Science: A History - Revision history

Robert.adlington: /* Outer Space */

2025-04-09T16:44:21Z

Outer Space

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	* There is no evidence of a special life force, and all of life on Earth, including us, is based on chemical processes. And the four most common elements involved in the chemistry of life are hydrogen, carbon, oxygen and nitrogen. We are made out of exactly the raw materials which are most easily available in the Universe. Earth is not a special place, and life forms based on CHON are likely to be found across the Universe, not just in our Galaxy but in others.		* There is no evidence of a special life force, and all of life on Earth, including us, is based on chemical processes. And the four most common elements involved in the chemistry of life are hydrogen, carbon, oxygen and nitrogen. We are made out of exactly the raw materials which are most easily available in the Universe. Earth is not a special place, and life forms based on CHON are likely to be found across the Universe, not just in our Galaxy but in others.
	* Four and a half centuries after the publication of De Revolutionibus, we are in the situation a that small child who has just learned the rules of the game. We are just beginning to make our first attempts to play the game, with developments such as genetic engineering and artificial intelligence.		* Four and a half centuries after the publication of De Revolutionibus, we are in the situation a that small child who has just learned the rules of the game. We are just beginning to make our first attempts to play the game, with developments such as genetic engineering and artificial intelligence.

			[[Category:Books]]

Rob: /* Outer Space */

2025-04-06T10:47:02Z

Outer Space

Show changes

Rob at 16:13, 5 April 2025

2025-04-05T16:13:29Z

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	** There is no arbitrariness in the arrangement of electrons in atoms and atoms in molecules - the arrangements which are most stable in the atoms and molecules are always the arrangements with the least energy.		** There is no arbitrariness in the arrangement of electrons in atoms and atoms in molecules - the arrangements which are most stable in the atoms and molecules are always the arrangements with the least energy.
	* X-rays are a form of electromagnetic wave, like light but with shorter wavelengths		* X-rays are a form of electromagnetic wave, like light but with shorter wavelengths
	* In a substance like sodium chloride there are no individual molecules (NaCl), but an array of sodium ions and chlorine ions arranged in a geometric pattern		* In a substance like sodium chloride there are no individual molecules (NaCl), but an array of sodium ions and chlorine ions arranged in a geometric pattern.
			* The structure of biomolecules, such as haemoglobin, insulin, and the muscle protein, myoglobin
			* Hydrogen bonds - unlike all other chemically reactive atoms (helium is not chemically reactive), hydrogen has no other electrons in inner shells to help conceal the positive charge on its proton, so some of the positive charge is « visible » to any nearby atoms or molecules. This will attract any nearby atom which has a preponderance of negative charge - such as an oxygen atom in a water molecule, which has gained extra negative charge from its two hydrogen atoms.
			* Astbury showed that globular protein molecules (such as haemoglobin and myoglobin) are made up of long-chain proteins (polypeptide chains) that are folded up to make balls.
			* Pauling laid out in detail the chemical structure of hair, feathers, muscles, silk, horn, and other protein, as well as the alpha-helix structure, as it became known, of the fibres themselves.
			* James Watson (1928-) and Francis Crick (1916-) where influenced by Schrôdinger’s « What is Life? » (1944), which noted that in a code similar to the Morse code but with three symbols, not just dot and dash, used in groups of ten, you could form 88,572 different « letters ».
			* Griffith worked out from the shapes of the molecules that adenine and thymine could fit together, linking up through a pair of hydrogen bonds, while guanine and cytosine could also fit together, linking up through a set of three hydrogen bonds, but that the four bases could not pair up in any other way.
			* The structure of DNA must involve pairs of long-chain molecules, linked together by AG and CT bridges
			* The genetic code is actually written in triplets, with sets of three bases, such as CTA or GGC, representing each of the twenty or so individual amino acids used in the proteins that build and run the body. When proteins are being manufactured by the cell, the relevant part of the DNA helix containing the appropriate gene uncoils, and a string of three-letter codons is copied into a strand of RNA (which of RNA and DNA was first?); this messenger RNA, whose only essential difference to DNA is that it has uracil everywhere DNA has thymine, is then used as a template to assemble a string of amino acids corresponding to the codons, which are linked together to make the required protein. It keeps doing this until no more of that particular protein is required. The DNA has long since coiled up again, and after enough protein has been manufactured the RNA is disassembled and its components reused. Just how the cell knows when and where to do all this remains to be explained, but the principles of the process were clear by the mid 1960s
			* During all the copying of DNA that goes on when cells divide, there must occasionally be mistakes. Bits of DNA get copied twice, or bits get left out, or one base (one letter in the genetic code) gets accidentally replaced by another. None of this matters much in the kind of cell division that produces growth, since all that happens is that a bit of DNA in a single cell (probably not even a bit of DNA that that particular cell uses) has been changed. But when reproductive cells are produced by the special process of division that halves the amount of DNA in the daughter cells, not only is there more scope for mistakes to occur.
			* By the late 1990s, it had been established that human being share 98.4% of their genetic material with the chimpanzee and the gorilla making us, in popular terminology, only « 1% human »
			* The human, chimp, and gorilla lines split from a common stock just 4m ya.
			* Human beings have only about 30k genes, which are capable of making at least 250k proteins. This is only twice as many genes as the fruit fly, and just 4k more than a garden weed called thale cress. A few key genes are different in us, compared with our closest relatives, and these are affecting the way the other genes operate.
	== Outer Space ==		== Outer Space ==

