Isaac Newton
Sir Isaac Newton was an English mathematician, astronomer and author, recognised as one of the most influential scientists of all time, a key figure in the scientific revolution. His book Philosophiæ Naturalis Principia Mathematica, first published in 1687, laid the foundations of classical mechanics. Newton made seminal contributions to optics, shares credit with Gottfried Wilhelm Leibniz for developing the infinitesimal calculus. In Principia, Newton formulated the laws of motion and universal gravitation that formed the dominant scientific viewpoint until it was superseded by the theory of relativity. Newton used his mathematical description of gravity to prove Kepler's laws of planetary motion, account for tides, the trajectories of comets, the precession of the equinoxes and other phenomena, eradicating doubt about the Solar System's heliocentricity, he demonstrated that the motion of objects on Earth and celestial bodies could be accounted for by the same principles. Newton's inference that the Earth is an oblate spheroid was confirmed by the geodetic measurements of Maupertuis, La Condamine, others, convincing most European scientists of the superiority of Newtonian mechanics over earlier systems.
Newton built the first practical reflecting telescope and developed a sophisticated theory of colour based on the observation that a prism separates white light into the colours of the visible spectrum. His work on light was collected in his influential book Opticks, published in 1704, he formulated an empirical law of cooling, made the first theoretical calculation of the speed of sound, introduced the notion of a Newtonian fluid. In addition to his work on calculus, as a mathematician Newton contributed to the study of power series, generalised the binomial theorem to non-integer exponents, developed a method for approximating the roots of a function, classified most of the cubic plane curves. Newton was a fellow of Trinity College and the second Lucasian Professor of Mathematics at the University of Cambridge, he was a devout but unorthodox Christian who rejected the doctrine of the Trinity. Unusually for a member of the Cambridge faculty of the day, he refused to take holy orders in the Church of England.
Beyond his work on the mathematical sciences, Newton dedicated much of his time to the study of alchemy and biblical chronology, but most of his work in those areas remained unpublished until long after his death. Politically and tied to the Whig party, Newton served two brief terms as Member of Parliament for the University of Cambridge, in 1689–90 and 1701–02, he was knighted by Queen Anne in 1705 and spent the last three decades of his life in London, serving as Warden and Master of the Royal Mint, as well as president of the Royal Society. Isaac Newton was born on Christmas Day, 25 December 1642 "an hour or two after midnight", at Woolsthorpe Manor in Woolsthorpe-by-Colsterworth, a hamlet in the county of Lincolnshire, his father named Isaac Newton, had died three months before. Born prematurely, Newton was a small child; when Newton was three, his mother remarried and went to live with her new husband, the Reverend Barnabas Smith, leaving her son in the care of his maternal grandmother, Margery Ayscough.
Newton disliked his stepfather and maintained some enmity towards his mother for marrying him, as revealed by this entry in a list of sins committed up to the age of 19: "Threatening my father and mother Smith to burn them and the house over them." Newton's mother had three children from her second marriage. From the age of about twelve until he was seventeen, Newton was educated at The King's School, which taught Latin and Greek and imparted a significant foundation of mathematics, he was removed from school, returned to Woolsthorpe-by-Colsterworth by October 1659. His mother, widowed for the second time, attempted to make him an occupation he hated. Henry Stokes, master at The King's School, persuaded his mother to send him back to school. Motivated by a desire for revenge against a schoolyard bully, he became the top-ranked student, distinguishing himself by building sundials and models of windmills. In June 1661, he was admitted to Trinity College, Cambridge, on the recommendation of his uncle Rev William Ayscough, who had studied there.
He started as a subsizar—paying his way by performing valet's duties—until he was awarded a scholarship in 1664, guaranteeing him four more years until he could get his MA. At that time, the college's teachings were based on those of Aristotle, whom Newton supplemented with modern philosophers such as Descartes, astronomers such as Galileo and Thomas Street, through whom he learned of Kepler's work, he set down in his notebook a series of "Quaestiones" about mechanical philosophy. In 1665, he discovered the generalised binomial theorem and began to develop a mathematical theory that became calculus. Soon after Newton had obtained his BA degree in August 1665, the university temporarily closed as a precaution against the Great Plague. Although he had been undistinguished as a Cambridge student, Newton's private studies at his home in Woolsthorpe over the subsequent two years saw the development of his theories on calculus and the law of gravitation. In April 1667, he returned in October was elected as a fellow of Trinity.
