of animal or vegetable origin, by means of a wick, the proper instruments being lamps or candles. In the lamp, the oil had to be one that retained its fluidity at ordinary temperatures and pressures. The candle was made of oil or other material, which only fused at a higher temperature”.35 Nicholson went on to describe the different procedures for measuring the relative intensity of light, particularly those proposed by Pierre Bouger (1698-1758), Joseph Priestley (1733-1804), and Benjamin Thompson (Count Rumford, 1753-1814). He indicated that in 1785 he had followed these procedures and had become convinced that they were able to determine the degree of illumination within 1/8th or 1/9th part of the real one. These experiments had led to some additional consequences, for example, the light of a candle, which was exceedingly brilliant when first lit, rapidly diminished to one-half or less before the uneasiness of the eye led us to extinguish it. Hence, if candles could be made so as not require extinction (that is, burn to the end), the average amount of light produced by the same amount of fuel, would be more than doubled. Since the cost and duration of candles and the consumption of oil in lamps was easily determined, it was possible to find if more or less light was obtained at the same expense during a given time, by burning a number of small candles instead of a thicker one. Nicholson wrote that his experiments showed that illumination by means of candles was an expensive and wasteful procedure.35 The most obvious inconvenience of oil lamps in general, arose from the fluidity of the combustible material, which required a vessel adapted to contain it, even the best lamps available, lost oil by spillage.35 A remarkable detail distinguished the combustion process of candle from that of a lamp. In the lamp, the tallow, which had not melted, served as a cup or cavity to hold that portion of the melted tallow, which was ready to flow into the lighted part of the wick. In the candle, the combustion was not confined to a certain position of the wick; the surrounding cup descended by a continuous flow, along the whole length of the candle, and thus the need for frequent extinction. This inconvenience highlighted the importance of the freezing point of the fat. It was well known that the flame brilliancy was highly dependent on the diameter of the wick being as small as possible. The wick of a tallow candle had to be thicker in proportion to the greater fusibility of the material, which would otherwise melt the sides of the cup and run over in streams. The resulting flame was then yellow, smoky, and obscure. Waxes did not provide a flame as brilliant as that of tallow, but their smaller fusibility allowed making the wick smaller and thus obtain a clear perfect flame. Unfortunately, the higher flexibility of the wick cause it to turn on one side and come in contact with the external air, which completely burned the end of the wick to which ashes, and thus play the role of an extinguisher. These observations led Nicholson to conclude that the task of making tallow candles similar to those of wax did not depend on the combustibility of the respective materials, but on the mechanical advantage of the cup.35 Nicholson tried unsuccessfully to increase the fusion of tallow by mixing it with a variety of other materials, and observing the burning process. First of all, he melted tallow in small silver vessel el and noticed that solid tallow sunk in the fluid and dissolved without any remarkable appearance. He then added tears of sandarc resin (a resin secreted by Tetraclinis articulata, a cypress-like tree) and noted that although they did not dissolve in melted tallow, it swelled up, emitted fumes, became brown, and became crisp, but did not improve the burning properties of tallow. Similar results were obtained with shellac, styrax resin (benzoin), common resin (rosin), camphor, potassium sulfate, nitrate, and tartrate, sugar, borax, potassium monoxalate, and magnesium oxide. Since chemists believed that that the hardness of wax was due to the oxygen it contained, Nicholson suggested that other materials to be tested were vinegar, formic acid, galls, the tanning principle (gallic acid), vegetable gluten, birdlime, the serous and gelatinous animal matter, etc.35