Rob: /* The Realm of Life */

2025-04-05T09:44:40Z

The Realm of Life

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	== The Realm of Life ==		== The Realm of Life ==
			* We are the most complicated things that we know about in the entire universe. This is because, on the cosmic scale of things, we are middle-sized. Small objects, like atoms, are composed of a few simple entities obeying a few simple rules. The universe is so big that the subtleties of even objects as large as stars can be ignored, and the whole cosmos can be treated as a single object made up of a reasonably smooth distribution of mass-energy, again obeying a few very simple laws. But on the scales where atoms are able to join together to make molecules, the number of compounds possible - the number of different ways in which atoms can join together to make molecules - is so great that a huge variety of different things with complicated structures can exist and interact with one another in subtile ways.
			* Life as we know it is a manifestation of this ability for atoms to form a complex variety of large molecules. This complexity starts on the next scale up from atoms, with simple molecules such as water and carbon dioxide; it ends where molecules begin to be crushed out of existence by gravity.
			* Imagine starting out with a set of objects made up of 10 atoms, 100 atoms, 1000 atoms, and so on, with each lump containing ten times more atoms than the one before:
			** The 24th object would be as big as a sugar cube
			** The 27th - about the size of a large mammal
			** The 39th - the size of a rock about a kilometer in diameter
			** The 54th - the size of the planet Jupiter
			** The 57th - about the size of the Sun, where even atoms are destroyed by gravity, leaving a mixture of nuclei and free electrons called a plasma.
			* On this logarithmic scale, people are almost exactly halfway in size between atoms and stars. The realm of life forms like u,s investigated by Charles Darwin and his successors, is between the sizes of sugar lumps and large rocks
			* The role of cells as the fundamental component of living things became clear at the end of the 1850s due to improving microscopic instruments and techniques.
			* Matthias Shleiden (1804-1881), Theodor Schwann (1810-1882), John Goodsir (1814-1867), and Rudolf Virchow (1821-1902) developed the ideas of:
			** All plant tissues are made of cells.
			** All living things are made of cells.
			** Cells arise only from other cells, by division.
			** Every cell is derived from a preexisting cell and disease is no more than the response of a cell (or cells) to abnormal conditions, including tumors, which are derived from pre-existing cells in the the body;
			* The microscopic techniques available at the time were more than adequate to show the structure of the cell as a bag of watery jelly with a central concentration of material, the nucleus.
			* Walther Flemming (1843-1915) - discovered in 1879 that the nucleus contains thread-like structures which readily absorb colored dyes used by microscopists to stain cells and highlight their structure. These became known as chromosomes.
			* August Weismann (1834-1914):
			** Saw chromosomes as the carriers of hereditary information - « heredity is brought about by the transmission from one generation to another of a substance with a definite chemical and, above all, molecular constitution, »chromatin ».
			** Spelled out two kinds of cell division:
			*** For growth and development, all the chromosomes in a cell are duplicated before the cell divides, so each daughter cell obtains a copy of the original set of chromosomes
			*** For production of egg or sperm cells, the amount of chromatin is halved, so that a full set of chromosomes is only restored when two such cells fused to create the potential for the development of a new individual.
			** Showed that the cells responsible for reproduction are not involved with other processes going on in the body, and the cells that make up the rest of the body are not involved with the manufacture of reproductive cells, so that Darwin’s pangenesis and Lamarck’s ideas are both definitely wrong.
			* In 1909, Wilhelm Johannsen, uses term « gene »
			* William Bateson (1861-1926) - coined the term « genetics »
			* Gregor Mendel (1822-1884) - Father of genetics