Fellows were required to become ordained priests, although this was no
Solar wind
The solar wind is a stream of charged particles released from the upper atmosphere of the Sun, called the corona. This plasma consists of electrons and alpha particles with kinetic energy between 0.5 and 10 keV. Embedded within the solar-wind plasma is the interplanetary magnetic field; the solar wind varies in density and speed over time and over solar latitude and longitude. Its particles can escape the Sun's gravity because of their high energy resulting from the high temperature of the corona, which in turn is a result of the coronal magnetic field. At a distance of more than a few solar radii from the Sun, the solar wind is supersonic and reaches speeds of 250 to 750 kilometers per second; the flow of the solar wind is no longer supersonic at the termination shock. The Voyager 2 spacecraft crossed the shock more than five times between 30 August and 10 December 2007. Voyager 2 crossed the shock about a billion kilometers closer to the Sun than the 13.5-billion-kilometer distance where Voyager 1 came upon the termination shock.
The spacecraft moved outward through the termination shock into the heliosheath and onward toward the interstellar medium. Other related phenomena include the aurora, the plasma tails of comets that always point away from the Sun, geomagnetic storms that can change the direction of magnetic field lines; the existence of particles flowing outward from the Sun to the Earth was first suggested by British astronomer Richard C. Carrington. In 1859, Carrington and Richard Hodgson independently made the first observation of what would be called a solar flare; this is a sudden, localised increase in brightness on the solar disc, now known to occur in conjunction with an episodic ejection of material and magnetic flux from the Sun's atmosphere, known as a coronal mass ejection. On the following day, a geomagnetic storm was observed, Carrington suspected that there might be a connection, now attributed to the arrival of the coronal mass ejection in near-Earth space and its subsequent interaction with the Earth's magnetosphere.
George FitzGerald suggested that matter was being accelerated away from the Sun and was reaching the Earth after several days. In 1910 British astrophysicist Arthur Eddington suggested the existence of the solar wind, without naming it, in a footnote to an article on Comet Morehouse; the idea never caught on though Eddington had made a similar suggestion at a Royal Institution address the previous year. In the latter case, he postulated that the ejected material consisted of electrons while in his study of Comet Morehouse he supposed them to be ions; the first person to suggest that the ejected material consisted of both ions and electrons was Kristian Birkeland. His geomagnetic surveys showed; as these displays and other geomagnetic activity were being produced by particles from the Sun, he concluded that the Earth was being continually bombarded by "rays of electric corpuscles emitted by the Sun". In 1916, Birkeland proposed that, "From a physical point of view it is most probable that solar rays are neither negative nor positive rays, but of both kinds".
In other words, the solar wind consists of positive ions. Three years in 1919, Frederick Lindemann suggested that particles of both polarities, protons as well as electrons, come from the Sun. Around the 1930s, scientists had determined that the temperature of the solar corona must be a million degrees Celsius because of the way it stood out into space. Spectroscopic work confirmed this extraordinary temperature. In the mid-1950s Sydney Chapman calculated the properties of a gas at such a temperature and determined it was such a superb conductor of heat that it must extend way out into space, beyond the orbit of Earth. In the 1950s, Ludwig Biermann became interested in the fact that no matter whether a comet is headed towards or away from the Sun, its tail always points away from the Sun. Biermann postulated that this happens because the Sun emits a steady stream of particles that pushes the comet's tail away. Wilfried Schröder claimed that Paul Ahnert was the first to relate solar wind to comet tail direction based on observations of the comet Whipple-Fedke.
Eugene Parker realised heat flowing from the Sun in Chapman's model and the comet tail blowing away from the Sun in Biermann's hypothesis had to be the result of the same phenomenon, which he termed the "solar wind". In 1957, Parker showed though the Sun's corona is attracted by solar gravity, it is such a good heat conductor that it is still hot at large distances. Since gravity weakens as distance from the Sun increases, the outer coronal atmosphere escapes supersonically into interstellar space. Furthermore, Parker was the first person to notice that the weakening effect of the gravity has the same effect on hydrodynamic flow as a de Laval nozzle: it incites a transition from subsonic to supersonic flow. Opposition to Parker's hypothesis on the solar wind was strong; the paper he submitted to The Astrophysical Journal in 1958 was rejected by two reviewers. It was saved by the editor Subrahmanyan Chandrasekhar. In January 1959, the Soviet spacecraft Luna 1 first directly observed the solar wind and measured its strength, using hemispherical ion traps.
