JOHN DEE (1527-1608)

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JOHN DEE

‘Mathematician, cartographer & astronomer. Prolific author, natural magician, alchemist.’

‘Alternative knowledge and methods of learning. ‘Conversations with Angels’. Human power over the world (neo-Platonism).’

Dee was a Hermetic philosopher, a major influence on the ROSICRUCIANS, possibly a spy – astrologer and adviser to Queen Elizabeth I; he chose the day of her coronation.

One of the greatest scholars of his day. His library in his home in Mortlake, London, contained more than 3,000 books.

Greatly influenced by Edward Kelley (1555- 97), whom he met in 1582; from 1583-1589 Dee and Kelley sought the patronage of assorted mid-European noblemen and kings, eventually finding it from the Bohemian Count Vilem Rosenberg.
In 1589, Dee left Kelley to his alchemical research and returned to England where Queen Elizabeth I granted him a position as a college warden; however he had lost respect owing to his occult reputation. Dee returned to Mortlake in 1605 in poor health and increasing poverty and ended his days as a common fortune-teller.

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PAUL DIRAC (1902- 84)

1928 – UK

‘Every fundamental particle has an antiparticle – a mirror twin with the same mass but opposite charge’

English Physicist Paul Dirac, who developed a wave equation for the electron. --- Image ©

PAUL DIRAC

‘It appears that the simplest Hamiltonian for a point-charge electron satisfying the requirements of both relativity and the general transformation theory leads to an explanation of all duplexity phenomena without further assumption’

1931 – UK

‘A magnetic monopole is analogous to electric charge’

A magnetic monopole is a hypothetical particle that carries a basic magnetic charge – in effect, a single north or south magnetic pole acting as a free particle.

Until recently no one has observed a monopole.

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WILLIAM HENRY BRAGG (1862-1942) WILLIAM LAWRENCE BRAGG (1890-1971)

1912 – England

X-rays scattered from a crystal will show constructive interference provided their wavelength ( λ ) fits the equation

2d sin θ = n λ 

where d is the spacing between atoms of the crystal, θ the angle through which the rays have scattered and n is any whole number

This is the cornerstone of the science of X-ray crystallography.

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X-RAY DIFFRACTIONX-RAY DIFFRACTION

Symmetrically spaced atoms cause re-radiated X...

Symmetrically spaced atoms cause re-radiated X-rays to reinforce each other in the specific directions where their path-length difference, 2d sin θ, equals an integer multiple of the wavelength λ (Photo credit: Wikipedia)

HENRY GWYN JEFFREYS MOSELEY (1887-1915)

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1914 – Manchester, England

‘Moseley’s law – the principle outlining the link between the X-ray frequency of an element and its atomic number’

ca. 1910s --- Physicist Henry Gwyn Jeffreys MOSELEY --- Library Image by © Bettmann/CORBIS

MOSELEY

Working with ERNEST RUTHERFORD’s team in Manchester trying to better understand radiation, particularly of radium, Moseley became interested in X-rays and learning new techniques to measure their frequencies.
A technique had been devised using crystals to diffract the emitted radiation, which had a wavelength specific to the element being experimented upon.

In 1913, Moseley recorded the frequencies of the X-ray spectra of over thirty metallic elements and deduced that the frequencies of the radiation emitted were related to the squares of certain incremental whole numbers. These integers were indicative of the atomic number of the element, and its position in the periodic table. This number was the same as the positive charge of the nucleus of the atom (and by implication also the number of electrons with corresponding negative charge).

By uniting the charge in the nucleus with an atomic number, a vital link had been found between the physical atomic make up of an element and its chemical properties, as indicated by where it sits in the periodic table.
This meant that the properties of an element could now be considered in terms of atomic number rather than atomic weight, as had previously been the case – certain inconsistencies in the MENDELEEV version of the periodic table could be ironed out. In addition, the atomic numbers and weights of several missing elements could be predicted and other properties deduced from their expected position in the table.

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SIR JAMES CHADWICK (1891-1974)

1932 Manchester, England

‘Discovery of neutrons – elementary particles devoid of any electric charge’

In contrast with the Helium nuclei (alpha rays) which are charged, and therefore repelled by the electrical forces present in the nuclei of heavy atoms, the neutron is capable of penetrating and splitting the nuclei of even the heaviest elements, creating the possibility of the fission of 235uranium

Assistant to ERNEST RUTHERFORD, Chadwick’s earlier work involved the showering of elements with alpha particles. The picture that gradually emerged was one of a nucleus that contained a very heavy particle with a positive electric charge. This particle was christened the proton, the hydrogen building block envisaged by WILLIAM PROUT.
A spin-off of this was the deduction that the nucleus of the hydrogen atom, the positively charged proton with an atomic weight of one, was present in larger quantities in the nucleus of every other atom.

Rutherford and Geiger had shown that a helium atom and an alpha particle were the same thing, apart from the positive electric charge carried by the alpha particle.