			** In 1856, began an intensive study of the way heredity works in peas, working with 28, 000 plants, each pollinated by hand
			** There is something in a plant that determines the properties of its overall form. These genes come in pairs, which can be the same, RR or SS, or different, RS. Only one of the genes in a pair, though, is expressed in the individual plant (the phenotype). If the R is ignored and the S expressed, then the S is said to be dominant and the R recessive.
			** With this, Mendel showed that inheritance works not by blending characteristics, but by taking individual characteristics from each parent.
			* Thomas Hunt Morgan (1866-1945)
			** Wanted to disprove (or limit) Mendel’s findings
			** Worked with Drosophila, fruit flies, where there is a new generation every two weeks, with each female laying hundreds of eggs at a time.
			** Drosophila have only four pairs of chromosomes and one pair has a particular significance in all sexually reproducing species.
			** Sex chromosomes are in one of two shapes, X and Y. Females always carry the XX pair, while males always have an XY combination.
			** Different varieties of a particular gene are called alleles.
			** Mendelian heredity and genetics came of age in 195, when he and his colleagues published « The Mechanism of Mendelian Heredity ».
			** « The Theory of the Gene » (1926)
			* The constant reshuffling of the genetic possibilities provided by the process of reproduction encourages diversity, which explains why it is so easy for sexually reproducing species to adapt to changing environmental conditions. Asexual species do evolve, but only much more slowly.
			* In human beings, there are about 30k genes that determine the phenotype. Just over 93% are homozygous - the same on each chromosome of the relevant pair, in all human beings. Just under 7% are heterozygous, which means that there is a chance that there are different alleles for that particular gene on the paired chromosomes of an individual person chosen at random. With some 2000 pairs of genes which come in at least two varieties, no two people on Earth are genetically identical (except for twin who share the same genotype because they come from the same fertilized egg)
			* Friedrich Miescher (1844-1895):
			** Found that the composition of the nucleus was significantly different from that of protein. This substance, the nuclein, contains a lot of carbon, hydrogen, oxygen, and nitrogen, like other organic molecules, but he also found a significant amount of phosphorous, unlike any protein
			** The sperm cell is almost all nucleus, with only a trace of cytoplasm.
			* The building block which gives its name to DNA is ribose, a sugar whose central structure consistas of four carbon atoms linked with an oxygen atom in a pentagonal ring, with other atoms (notably hydrogen-oxygen pairs, OH) attached at the corners. These attachments can be replaced by other molecules, linking the ribose units to them
			** The second building block, which attaches in this way, is a molecular group containing phosphorous, and is known as a phosphate group, acting as a link between ribose pentagons in an alternating chain.
			** The third building block come in five varieties, called bases, known as guanine, adenine, cytosine, thymine, and uracil (G, A, C, T, and U); One base is attached to each of the sugar rings in the chain, sticking out at the side.
			** The ribose pentagons gives the overall molecule its name, ribonucleic acid, or RNA
			** DNA, Deoxyribonucleic acide is almost identical, with one less oxygen atom.
			** RNA contains G, A, C, and U, while DNA contains G, A, C, and T.
			** Covalent bonds - Carbon has six protons in its nucleus (and six neutrons, as it happens), plus six electrons in its cloud. Four bonds is the maximum any atom can make, and bonds are stronger for shells closer to the central nucleus
			** Ionic bonds
			** There is no arbitrariness in the arrangement of electrons in atoms and atoms in molecules - the arrangements which are most stable in the atoms and molecules are always the arrangements with the least energy.
			* X-rays are a form of electromagnetic wave, like light but with shorter wavelengths
			* In a substance like sodium chloride there are no individual molecules (NaCl), but an array of sodium ions and chlorine ions arranged in a geometric pattern