The discovery, made by Konstantin Gringauz, was verified by Luna 2, Luna 3 and by the more distant measurements of Venera 1. Three years a similar measurement was performed by Neugebauer and collaborators using the Mariner 2 spacecraft. In the late 1990s, the Ultraviolet Coronal Spectrometer instrument on board the SOHO spacecraft observed the acceleration region of the fast s
Tonne
The tonne referred to as the metric ton in the United States and Canada, is a non-SI metric unit of mass equal to 1,000 kilograms or one megagram. It is equivalent to 2,204.6 pounds, 1.102 short tons or 0.984 long tons. Although not part of the SI, the tonne is accepted for use with SI units and prefixes by the International Committee for Weights and Measures; the tonne is derived from the weight of 1 cubic metre of pure water. The SI symbol for the tonne is't', adopted at the same time as the unit in 1879, its use is official for the metric ton in the United States, having been adopted by the United States National Institute of Standards and Technology. It is a symbol, not an abbreviation, should not be followed by a period. Use of upper and lower case is significant, use of other letter combinations is not permitted and would lead to ambiguity. For example,'T','MT','Mt','mt' are the SI symbols for the tesla, megatesla and millitonne respectively. If describing TNT equivalent units of energy, this is equivalent to 4.184 petajoules.
In French and most varieties of English, tonne is the correct spelling. It is pronounced the same as ton, but when it is important to clarify that the metric term is meant, rather than short ton, the final "e" can be pronounced, i.e. "tonny". In Australia, it is pronounced. Before metrication in the UK the unit used for most purposes was the Imperial ton of 2,240 pounds avoirdupois or 20 hundredweight, equivalent to 1,016 kg, differing by just 1.6% from the tonne. The UK Weights and Measures Act 1985 explicitly excluded from use for trade certain imperial units, including the ton, unless the item being sold or the weighing equipment being used was weighed or certified prior to 1 December 1980, then only if the buyer was made aware that the weight of the item was measured in imperial units. In the United States metric ton is the name for this unit used and recommended by NIST. Both spellings are acceptable in Canadian usage. Ton and tonne are both derived from a Germanic word in general use in the North Sea area since the Middle Ages to designate a large cask, or tun.
A full tun, standing about a metre high, could weigh a tonne. An English tun of wine weighs a tonne, 954 kg if full of water, a little less for wine; the spelling tonne pre-dates the introduction of the SI in 1960. In the United States, the unit was referred to using the French words millier or tonneau, but these terms are now obsolete; the Imperial and US customary units comparable to the tonne are both spelled ton in English, though they differ in mass. One tonne is equivalent to: Metric/SI: 1 megagram. Equal to 1000000 grams or 1000 kilograms. Megagram, Mg, is the official SI unit. Mg is distinct from milligram. Pounds: Exactly 1000/0.453 592 37 lb, or 2204.622622 lb. US/Short tons: Exactly 1/0.907 184 74 short tons, or 1.102311311 ST. One short ton is 0.90718474 t. Imperial/Long tons: Exactly 1/1.016 046 9088 long tons, or 0.9842065276 LT. One long ton is 1.0160469088 t. For multiples of the tonne, it is more usual to speak of millions of tonnes. Kilotonne and gigatonne are more used for the energy of nuclear explosions and other events in equivalent mass of TNT loosely as approximate figures.
When used in this context, there is little need to distinguish between metric and other tons, the unit is spelt either as ton or tonne with the relevant prefix attached. *The equivalent units columns use the short scale large-number naming system used in most English-language countries, e.g. 1 billion = 1,000 million = 1,000,000,000.†Values in the equivalent short and long tons columns are rounded to five significant figures, see Conversions for exact values.ǂThough non-standard, the symbol "kt" is used for knot, a unit of speed for aircraft and sea-going vessels, should not be confused with kilotonne. A metric ton unit can mean 10 kilograms within metal trading within the US, it traditionally referred to a metric ton of ore containing 1% of metal. The following excerpt from a mining geology textbook describes its usage in the particular case of tungsten: "Tungsten concentrates are traded in metric tonne units (originally designating one tonne of ore containing 1% of WO3, today used to measure WO3 quantities in 10 kg units.