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Water simmering Nicholson wrote that it was remarkable that in spite all the work carried on regarding the properties of water in all its states, the cause of its simmering was still unclear. He had believed that it was the consequence of the rapid escape of the air enclosed in the water, until a friend told him that the real explanation was another: when a metallic vessel containing water was put over fire, the vessel gradually became lined with bubbles, which became detached and rose to the surface, so that the bottom became clear again, and soon afterwards, a sharp metallic rattling and increasing noise was heard, resembling the pouring of small shot into the vessel. During this stage the liquid remained quiet and transparent; when the noise reached its highest level, boiling begun suddenly while the simmering noise ceased completely. Observation of this fact led Nicholson to assume that the noise of simmering arose from the collapse of steam bubbles formed at the bottom of the vessel (today: cavitation), and condensed almost instantly during their ascent in the fluid not yet heated to its boiling point.34 To test his hypothesis, Nicholson carried on four experiments during which he heated water in glass or copper vessels of different shapes. In the first experiment, he suspended a small glass retort so that its neck was at an angle of about 20 °. The vessel and most of its neck was filled with water and then heated from beneath with an alcohol lamp. Air was soon seen to separate from the water turning it dusty. After three minutes the inner surface became clear, the peculiar noise of simmering was heard, and bubbles were seen suddenly appearing and collapsing; the retort itself became agitated while the surface of the water rose and fall. The bubbles were pointed at the top, resembling small flames appearing and disappearing at different parts of the surface. In the following minute the bubbles became large and collapsed at greater heights, until they begun escaping from the liquid, as steam. This was the instant of ebullition, the noise of simmering disappeared and was replaced by that of boiling. Since the effect appeared to be caused by the upper water being colder than that near the bottom. Nicholson carried the next experiment in a glass vessel having double the diameter of the one used in the previous experiment, and a straight vertical neck of about 20 cm length. Heating was also conducted with an alcohol lamp located near the bottom of the vessel. The course of the events was more or less similar than the one before. After 40 min bubbles begun to rise singly and very little dustiness was seen. At 58 min the noise of simmering began and the collapsing bubbles were plentiful and distinct. Little firearms rose from particular points and some large bubbles were seen to ascent clearly from the bottom and collapse in the figure above. Shortly thereafter, the bubbles reached the top of the water without collapsing, and the noise of simmering ceased. In the next experiment, another one made of copper, and having the same diameter replaced the glass vessel. After five minutes the inside surface was dusty from air bubbles arising immediately over the flame; at six minutes the bubbles of gas or air were detached and rose, and steam became visible from the surface of the water. At eight minutes the inside surface became coated with large bubbles of air, and little afterwards, the bottom was clear of bubbles, the noise of simmering began, and slowly increased in level, while the bubbles increased in size. When the temperature reached 185 0F (85 0C) some of the bubbles broke at the surface and the noise of simmering became weaker. At 204 0F (95.6 0C) the water boiled and the noise of boiling replaced that of simmering. The last experiment was a continuation of the previous one. The water was left to cool to 1700F (76.70C) and the lamp was lit again. At 180 0F (82.2 0C) simmering began, but not until the steam bubbles were very large. At 204 0F (95.6 0C) the bubbles rose through the fluid and boiling took place by fountains of bubbles arising from particular point. The simmering in this experiment was weaker than in the previous one.34 Nicholson concluded that his experiments clearly showed that the noise of simmering was caused by the condensation of steam bubbles in their ascent through the cold water above.34 Optics In 1786, Francis Hopkinson (1737-1791) published a copy of a letter he had sent the year before to his friend David Rittenhouse (1732-1796), the famous American astronomer, describing an optical phenomenon he had observed, and requesting an explanation for the same.58 Hopkinson had held a silk handkerchief tight between his hands and looked a street lamp located about 30 meters away. To his surprise he had noted that moving the handkerchief to the right and left, the dark bars of the silk threads did not seem to move at all, and remained at the same position before his eyes. In his answer, Rittenhouse had explained that the appearance of certain luminous points regularly arranged in a square array of straight lines crossing each other at a right angle, did not consist of an image of the threads of the handkerchief, because a distinct image of any object placed close to the eye could not be formed by parallel rays, or such as issued from a distant luminous point, because all such rays passing through the pupil, would be collected at the bottom of the eye, and there form an image of the luminous point. What Hopkinson actually saw where images of the lamp, formed by the inflection of light passing near the threads. In order to prove his hypothesis, Rittenhouse built several apparatuses having a different number of parallel hairs, and looked through them at a small opening in the window shutter of a dark room, holding the hairs parallel to the slit. In every case he saw a number of parallel lines almost equal in brightness, and on each side a different number of lines, fainter and more colored. In addition, he noticed that a considerable portion of the beam light passed between the hairs, without being at all bent out of its first course. The remaining rays bent a little, in an amount depending on their color; for