	== Outer Space ==		== Outer Space ==

Robert.adlington: /* Inner Space */

2025-04-04T14:51:52Z

Inner Space

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 == Inner Space ==
 == The Realm of Life ==
 == Outer Space ==

Rob: /* The Last Hurrah of Classical Science */

2025-04-02T19:57:57Z

The Last Hurrah of Classical Science

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	** On 4 July each year, the Earth is furthest from the Sun and is moving at its slowest, and on 3 January it is at its closest, but the difference is only about 3% of the average 150km distance.		** On 4 July each year, the Earth is furthest from the Sun and is moving at its slowest, and on 3 January it is at its closest, but the difference is only about 3% of the average 150km distance.
	** The Earth wobbles like a spinning top over the course of each 22k years, suggesting an alternating cycle of ice ages in the northern and southern hemispheres, but this last point turns out to be wrong		** The Earth wobbles like a spinning top over the course of each 22k years, suggesting an alternating cycle of ice ages in the northern and southern hemispheres, but this last point turns out to be wrong
			* Climate is determined by the distance of a planet from the Sun, the latitude of interest, and the angle at which the Sun’s rays strike the surface at that latitude. The key to Ice Ages is cool summers, not extra-cold winters. The last Ice Ages was intense about 80,000 years ago and ended about 10-15k years ago.
			* The natural state of the Earth throughout most of its long history has been completely ice-free. But occasionally, at intervals separated by hundreds of millions of years, one or other hemisphere is plunged into a period of cold lasting for several million years, an Ice Epoch. There was an Ice Epoch lasting for about 20m years in the Permian and ending about 250m years ago
			* After the Permian Ice Epoch ended, the world was warm for 200m years, while the dinosaurs flourished, but it started cooling again 55m years ago and by 10m years ago, glaciers returned.
			* For the last 5m years, the Earth has been in what may be a unique state, with ice caps over both poles. In this period we have seen a succession of full Ice Ages about 100k years long, separated by warmer Interglacials like the present day, lasting about 10k years. The present Interglacial could be coming to an end naturally in a couple of thousand years — less time than the span of recorded history.
			* It may be this unusual sequence of Ice Ages and Interglacials caused by continental drift that provided suitable selection pressures for us to break away from our hominid cousins and ratchet up our intelligence and adaptability as the key requirements for survival on the fringes of forests.

	== Inner Space ==		== Inner Space ==

Robert.adlington: /* The Last Hurrah of Classical Science */

2025-04-02T05:50:11Z

The Last Hurrah of Classical Science

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	== The Last Hurrah of Classical Science ==		== The Last Hurrah of Classical Science ==
			* Radioactivity is discovered at the end of the 19th C, turning geology into geophysics, providing a way to keep the Earth warm inside for long enough (and stars shining long enough) to support the increasingly long estimates of the age of the Earth (and the Universe).
			* Radioactivity howed that the Earth's interior was not, in fact, cooling dramatically at all
			* Permanentism held that continents were always continents and oceans always oceans, while contractionism was a variant of catastrophism
			* Eduard Suess (1831-1914):
			** Proposed that Australia, India and Africa were fragments of Gondwanaland, an ancient landmass.
			* Alfred Wegener (1880-1930):
			** Father of the theory of continental drift
			** Greenland expedition in 1912-3
			** "The Origin of Continents and Oceans" (1915)
			** Saw that the continents and ocean floors are fundamentally different
			** Proposed that there was once a single supercontinent, Pangea, which had broken up to create today's continents, but had no reason for its breakup.
			** Died on second Greenland expedition in 1930
			* We now know that the Atlantic is widening at a rate of a few centimeters a year