One metric tonne unit of tungsten contains 7.93 kilograms of tungsten." Note that tungsten is known as wolfram and has the atomic symbol W. In the case of uranium, the acronym MTU is sometimes considered to be metric ton of uranium, meaning 1,000 kg. A gigatonne of carbon dioxide equivalent is a unit used by the UN climate change panel, IPCC, to measure the effect of a technolo
Astronomy
Astronomy is a natural science that studies celestial objects and phenomena. It applies mathematics and chemistry in an effort to explain the origin of those objects and phenomena and their evolution. Objects of interest include planets, stars, nebulae and comets. More all phenomena that originate outside Earth's atmosphere are within the purview of astronomy. A related but distinct subject is physical cosmology, the study of the Universe as a whole. Astronomy is one of the oldest of the natural sciences; the early civilizations in recorded history, such as the Babylonians, Indians, Nubians, Chinese and many ancient indigenous peoples of the Americas, performed methodical observations of the night sky. Astronomy has included disciplines as diverse as astrometry, celestial navigation, observational astronomy, the making of calendars, but professional astronomy is now considered to be synonymous with astrophysics. Professional astronomy is split into theoretical branches. Observational astronomy is focused on acquiring data from observations of astronomical objects, analyzed using basic principles of physics.
Theoretical astronomy is oriented toward the development of computer or analytical models to describe astronomical objects and phenomena. The two fields complement each other, with theoretical astronomy seeking to explain observational results and observations being used to confirm theoretical results. Astronomy is one of the few sciences in which amateurs still play an active role in the discovery and observation of transient events. Amateur astronomers have made and contributed to many important astronomical discoveries, such as finding new comets. Astronomy means "law of the stars". Astronomy should not be confused with astrology, the belief system which claims that human affairs are correlated with the positions of celestial objects. Although the two fields share a common origin, they are now distinct. Both of the terms "astronomy" and "astrophysics" may be used to refer to the same subject. Based on strict dictionary definitions, "astronomy" refers to "the study of objects and matter outside the Earth's atmosphere and of their physical and chemical properties," while "astrophysics" refers to the branch of astronomy dealing with "the behavior, physical properties, dynamic processes of celestial objects and phenomena."
In some cases, as in the introduction of the introductory textbook The Physical Universe by Frank Shu, "astronomy" may be used to describe the qualitative study of the subject, whereas "astrophysics" is used to describe the physics-oriented version of the subject. However, since most modern astronomical research deals with subjects related to physics, modern astronomy could be called astrophysics; some fields, such as astrometry, are purely astronomy rather than astrophysics. Various departments in which scientists carry out research on this subject may use "astronomy" and "astrophysics" depending on whether the department is affiliated with a physics department, many professional astronomers have physics rather than astronomy degrees; some titles of the leading scientific journals in this field include The Astronomical Journal, The Astrophysical Journal, Astronomy and Astrophysics. In early historic times, astronomy only consisted of the observation and predictions of the motions of objects visible to the naked eye.
In some locations, early cultures assembled massive artifacts that had some astronomical purpose. In addition to their ceremonial uses, these observatories could be employed to determine the seasons, an important factor in knowing when to plant crops and in understanding the length of the year. Before tools such as the telescope were invented, early study of the stars was conducted using the naked eye; as civilizations developed, most notably in Mesopotamia, Persia, China and Central America, astronomical observatories were assembled and ideas on the nature of the Universe began to develop. Most early astronomy consisted of mapping the positions of the stars and planets, a science now referred to as astrometry. From these observations, early ideas about the motions of the planets were formed, the nature of the Sun and the Earth in the Universe were explored philosophically; the Earth was believed to be the center of the Universe with the Sun, the Moon and the stars rotating around it. This is known as the geocentric model of the Ptolemaic system, named after Ptolemy.