A helium atom seemed to consist of a nucleus of a pair of protons circled by two electrons. However, a helium nucleus seemed to weigh as much as four protons. The mass of the known components of an atom did not add-up. Protons seemed to account for around half of the weight and were matched in number by an equal amount of negatively charged electrons to counter their positive charge. But the weight of an electron was one-thousandth that of a proton, so approximately half of the atomic weight of the element was unaccounted for.
Chadwick solved the conundrum in 1932 when he re-interpreted the results of an experiment carried out by IRENE and FREDERIC JULIOT-CURIE (Irene was the daughter of PIERRE and MARIE CURIE).
The couple had found in 1932 that when beryllium was showered with alpha particles, the resultant radiation could force protons out of substances containing hydrogen. Chadwick suggested that neutrally charged sub-atomic units, which he named neutrons, with the same weight as protons, could force this reaction and therefore were what made up the radiation that the Curies called gamma rays. Rutherford had hinted at the existence of such a particle in 1920.

The explanation was widely accepted and the riddle of `atomic weight’ had been solved: a similar number of neutrons to protons in the nucleus of an element would make up the remaining fifty per cent of the previously ‘missing’ mass.

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FREDERICK SODDY (more)

The discovery of the neutron made sense of the observation that many elements come in a variety of forms, each with differing radioactive properties such as decay rate. Each form consisted of atoms with a different mass. Frederick Soddy christened these variants ‘isotopes’ in 1911. The idea that each element might be a mixture of atoms of different atomic weights explained why the atomic weights of a handful of elements were not simple multiples of the atomic weight of hydrogen, the most notorious example being chlorine whose atomic weight was 35.5 times that of hydrogen. Most of the variant forms of each element turned out to be radioactively unstable. An element such as chlorine, with more than one stable isotope, is rare.

The various isotopes of an element were merely atoms with the same number of protons in their nucleus but with a different number of neutrons.

artistic representation of atomic disintegration

Thus every atom was composed of electrons, protons and neutrons. The protons and neutrons clung together in a central clump – the atomic nucleus – while the electrons circled in a distant haze. The neutrons were responsible for increasing the weight of the elements without adding any electrical charge. Two protons and two neutrons made a helium nucleus; eight protons and eight neutrons an oxygen nucleus; 26 protons and 30 neutrons an iron nucleus; 79 protons and 118 neutrons a gold; and 92 protons and 146 neutrons a nucleus of uranium. When a radioactive nucleus expelled an alpha particle, it lost two neutrons and two protons and consequently became a nucleus of an element two places lower in the periodic table. When a radioactive nucleus emitted a beta particle, however, a neutron changed into a proton, transforming the nucleus into that of an element one place higher in the periodic table.

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FRANCIS CRICK (USA 1916-2004) JAMES DEWEY WATSON (UK b.1928)

1953 – UK

‘The self reproducing genetic molecule DNA has the form of a double helix’

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WATSON & CRICK

The structure explains how DNA stores information and replicates itself.
The helical strands of DNA (deoxyribonucleic acid) consist of chains of alternating sugar and phosphate groups. Four types of base – adenine (A), cytosine (C), guanine (G) and thymine (T) – form the rungs of the DNA ladder, which can only be linked by hydrogen bonds in four combinations: A-T, C-G, T-A, G-C.

The DNA code is based on the order of these four bases and is carried from one generation to the next. The sequence of base pairs along the length of the strands is not the same in DNAs of different organisms. It is this difference in the sequence that makes one gene different from another.

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CHARLES DARWIN (1809- 82)

1859 – England

‘All present day species have evolved from simpler forms of life through a process of natural selection’

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Organisms have changed over time and the ones living today are different from the ones that lived in the past. Furthermore, many organisms that once lived are now extinct.

The orthodox view was that of the Creationists. According to the Book of Genesis in the Bible, ‘God created every living creature that moves….’. Against this background, thinkers such as French naturalist Jean-Baptist Lamarck developed a picture of how species evolved from single-celled organisms.

Darwin’s breakthrough was to work out what evolution is and how it happens. His insight was to focus on individuals, not species and to show how individuals evolve by natural selection. The mechanism explained how all species evolved to become well suited to their environment. Later commentators have characterized this idea as ‘survival of the fittest,’ but this was never a phrase that Darwin himself used.

Darwin was influenced by CHARLES LYELL’s newly published book ‘Principles of Geology’, showing how landscapes had evolved gradually through long cycles of erosion and upheaval and by ‘An Essay on the Principle of Population’ written in 1798 by THOMAS MALTHUS.

The publication of Darwin’s book ‘On the Origin of Species by Means of Natural Selection’ in 1859 generated social and political debate that continues to this day. Darwin did not discuss the evolution of humans in this book.
In ‘The Descent of Man’, published in 1871, he presented his explanation of how his theory of evolution applied to the idea that humans evolved from apes. In modern form the theory contains the following ideas:

  • members of a species vary in form and behaviour and some of this variation has an inherited basis

  • every species produces far more offspring than the environment can support

  • some individuals are better adapted for survival in a given environment than others

this means that there are variations within each population gene pool and individuals with most favourable variations stand a better chance of survival – the survival of the fittest.

  • the favourable characteristics show up among more individuals of the next generation

there is thus a ‘natural selection’ for those individuals whose variations make them better adapted for survival and reproduction.

  • the natural selection of strains of organisms favours the evolution of new species, through better adaptation to their environment, as a consequence of genetic change or mutation.

Knowledge of DNA has enriched the theory of evolution. The modern view is still based on the Darwinian foundation; evolution through natural selection is opportunistic and it takes place steadily.

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