			* Arthur Holmes (1890-1965)
			** More than any other, "the man who measured the age of the Earth".
			** "Principals of Physical Geology" (1944) - a nod to Lyell
			** Apart from the radioactive heating, the key component was time - "solid" rock, warmed from beneath, could stretch and flow, like very thick treacle, but only very slowly. Convection currents inside the Earth, coming from heat generated by radioactive decay broke up Pangea. These currents would move continents at a rate of about 5cm/yr, so the Atlantic could be made from an initial crack over a period of about 100m years.
			* In the early 20th C can now date sample of rock from the proportions of lead and uranium isotopes they contain, and these rocks ere much older than would be allowed by the idea of heat being released from the Sun only as a result of its gravitational collapse.
			* Walter Elsasser (1904-1991):
			** The Earth's magnetism is generated by a natural internal dynamo
			* Edward Bullard (1907-1980):
			** The Earth's magnetic field is the product of circulating conducting fluids in the hot fluid core (basically convection and rotation in molten iron)
			** The "Bullard fit" of the continents, published in 1965, shows them all stuck together in a single landmass.
			* Rocks are magnetised when they are laid down, as molten material flowing from volcanoes or cracks in the Earth's crust, and once set they preserve the pattern of the magnetic field in which they formed, becoming like bar magnets, but realized that not all rocks are magnetized in the same direction and there is evidence that the geomagnetic field had flipped at some time in the past. Maybe this is due to the core's dynamo dying out and then building again in the opposite sense. The Sun also has magnetic reversal every 11 years or so, linked to the sun spot cycle.
			* Much more knowledge of the sea bed, which is two-thirds of the Earth's surface.
			* In the 1960s, see the ocean basins as the sites of action in continental drift with the continents being just carried along for the ride.
			* The Atlantic is getting wider and the Pacific is narrowing. Eventually, America and Asia will collide, while the Red Sea is a new region of upwelling activity, which will splinter Africa away from Arabia to the east.
			* The sea floor spreading is like a slow conveyor belt, endlessly looping round and round, but over the surface of the planet, everything cancels out and the planet stays the same size.
			* Tuzo Wilson (1908-1993) - Coined the term "plate" for the rigid portions of the Earth's crust.
			* Plate tectonics - seismically quiet regions of the globe are quiet because they form rigid plates (six large ones and about twelve small ones, covering the entire surface of the globe):
			** An individual plate may be just oceanic crust, just continental crust, or both.
			** Most of the interesting geological activity on Earth is happening at the boundaries between plates (plate margins).
			** Constructive margins are where new oceanic crust is being made at ocean ridges and spreading out on either side.
			** Destructive margins are where one plate is being pushed under the edge of another, going down at an angle of 45 degrees and melting back into the magma below
			** Conservative margins are where plates are merely rubbing sideways against each other as they rotate (eg San Andreas Fault)
			** Mountain ranges and former sea beds in the hearts of continents today, show that this activity has been going on since long before the breakup of Pangea, and that supercontinents have repeatedly broken up and rebuilt in different patterns.
			* Louis Agassiz (1807-1873):
			** Coined the term "Ice Age"
			** "Studies on Glaciers" (1840)
			** Compared to a Great Flood, glaciation was uniformitarian.
			* Joseph Adhémar (1797-1862):
			** "Revolutions of the Sea"
			** On 4 July each year, the Earth is furthest from the Sun and is moving at its slowest, and on 3 January it is at its closest, but the difference is only about 3% of the average 150km distance.
			** The Earth wobbles like a spinning top over the course of each 22k years, suggesting an alternating cycle of ice ages in the northern and southern hemispheres, but this last point turns out to be wrong