A important early development was the beginning of mathematical and scientific astronomy, which began among the Babylonians, who laid the foundations for the astronomical traditions that developed in many other civilizations. The Babylonians discovered. Following the Babylonians, significant advances in astronomy were made in ancient Greece and the Hellenistic world. Greek astronomy is characterized from the start by seeking a rational, physical explanation for celestial phenomena. In the 3rd century BC, Aristarchus of Samos estimated the size and distance of the Moon and Sun, he proposed a model of the Solar System where the Earth and planets rotated around the Sun, now called the heliocentric model. In the 2nd century BC, Hipparchus discovered precession, calculated the size and distance of the Moon and inven
Cavendish experiment
The Cavendish experiment, performed in 1797–1798 by British scientist Henry Cavendish, was the first experiment to measure the force of gravity between masses in the laboratory and the first to yield accurate values for the gravitational constant. Because of the unit conventions in use, the gravitational constant does not appear explicitly in Cavendish's work. Instead, the result was expressed as the specific gravity of the Earth, or equivalently the mass of the Earth, his experiment gave the first accurate values for these geophysical constants. The experiment was devised sometime before 1783 by geologist John Michell, who constructed a torsion balance apparatus for it. However, Michell died in 1793 without completing the work. After his death the apparatus passed to Francis John Hyde Wollaston and to Henry Cavendish, who rebuilt the apparatus but kept close to Michell's original plan. Cavendish carried out a series of measurements with the equipment and reported his results in the Philosophical Transactions of the Royal Society in 1798.
The apparatus constructed by Cavendish was a torsion balance made of a six-foot wooden rod horizontally suspended from a wire, with two 2-inch diameter 1.61-pound lead spheres, one attached to each end. Two 12-inch 348-pound lead balls were located near the smaller balls, about 9 inches away, held in place with a separate suspension system; the experiment measured the faint gravitational attraction between the small balls and the larger ones. The two large balls were positioned on alternate sides of the horizontal wooden arm of the balance, their mutual attraction to the small balls caused the arm to rotate, twisting the wire supporting the arm. The arm stopped rotating when it reached an angle where the twisting force of the wire balanced the combined gravitational force of attraction between the large and small lead spheres. By measuring the angle of the rod and knowing the twisting force of the wire for a given angle, Cavendish was able to determine the force between the pairs of masses. Since the gravitational force of the Earth on the small ball could be measured directly by weighing it, the ratio of the two forces allowed the density of the Earth to be calculated, using Newton's law of gravitation.
Cavendish found. To find the wire's torsion coefficient, the torque exerted by the wire for a given angle of twist, Cavendish timed the natural oscillation period of the balance rod as it rotated clockwise and counterclockwise against the twisting of the wire; the period was about 20 minutes. The torsion coefficient could be calculated from dimensions of the balance; the rod was never at rest. Cavendish's equipment was remarkably sensitive for its time; the force involved in twisting the torsion balance was small, 1.74×10−7 N, about 1⁄50,000,000 of the weight of the small balls. To prevent air currents and temperature changes from interfering with the measurements, Cavendish placed the entire apparatus in a wooden box about 2 feet thick, 10 feet tall, 10 feet wide, all in a closed shed on his estate. Through two holes in the walls of the shed, Cavendish used telescopes to observe the movement of the torsion balance's horizontal rod; the motion of the rod was only about 0.16 inches. Cavendish was able to measure this small deflection to an accuracy of better than 0.01 inches using vernier scales on the ends of the rod.
The accuracy of Cavendish's result was not exceeded until C. V. Boys's experiment in 1895. In time, Michell's torsion balance became the dominant technique for measuring the gravitational constant and most contemporary measurements still use variations of it. Cavendish's result was the first evidence for a planetary core made of metal; the result of 5.4 g·cm−3 is close to 80% of the density of liquid iron, 80% higher than the density of the Earth's outer crust, suggesting the existence of a dense iron core. The formulation of Newtonian gravity in terms of a gravitational constant did not become standard until long after Cavendish's time. Indeed, one of the first references to G is 75 years after Cavendish's work. Cavendish expressed his result in terms of the density of the Earth. Authors reformulated his results in modern terms. G = g R earth 2 M earth = 3 g 4 π R earth ρ earth After converting to SI units, Cavendish's value for the Earth's density, 5.448 g cm−3, gives G = 6.74×10−11 m3 kg–1 s−2,which differs by only 1% from the 2014 CODATA value of 6.67408×10−11 m3 kg−1 s−2.