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example, the red rays bent more than the blue ones; contrary to what happened in refraction, when light passed obliquely through the common surface of two different media.58 In 1797, Nicholson wrote that Rittenhouse’s explanation was an incomplete explanation of the phenomenon. He repeated the original experiments, this time looking at a street lamp through a piece of muslin containing 300 threads in the inch. He noted that instead of one, there were nine spots of light, four of them located in the corner of a square, one in the center, and four located in the middle point of the sides of the square. Examination of these spots with an achromatic perspective magnifying fourteen times, showed that they were true images of the flame of the lamp. The central spot was perfect and all the others colored. No changes were observed if the cloth was applied close to the object glass, of at a larger distance.32 According to his results, Nicholson concluded that (a) the middle flame was formed of all the pencils of light that passed through the central parts of the holes in the cloth, without deflection; (b) the four flames in the middle of the sides were formed by the pencils of light inflected towards the short threads bounding each square hole in the cloth, assisted by the deflective power of the opposite threads, respectively; (c) the central flames were formed by the combined action of the two threads contiguous to the angles of every hole; and (c) since the images were produced by an equal number of classes of pencils parallel to each other, they were not be influenced by any motion of the cloth, parallel or perpendicular to its own plane before the object glass, because they came to the objective lens under the same conditions of parallelism.32 Nicholson remarked that replacing the above cloth by another one made of brass wire, containing fifty-five threads per inch, resulted in the appearance of additional lights: Besides the square containing the nine flames described above, there were other flames, much fainter, more colored and elongated, and not arranged radially but in lines forming prolongations of the sides of the middle square, parallel to the thread of the cloth.32 In another paper about optical phenomena, Nicholson reported his experiments and results on the range of colors observed depending on the relative position of two plain glasses.33 In the first part of his memoir he described the laws derived by Isaac Newton (1642-1727) regarding the ranges of colors, which were produced by the reflection and transmission of light through thin transparent plates.59 It was well known that when a convex lens was put on a plain glass, colored circles surrounded the place of contact, and that the dimensions of these circles varied with the relative position of both glasses. According to Newton, the light rays possessed a property by which in certain equidistant points of their length, they were capable of entering transparent bodies and in other intermediate points, and they were reflected. Hence, if a light ray passed through the first surface of a medium, it would be either transmitted or reflected at the second surface, according if the distance coincided with a point of transmission or reflection. In other words, the interval governed this effect not because of its magnitude, but of the precise number of measures, or as Newton called them, fits of transmission or reflection it contains.59 Nicholson mentioned that experiments made by other scientists, such as the Abbé Guillaume Mazéas (1712-1776), Pieter van Muschenbroeck (1682-1761) and Giovanni Bautista Beccaria (1716-1781), appeared to prove that the reflection and transmission of light in the same medium was governed by additional factors to the distance between the surfaces. Mazéas noticed that rubbing two glasses together caused the colors to appear at the same time that adhesion took place; Muschenbroeck found that lenses of long focus did not provide colors after being laid by for same time, unless they were washed and wiped; and Beccaria reported that the colors could also be produced by superimposing an electric charge on the external surfaces of two plates, which caused their adherence. All this information led Nicholson to perform additional experimentation on the subject.33 For this purpose, he cut two pieces of a glass, 12/100ths of an inch (3.048 mm) thick, which had been carefully ground by an optician so that its sides were truly parallel to each other. A piece 3.2 in long and 2.4 in wide was laid upon another larger piece, both previously wiped. Nicholson observed the appearance of faint colors, in six or seven rows, as long as the glasses could slide one on top of the other. Pressure did not cause a change in position but led production of brighter colors, which crossed the previous ones but did not affect them. When a metallic place was now put under the lower glass and electricity communicated to the upper one, the brighter colors appeared and the adhesion of the glasses was increased. Nicholson remarked that similar effects took place when making observations with an artificial horizon and a sextant constructed by Edward Troughton (1753-1835). A series of colors were noticed in the horizon glass when the position of the zero was to be ascertained, these colors appeared both in the silvered and the clear part. Nicholson now repeated the first experiments changing as much as possible, the distance between the to glasses. He found that as long as he maintained the parallelism, the colors appeared even at a distance of 1.20 m. He was convinced that the same phenomenon would take place at even largest distance.33 BIBLIOGRAPHIC REFERENCES

1. Anonymous. Memoir of William Nicholson, Esq. European Mag. London Rev. 1812: 62; 83-87. 2. Anonymous. Account of Mr. Wm. Nicholson. New Monthly Magazine. 1816: 4; 76-7. 3. Golinski J. Nicholson, William (1753–1815). Oxford Dictionary of National Biography, Oxford University

Press. 2004.


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4. Nicholson W. An Introduction to Natural Philosophy. London: Johnson; 1782. Two volumes. 5. Rowning J. A Compendious System of Natural Philosophy. London: Harding; 1744 6. Nicholson W. Ralph’s Survey of the Public Buildings of London. London; 1782. 7. Benyowsky M A. Memoirs and Travels of Mauritius Augustus Count de Benyowsky, Magnate of the

Kingdom of Hungary and Poland, One of the Chiefs of the Confederation of Poland &c., &c; translated from the French by William Nicholson; London: Robinson; 1790.