	== Inner Space ==		== Inner Space ==

Rob at 16:52, 1 April 2025

2025-04-01T16:52:30Z

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	** Einstein explained Brownian motion, the jerky, zig-zag fashion of grains in water. The motion might be caused by the impact of molecules with the grains. A better way might be in statistical terms. The process is now known as a « random walk » and the statistics behind it turn out to be important, for example, in describing the decay of radioactive elements.		** Einstein explained Brownian motion, the jerky, zig-zag fashion of grains in water. The motion might be caused by the impact of molecules with the grains. A better way might be in statistical terms. The process is now known as a « random walk » and the statistics behind it turn out to be important, for example, in describing the decay of radioactive elements.
	** The blue color of the sky is caused by the way light is scattered by the molecules of gas in the air itself.		** The blue color of the sky is caused by the way light is scattered by the molecules of gas in the air itself.

			== Let There Be Light ==
			* Francesco Grimaldi (1618-1663)
			** Diffraction - direct evidence that light travels as a wave
			* Euler published his model of light in 1746 and specifically made the analogy between light waves and sound waves and described the Sun as « a bell ringing out light »
			* Thomas Young (1773-1829)
			** Explained the focusing mechanism of the eye (the way muscles change the shape of the lens of the eye)
			** Explained astigmatism as an uneven curvature in the cornea.
			** First person to appreciate that color vision is produced by a combination of three primary colors (red, green, and blue) which affect different receptors in the eye and explained color blindness as a failure of one or more sets of these receptors
			** Played a leading role in deciphering the Rosetta Stone.
			** « Outlines of Experiments and Enquiries Respecting Sound and Light » (1800) - proposing that different colors of light correspond to different wavelengths.
			** The idea of interference in light waves (like interfering ripples on a pond).
			** Calculated the wavelength of red and violet light
			** Young’s double slit experiment - where there can be dark where the peaks and troughs of two light waves cancel each other out.
			* Augustin Fresnel (1788-1827):
			** Developed an efficient lens made of concentric annular rings of glass, each with a slightly different curvature (the Fresnel lens)
			* William Wollaston (1766-1828):
			** Discovered the elements rhodium and palladium
			* Josef von Frauenhofer (1787-1826):
			** Frauenhofer lines
			** Diffraction grating
			** Counted 576 dark lines between the red and violet ends of the spectrum and proved that they were a property of the light itself
			* Robert Bunsen (1811-1899) and Gustav Kirchoff (1824-1887):
			** Each element, when hot, produces a characteristic pattern of bright lines in the spectrum, like the pair of yellow lines associated with sodium. Each pattern is as distinctive as a fingerprint or a barcode.
			* Norman Lockyer (1836-1920):
			** Identified Helium based on the fact that it had an unknown fingerprint.
			* Michael Faraday (1791-1867):
			** Oersted had discovered in 1820 that there is a magnetic effect associated with an electric current and when a magnetic compass needle is held over a wire carrying an electric current it is deflected to point across the wire at right angles.
			** Faraday realized that the wire should be forced to move in a circle around a fixed magnet - « The effort of the wire is always to pass off at a right angle from the pole of the magnet, indeed to go in a circle around it.
			** This is the basis of the electric motor - sixty years later, electric trains were running in Germany and the USA.
			** Liquefies chlorine in 1823.
			** Discovers benzene in 1825, which had the archetypal ring structure of importance to the molecules of life.
			** If an electric current can induce a magnetic force, can a magnet induce an electric current.
			** An electric current passing through a wire wound in a helix/coil would make it act like a bar magnet with poles, and if it is wound round an iron rod, the rod becomes a magnet when the current is turned on.
			** Invented the electric generator or dynamo, which uses the relative motion of coils of wire and magnets to generate electric currents.
			** Introduced terms « electrolyte », « electrode », « anode », « cathode », and « ion ».
			** Introduced concept of « lines of force » in 1831
			** In 1832, suggested that magnetic forces take time to travel across space, proposing that a wave motion was involved and making a tenuous connection with light
			** Magnetic, electric, and gravitational lines of force filled the Universe, according to Faraday, and were the reality with which the seemingly material entities that make up the world are interconnected. The material world, from atoms to the Sun and Earth and beyond, was simply a result of knots in the various fields.
			* James Clerk Maxwell (1831-1879):
			** Definitively explained light as an electromagnetic phenomenon
			** His work on color vision was the foundation for color photography, for color TV and computer monitors.
			** Published a set of four papers On Physical Lines of Force (1861-2) - « light consists in the transverse undulations of the same medium which is the cause of electric and magnetic phenomena. »
			** « A Dynamical Theory of the Electromagnetic Field » (1864) - summed up all of classical electricity and magnetism in four equations (Maxwell’s equations). This unified electricity and magnetism in the electromagnetic field.
			** Placed alongside Newton in the pantheon of great scientists - Newton’s laws and Maxwell’s equations explained everything known to physics at the end of the 1860s.
			** Introduced the constant c, which is the speed of light (299,792,458 m/s) - Light (including radiant heat and other radiations, if any) is an electromagnetic disturbance in the form of waves propagated through the electromagnetic field according to electromagnetic laws;
			** Predicted radio waves.
			** « Treatise on Electricity and Magnetism » (1873)
			** Set up and led the Cavendish Laboratory from 1874.
			* Heinrich Hertz (1857-1894)
			** Confirmed the existence of radio waves, showing that they travel at the speed of light and can be reflected, refracted and diffracted.

			== The Last Hurrah of Classical Science ==

			== Inner Space ==

			== The Realm of Life ==

			== Outer Space ==

Rob: /* Atoms and Molecules */

2025-03-30T12:49:47Z

Atoms and Molecules

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 ** First law - heat is work
 ** Second law - Heat cannot, of its own volition, move from a colder object to a hotter object. Things wear out - everything wears out, including the Universe itself
 * Rudolf Clausius (1822-1888)
-** Defined « entropy ».
+** Defined « entropy ». it always increases. It is only possible for order to be preserved or to increase in local regions, such as the Earth, where there is a flow of energy from outside (ie the Sun) to feed off. But it is a law of nature that the decrease in entropy produced by life on earth feeding off the Sun is smaller than the increase in entropy associated with the processes that keep the Sun shining, whatever they may be. This cannot go on for ever - the supply of energy from the Sun is not inexhaustible.

Rob at 11:36, 30 March 2025

2025-03-30T11:36:59Z

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	** Helped to establish science as a profession that people were paid to do.		** Helped to establish science as a profession that people were paid to do.
	* Darwin was the first scientist listed here who was born after 1800. Wallace was the first who dies after 1900.		* Darwin was the first scientist listed here who was born after 1800. Wallace was the first who dies after 1900.