For this reason, historians of science have argued that Cavendish did not measure the gravitational constant. Physicists, however use units where the gravitational constant takes a different form; the Gaussian gravitational constant used in space dynamics is a defined constant and the Cavendish experiment can be considered as a measurement of this constant. In Cavendish's time, physicists used the same units for mass and weight, in effect taking g as a standard acceleration. Since Rearth was known, ρearth played the role of an inverse gravitational constant. The
Gaussian gravitational constant
The Gaussian gravitational constant is a parameter used in the orbital mechanics of the solar system. It relates the orbital period to the orbit's semi-major axis and the mass of the orbiting body in Solar masses; the value of k expresses the mean angular velocity of the system of Earth+Moon and the Sun considered as a two body problem, with a value of about 0.986 degrees per day, or about 0.0172 radians per day. As a consequence of Newton's law of gravitation and Kepler's third law, k is directly proportional to the square root of the standard gravitational parameter of the Sun, its value in radians per day follows by setting Earth's semi-major axis to unity, k: = 0.5·-1.5A value of k = 0.01720209895 rad/day was determined by Carl Friedrich Gauss in his 1809 work Theoria Motus Corporum Coelestium in Sectionibus Conicis Solem Ambientum. Gauss' value was introduced as a fixed, defined value by the IAU, which detached it from its immediate representation of the mean angular velocity of the Sun-Earth system.
Instead, the astronomical unit now became a measurable quantity different from unity. This was useful in 20th-century celestial mechanics to prevent the constant adaptation of orbital parameters to updated measured values, but it came at the expense of intuitiveness, as the astronomical unit, ostensibly a unit of length, was now dependent on the measurement of the strength of the gravitational force; the IAU abandoned the defined value of k in 2012 in favour of a defined value of the astronomical unit of 1.495978707×1011 m while the strength of the gravitational force is now to be expressed in the separate standard gravitational parameter GM☉, measured in SI units of m3 s−2. Gauss' constant is derived from the application of Kepler's third law to the system of Earth+Moon and the Sun considered as a two body problem, relating the period of revolution to the major semi-axis of the orbit and the total mass of the orbiting bodies, its numerical value was obtained by setting the major semi-axis and the mass of the Sun to unity and measuring the period in mean solar days: k = 2π / ≈ 0.0172021, where: P ≈ 365.256, M = ≈ 1.00000304, a = 1 by definition.
The value represents the mean angular motion of the Earth-Sun system, in radians per day, equivalent to a value just below one degree. The correction due to the division by the square root of M reflects the fact that the Earth-Moon system is not orbiting the Sun itself, but the center of mass of the system. Isaac Newton himself determined a value of this constant which agreed with Gauss' value to six significant digits. Gauss gave the value as 3548.18761 arc seconds. Since all involved parameters, the orbital period, the Earth-to-Sun mass ratio, the semi-major axis and the length of the mean solar day, are subject to refined measurement, the precise value of the constant would have to be revised over time, but since the constant is involved in determining the orbital parameters of all other bodies in the solar system, it was found to be more convenient to set it to a fixed value, by definition, implying that the value of a would deviate from unity. The fixed value of k = 0.01720209895 was taken to be the one set by Gauss, so that a = 4π2: ≈ 1.
Gauss' 1809 value of the constant was thus used as an authoritative reference value for the orbital mechanics of the solar system for two centuries. From its introduction until 1938 it was considered a measured quantity, from 1938 until 2012 it was used as a defined quantity, with measurement uncertainty delegated to the value of the astronomical unit; the defined value of k was abandoned by the IAU in 2012, the use of k was deprecated, to be replaced by a fixed value of the astronomical unit, the quantity of the standard gravitational parameter GM☉. Gauss himself stated the constant in arc seconds, with nine significant digits, as k = 3548″.18761. In the late 19th century, this value was adopted, converted to radian, by Simon Newcomb, as k = 0.01720209895. and the constant appears in this form in his Tables of the Sun, published in 1898. Newcomb's work was accepted as the best available and his values of the constants were incorporated into a great quantity of astronomical research; because of this, it became difficult to separate the constants from the research.