8. Maistre de la Tour. The History of Ayder Ali Khan, Nabob-Bahader; translated from the French by William Nicholson; London: Johnson; 1784.

9. Nicholson W. The Navigator's Assistant, Containing the Theory and Practice of Navigation, with all the Tables Requisite for Determining a Ship's Place at Sea, Longman, London, 1784.

10. Nicholson W. Abstract of the Arts Relative to the Exportation of Wool, London, 1786. 11. Küttner C. G. Nicholson W. New and Complete Dictionary of the German Language of Englishmen,

Schwickert, Leipzig, 1805; 3 vols. 12. Kirwan R. Essay on Phlogiston and the Constitution of Acids, London, 1787; translated into French as Essai

sur le Phlogistique et sur la Constitution des Acides by Guyton de Morveau L B. Lavoisier A L. Laplace P S. Monge G. Berthollet C. Fourcroy, A F. Paris, 1788; translated in to English by William Nicholson, Davis, London, 1787.

13. Pajot des Charmes C. The Art of Bleaching Piece-Goods, Cottons, and Threads, of Every Description; translated from the French by William Nicholson, Robinson, London, 1799.

14. Fourcroy A F. Synoptic Tables of Chemistry; translated from the French by William Nicholson; Cadell, London, 1801.

15. Fourcroy A F. Système des Connaissances Chimiques, Badouin, Paris, 1801; translated from the French by William Nicholson; Cadell, London, 1801.

16. Chaptal J A C. Elements of Chemistry, translated from the French by William Nicholson; Robinson, London, 1791.

17. Nicholson W. The First Principles of Chemistry, Robinson, London, 1790. 18. Nicholson W. A Dictionary of Chemistry, Robinson, London, 1795. 19. Nicholson W. The British Encyclopedia or, Dictionary of Arts and Sciences, Comprising an Accurate and

Popular View of the Present Improved State of Human Knowledge, Lowry and Scott, London, 1809. 20. Ure A. Nicholson W. A Dictionary of Chemistry and Mineralogy, with their Applications, Tegg, London,

1821. 21. Nicholson W. A Description of an Instrument which, by the Turning of a Winch, Produces the Two States of

Electricity Without Friction or Communication with the Earth, in a Letter from Mr. William Nicholson to Sir. Joseph Banks. Phil Trans. 1788: 78; 403-407.

22. Nicholson W. Description of an Instrument which Renders the Electricity of the Atmosphere and other Weak Charges very Perceptible, without the Possibility of and Equivocal Result. Nicholson J. 1797: 1; 16-18.

23. Bennett A. An Account of a Doubler of Electricity or a Machine by which the Least Conceivable Quantity if Positive or Negative Electricity may be Continually Doubled, till it becomes Perceptible by Common Electrometers, or Visible by Sparks. Phil Trans. 1787: 77; 288-296.

24. De Queiroz A C M. Doublers of Electricity. Phys Educ. 2007: 157-162. 25. Nicholson W. Account of the New Electrical or Galvanic Apparatus of Sig. Alex. Volta, and Experiments

Performed with the Same. Nicholson J. 1801: 4; 179-187. 26. Nicholson W. Experiments and Observations on Electricity Phil Trans Roy Soc. 1789: 79; 265-288. 27. Nicholson W. Description of an Improved Electrometer, in which the Sensibility of the Gold Leaf is

Considerably Augmented, and the Intensities are Distinguished by Numerical Graduation. Nicholson J. 1797: 1; 270-271.

28. Nicholson W. Note Respecting the Instruments by which the Two Kinds of Electricity are Distinguished, or their Direction Ascertained. Nicholson J. 1802: 3; 121-123.

29. Nicholson J. Electrical Battery of Talc. Nicholson J. 1803: 5; 216-217. 30. Nicholson J. Some Facts and Speculations on the Luminous Phenomena of Electricity. Nicholson J. 1806:

13; 87-88. 31. Nicholson W. Observations on the Electrophore, Tending to Explain the Means by which the Torpedo and

other Fish Communicate the Electric Shock. Nicholson J. 1797: 1; 355-359. 32. Nicholson W. A Remarkable Effect of the Inflection of Light Passing through Wire Cloth, not Clearly

Explained. Nicholson J. 1797: 1; 13-16. 33. Nicholson W. Experiments and Remarks on Certain Ranges of Colours hitherto Unobserved, which are

Produced by the Relative Position of Plain Glasses, with Regard to each other. Nicholson J. 1799: 2; 312-315.