			== Atoms and Molecules ==
			* During the 19th C, science shifts from being a gentlemanly hobby to a well-populated profession
			* Humphry Davy (1778-1829):
			** Learned French and red Lavoisier’s Traité Elémentaire in the original French
			** Carried out experiments with nitrous oxide (laughing gas) and discovered that it could be used during surgical operations
			** Saw a significant relationship between chemistry and electricity.
			** Royal Instituation established by Count Rumford in 1799 and he became its director in 1802
			** One of the last great amateur scientists and also one of the first professional ones.
			** 1806 - Isolated two previously unknown metals and called them potassium and sodium.
			** 1810 - isolated and named chlorine. Defined an element as a substance that cannot be decomposed by any chemical process, showed that chlorine is an element, and established that the key component of all acids is hydrogen, not oxygen.
			** Appointed Michael Faraday (his eventual successor) as an assistant in the RI
			** Designed the famous miners’ safety lamp which bears his name.
			** In 1820, elected President of the Royal Society
			* John Dalton (1766-1844)
			** When he was born, there were perhaps 300 scientists in the world, when he started work there were a thousand, by his death 10k, and by 1900 100k. The number of scientists doubled every 15 years (though generally populations were doubling over longer periods)
			** Recorded daily meteorological observations daily from 1787 until his death.
			** Discussed the nature of water vapour and its relationship to air, describing it in terms of particles which exist between the particles of air, so that the equal and opposite pressures of the surrounding air particles on a particule of vapour cannot bring it nearer to another particle of vapour, without which no condensation can take place - a precursor to his atomic theory.
			** Was color-blind and did a detailed analysis of the condition, which became known as Daltonism
			** In 1801, came up with the law of partial pressures, which says that the total pressure exerted by a mixture of gases in a container is the sum of the pressures each gas would exert on its own under the same conditions.
			** In the early 1800s became convinced that each element was made up of a different kind of atom, what made one element different from another was the weight of its atoms, and that elementary atoms could be neither created nor destroyed (though they could combine to form « compound atoms » (molecules).
			** The main flaw in the model is that he did not realize that elements such as hydrogen are composed of molecules, not individual atoms and so he got some combinations wrong.
			** A New System of Chemical Philosophy (1808)
			* It took almost half a century for the Daltonian atom to become really fixed as a feature of chemistry
			* Jöns Berzelius (1779-1848):
			** One of the first people to formulate the idea that compounds are composed of electrically positive and negative parts
			** Studied 2000 different compounds over 6 years
			** Invented the modern alphabetical system of nomenclature for the elements.
			** Isolated and identified several elements, including selenium, thorium, lithium and vanadium
			** Chemists were beginning to group elements into families with similar properties. He gave the name « halogens » (meaning salt-formers) to the group including chlorine, bromine, and iodine.
			** Coined the terms « organic chemistry », « catalysis », and « protein »
			** Textbook of Chemistry (1803)
			** Experimenters had long been aware that everything in the material world falls into one of two varieties of chemical substances. Some can be heated and seem superficially to change their character (glowing red hot, melting, evaporating, etc), but when cooled, revert back to the same chemical state they started from. Others, such as sugar or wood, are completely altered by the action of the heat, so that it is very difficult to « unburn » a piece of wood. In 1807, he formalized the distinction. The first, associated with non-living systems, he called « inorganic », and the second, associated with living systems, « organic ». It became clear that organic materials are made up of much more complex compounds, but there was also belief in a vague « life force ».
			* Joseph Louis Gay-Lussac (1778-1850)
			** In 1809 published that gases combine in simple proportions by volume, and that the volume of the products of the reaction (if they are also gaseous) is related in a simple way to the volumes of the reacting gases.
			* Amadeo Avogadro (1776-1856):
			** In 1811, gave the hypothesis that at a given temperature, the same volume of any gas contains the same number of particles.
			** Realized that oxygen and other elements could exist in polyatomic molecular form. Two volumes of hydrogen contain twice as many molecules as one volume of oxygen, and when they combine, each oxygen molecule provides one atom to each pair of hydrogen molecules, making the same number of molecules as there were in the original volume of Hydrogen.
			* William Prout (1785-1850):
			** Suggested that the atomic weights of all elements are exact multiples of the atomic weight of hydrogen, implying that in some way heavier elements might be built up from hydrogen.
			** In the 20th C, with the discovery of isotopes (atoms of the same element with slightly different atomic weights, but each isotype having an atomic weight a precise multiples of the weight of one hydrogen atom) the puzzle was resolved (since chemically-determined atomic weights are an average of those of all the isotopes of an element present, and Prout’s hypothesis was confirmed.
			* Friedrich Wöhler (1800-1882):
			** Accidentally discovered that organic materials could be manufactured from substances that had never been associated with life and the definition of organic changed. There was no mysterious life force.