Hence, after the formation of the International Astronomical Union in 1919 certain constants came to be accepted as "fundamental": defining constants from which all others were derived. In 1938, the VIth General Assembly of the IAU declared, We adopt for the constant of Gauss, the value k = 0.017202098950000 the unit of time is the mean solar day of 1900.0 However, no further effort toward establishing a set of constants was forthcoming until 1950. An IAU symposium on the system of constants was held in Paris in 1963 in response to recent developments in space exploration; the attendees decided at that time to establish a consistent set of constants. Resolution 1 stated that The new system shall be defined by a non-redundant set of fundamental constants, by explicit relations between these and the constants derived from them. Resolution 4 recommended that the working group shall treat the following quantities as fundamental constants (in the s
Henry Cavendish
Henry Cavendish FRS was an English natural philosopher, an important experimental and theoretical chemist and physicist. He is noted for his discovery of hydrogen, which he termed "inflammable air", he described the density of inflammable air, which formed water on combustion, in a 1766 paper, On Factitious Airs. Antoine Lavoisier reproduced Cavendish's experiment and gave the element its name. A notoriously shy man, Cavendish was nonetheless distinguished for great accuracy and precision in his researches into the composition of atmospheric air, the properties of different gases, the synthesis of water, the law governing electrical attraction and repulsion, a mechanical theory of heat, calculations of the density of the Earth, his experiment to measure the density of the Earth has come to be known as the Cavendish experiment. Henry Cavendish was born on 10 October 1731 in Nice, his mother was Lady Anne de Grey, fourth daughter of Henry Grey, 1st Duke of Kent, his father was Lord Charles Cavendish, the third son of William Cavendish, 2nd Duke of Devonshire.
The family traced its lineage across eight centuries to Norman times, was connected to many aristocratic families of Great Britain. Henry's mother died in 1733, three months after the birth of her second son and shortly before Henry's second birthday, leaving Lord Charles Cavendish to bring up his two sons. From the age of 11 Henry attended a private school near London. At the age of 18 he entered the University of Cambridge in St Peter's College, now known as Peterhouse, but left three years on 23 February 1751 without taking a degree, he lived with his father in London, where he soon had his own laboratory. Lord Charles Cavendish spent his life firstly in politics and increasingly in science in the Royal Society of London. In 1758, he took Henry to meetings of the Royal Society and to dinners of the Royal Society Club. In 1760, Henry Cavendish was elected to both these groups, he was assiduous in his attendance after that, he took no part in politics, but followed his father into science, through his researches and his participation in scientific organisations.
He was active in the Council of the Royal Society of London. His interest and expertise in the use of scientific instruments led him to head a committee to review the Royal Society's meteorological instruments and to help assess the instruments of the Royal Greenwich Observatory, his first paper, Factitious Airs, appeared in 1766. Other committees on which he served included the committee of papers, which chose the papers for publication in the Philosophical Transactions of the Royal Society, the committees for the transit of Venus, for the gravitational attraction of mountains, for the scientific instructions for Constantine Phipps's expedition in search of the North Pole and the Northwest Passage. In 1773, Henry joined his father as an elected trustee of the British Museum, to which he devoted a good deal of time and effort. Soon after the Royal Institution of Great Britain was established, Cavendish became a manager and took an active interest in the laboratory, where he observed and helped in Humphry Davy's chemical experiments.
About the time of his father's death, Cavendish began to work with Charles Blagden, an association that helped Blagden enter into London's scientific society. In return, Blagden helped to keep the world at a distance from Cavendish. Cavendish published no books and few papers. Several areas of research, including mechanics and magnetism, feature extensively in his manuscripts, but they scarcely feature in his published work. Cavendish is considered to be one of the so-called pneumatic chemists of the eighteenth and nineteenth centuries, along with, for example, Joseph Priestley, Joseph Black, Daniel Rutherford. Cavendish found that a definite and inflammable gas, which he referred to as "Inflammable Air", was produced by the action of certain acid on certain metals; this gas was, in fact, which Cavendish guessed was proportioned to two in one water. Although others, such as Robert Boyle, had prepared hydrogen gas earlier, Cavendish is given the credit for recognising its elemental nature. By dissolving alkalis in acids, Cavendish made "fixed air", which he collected, along with other gases, in bottles inverted over water or mercury.
He measured their solubility in water and their specific gravity, noted their combustibility. Cavendish was awarded the Royal Society's Copley Medal for this paper. Gas chemistry was of increasing importance in the latter half of the 18th century, became crucial for Frenchman Antoine-Laurent Lavoisier's reform of chemistry known as the chemical revolution. In 1783, Cavendish published a paper on eudiometry, he described a new eudiometer of his invention, with which he achieved the best results to date, using what in other hands had been the inexact method of measuring gases by weighing them. He next published a paper on the production of water by burning inflammable air in "dephlogisticated air", the latter a constituent of atmospheric air. Cavendish concluded that dephlogisticated air was dephlogisticated water and that hydrogen was either pure phlogiston or phlogisticated water, he reported these findings to Joseph Priestley