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34. Nicholson W. On the Peculiar Noise Emitted by Water before it Acquires the Temperature of Boiling, which is Commonly Denoted by the Word Simmering. Nicholson J. 1805: 1; 216-220.

35. Nicholson W. Observations and Experiments on the Light, Expense and Construction of Lamps and Candles, and the Probability of Rendering Tallow a Substitute for Wax. Nicholson J. 1797: 1; 67-73.

36. Nicholson, W., On the Mechanical Projects for Affording a Perpetual Motion. Nicholson J. 1797: 1; 375-380.

37. Nicholson W. Concerning the Perpetual Motions, which are Produced in Machines by the Rise and Fall of the Barometer or the Thermal Variations in the Dimensions of Bodies. Nicholson J. 1800: 3; 126-128, 172-175.

38. Nicholson W. A Description of a New Instrument for Measuring the Specific Gravity of Bodies. Mem Phil Soc Manchester. 1789: 2; 370-380.

39. Nicholson W. The Principles and Illustration of an Advantageous Method of Arranging the Differences of Logarithms, on Lines Graduated for the Purpose of Calculation. Phil Trans. 1787: 77; 246-252.

40. Nicholson W. A Machine or Instrument on a New Construction for the Purpose of Printing on Paper, Linen, Cotton Woolen and other Articles in a more Neat, Cheap, and Accurate Manner than is Effected by the Machines now in Use, British Patent #1748, April 29, 1790.

41. Nicholson W. A Method of Disposing Gunter’s Line of Numbers, by which the Divisions are Enlarged, and other Advantages Obtained. Nicholson J. 1797: 1; 372-375.

42. Nicholson W. On the Mechanism by which the Mariner’s Compass is Suspended. Nicholson J. 1797: 1; 426-429.

43. Nicholson W. Description of a New Instrument for Drawing Equidistant and other Parallel Lines with Great Accuracy and Expedition. Nicholson J. 1799: 1; 429-431.

44. Nicholson W. Device for Manufacturing Files by Cutting Grooves in Metal, British Patent #2641, 1802. 45. Nicholson W. Steam Blasting Apparatus, British Patent #2990, April 29, 1806. 46. Nicholson W. Suspension System for Carriages, British Patent #2641, 1812. 47. Varley R. Specification of the Patent Granted to Mr. Richard Varley of Domside, near Bolton-le Moors, in

the Country of Lancashire, for his Invention of a New Perpetual Moving Power. The Repertory of Arts and Manufactures. 1799: 10; 9-11.

48. New Patents, The Monthly Magazine, and British Register for 1797. 1798; 4; 58. 49. Nicholson W. Note to Correspondents. Nicholson J. 1797: 1; 334. 50. Anonymous. Hist Acad Roy Sci. 1775: 65-66. 51. Wisniak, J., Conservation of Energy - Readings on the Origins of the First Law of Thermodynamics. Parts I,

II, Educ quím. 2008: 19; 159-171, 216-225. 52. Volta, A., On the Electricity Excited by the Mere Contact of Conducting Substances of Different Kinds. Phil

Trans. 1800: 90; 403-431. 53. Anonymous. Experiments on Galvanic Electricity by Messrs. Nicholson, Carlisle, Cruickshank, etc. Phil

Mag. 1800: 7; 337-347. 54. Walsh J. Seignette S. On the Electric Property of the Torpedo, in a Letter of John Walsh to Benjamin

Franklin. Phil Trans. 1773: 63; 461-477. 55. Hunter J. Anatomical Observations on the Torpedo. Phil Trans. 1773: 63; 481-488. 56. Williamson H. Experiments and Observations on the Gyumnotus Electricus, or Electrical Eel. Phil Trans.

1775: 65; 94-101. 57. Cavendish H. An Account of Some Attempts to Imitate the Effects the Torpedo by Electricity Part I. Phil

Trans. 1776: 66; 192-225. 58. Hopkinson F. An Optical Problem Proposed by Mr. Hopkinson and Solved by Mr. Rittenhouse. Trans Am

Phil Soc. 1786: 2; 201-206. 59. Newton I. Opticks, Smith and Watford, London, 1704; reprinted by Dover Publications, New York, 1952.

determination of d003 by capillary gas...

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