			** Organic compounds are often complex, containing elements of different elements, and they all contain carbon, which is the reason for their complexity.
			* Now we say that an organic molecule is any molecule containing carbon and organic chemistry is the chemistry of carbon and its compounds. Life is seen as a product of carbon chemistry, obeying the same chemical rules that operate throughout the world of atoms and molecules. Natural selection tells us that we are part of the animal kingdom with no evidence of a uniquely human soul. Chemistry tells us that animals and plants are part of the physical world, with no evidence of a special « life force ».
			* Edward Frankland (1825-1899)
			** Analyzed valency, a measure of the ability of one element to combine with another or as soon became clear, the ability of atoms of a particular element to combine with other atoms.
			* Archibald Couper (1831-1892):
			** Introduced the concept of « bonds », simplifying the representation of valency. Hydrogen is now said to have a valency of 1, meaning that it can form one bond with another atom. Oxygen has a valency of 2, meaning that it can form two bonds. Nitrogen has a valency of 3 and carbon has a valency of 4, so it can form four separate bonds with four separate atoms, including other atoms of carbon at the same time.
			** He saw that organic chemistry might consist of a chain of carbon atoms holding hands with other atoms attached to the spare bonds at the sides of the chain.
			* Friedrich August Kekulé (1829-1896):
			** Saw that carbon atoms could link up in rings (often six atoms in a hexagon) with bonds sticking out from the ring to link up with other atoms or other rings of atoms.
			* Stanislao Cannizzaro (1826-1910)
			** Drew the essential distinction between atoms and molecules
			** Showed how the observed behavior of gases together with Avogadro’s hypothesis could be used to calculate atomic and molecular weights relative to the weight of one hydrogen atom, and drew up a table of atomic and molecular weights.
			* John Newlands (1837-1898):
			** Realized that if the elements are arranged in order of their atomic weight, there is a repeating pattern in which elements at regular intervals, with atomic eights separated by amounts that are multiples of eight times that of hydrogen, have similar properties.
			* Dmitri Mendeleev (1834-1907):
			** Principles of Chemistry (1868, 1870)
			** On the Relation of the Properties to the Atomic Weights of Elements
			** Rearranges the elements slightly in order to make them fit the pattern he had discovered and leaves gaps in the periodic table for elements which had not yet been discovered.
			** It turns out that the chemical properties of an element depend on the number of protons in the nucleus of each atom (the atomic number), while its atomic weight depends on the total number of protons plus neutrons in the nucleus
			** By 1871 he had refined his table to incorporate all of the 63 known elements, with three gaps, which would be filled over the next 15 years with just the properties predicted by him - gallium (1875), scandium (1879) and germanium (1886)
			** From a mass of data, Mendeleyev found a pattern and made a prediction that could be tested by experiment, and found a deep truth about the nature of the chemical world.
			* Themodynamics frew out of the industrial revolution and fed back into it. At the beginning of the 19th C, there was no consensus about the nature of heat, the term was coined in 1849 by William Thomson, by the 1860s the basis laws and principles had been worked out, and 40 years later would be used in a definitive proof of the reality of atoms.
			* Sadi Carnot (1796-1832)
			** Réflexions sur la puissance motive du feu (1824) - analyzed the efficiency of engines converting heat into work, provided a scientific definition of work, showed that work is done as heat passes from a higher temperature to a lower temperature, and even suggested the possibility of the internal combustion engine.
			** First person to appreciate that heat and work are interchangeable and worked out how much work a given amount of heat can do.
			Julius Robert von Mayer (1814-1878):
			** Knew Lavoisier’s work which showed that warm-blooded animals are kept warm by the slow combustion of food, which acts as fuel, with oxygen in the body. He knew that bright red blood, rich in oxygen, is carried around the body from the lungs in arteries, while dark purple blood, deficient in oxygen, is carried back to the lungs by veins.
			** Realized that the reason why the venous blood was rich in oxygen was that in the heat of the tropics the body had to burn less fuel (and therefore consume less oxygen) to keep warm. He saw that this implied that all forms of heat and energy are interchangeable - heat from muscular exertion, the heat of the Sun, heat from burning coal, or whatever - and that heat, or energy, could never be created but only changed from one form to another.
			* James Joule (1818-1889):
			** Gave two lectures in Manchester in 1847 setting out the law of conservation of energy and its importance to the physical world.
			** The Joule-Thomson effect - the way in which gases cool as they expand, the principle on which a refrigerator operates.
			* William Thomson/Lord Kelvin (1824-1907):
			** Responsible for the success of the first working transatlantic telegraph cable
			** Established thermodynamics as a scientific discipline in the middle of the 19th C.
			** Established the absolute scale of temperature, which is based on the idea that heat is equivalent to work, and that a certain change in temperature corresponds to a certain amount of work. There is a minimum possible temperature (-273C) at which no more work can be done because no heat can be extracted from a system.
			* Laws of thermodynamics:
			** First law - heat is work
			** Second law - Heat cannot, of its own volition, move from a colder object to a hotter object. Things wear out - everything wears out, including the Universe itself
			* Rudolf Clausius (1822-1888)
			** Defined « entropy ».