Monday, February 25, 2013
Lenz is most remembered for his studies of electromagnetism. At the beginning of the nineteenth century scientists were beginning to understand electricity and magnetism, but did not understand the relationships between the two. Lenz took one of the first steps in filling in that gap by formulating Lenz's Law. Repeating the work of James Faraday, Lenz observed that when a electrical current is generated by a changing magnetic field, the magnetic field generated by that electrical current opposes the magnetic field that generated the current (see here for a graphic demonstration of this). This result is due to the law of conservation of energy. Lenz's results were copiously documented so that they could be easily repeated and his quantitative results were more thorough than the qualitative work that had been done previous to him.
In addition to Lenz's Law, Lenz also independently discovered Joule's Law and worked on developing electroplating. Lenz is honored by the use of the letter L to represent capacitance in physics equations.
Lenz died on February 10, 1865, in Rome, after suffering a stroke.
Tooker, J.B.; "A Discussion of the Life of Heinrich Friedrich Emil Lenz"; Retrieved from: jtooker.com
National High Magnetic Field Laboratory; "Heinrich Friedrich Emil Lenz (1804-1865)" Retrieved from: magnet.fsu.edu
Heinrich Lenz Wikipedia Entry
Monday, February 18, 2013
Mayer is mostly remembered for his astronomical observations of the moon. In 1748 and 1749 he made a map of the lunar surface and came to the conclusion that there was no atmosphere on the moon. At the time this was a controversial opinion. His lunar tables, published in 1752, were recommended by the British Astronomer Royal, for their utility in determining longitude while at sea. Mayer's widow received a 3000 pound grant from the British government after bringing them to England.
A crater on the moon is named is named after him. He is often confused with his son, Johann Tobias Mayer, who was a physicist.
Mayer died during the French occupation of Gottingen on February 20, 1762.
Forbes, Eric Gray; "The Life and Work of Tobias Mayer (1723-62)"; Quarterly of the Royal Astronomical Society (1969)8:227-251
Wepster, Steven; "Father and Son Mayer"; Retrieved from staff.science.uu.nl
Tobias Mayer Wikipedia Entry
Sunday, February 10, 2013
Hensen's work was involved with many fields of science including physiology, oceanography, and chemistry. His physiological work included describing the structures of the inner ear. These studies led to the discovery of the Hensen duct, Hensen cells and Hensen stripe. These structures and cells are part of the cochlea, the snail shell shaped structure in the inner ear that is responsible for sensing sound waves. Hensen was also able to extract glycogen from the liver and there was a priority dispute about this between him and Claude Bernard. Now it is known that Hensen verified Bernard's work.
Hensen is most remembered for his coining of the word plankton to describe the microscopic sea organisms that form the basis of the ocean's food chain. These organisms include drifting animals, plants, archea, algae, and bacteria. The term plankton describes an ecological niche rather than a specific type of organism. Because they depend on sunlight they are found in greater numbers on the surface of bodies of water. They are found in oceans and lakes and are an important food source for fish and whales. Hensen developed methods of collecting and studying plankton that are still used today.
Hensen died on April 5, 1924.
Press and Communication Services, University of Kiel; "Famous Scholars from Kiel: Victor Hensen"; Retrieved from www.uni-kiel.de
Raica, M.; "A Short Story of Victor Hensen and a Cell of the Inner Ear"; Romanian Journal of Morphology and Embryology (2012)53:855-857
Victor Hensen Wikipedia Entry
Sunday, February 3, 2013
Johannsen's is best known for his genetic research. He found that there was evidence that natural selection worked in a mixed group of self-fertilizing plants but not individual self-fertilizing plants. This means that in a group of plants that produce genetically identical offspring natural selection selects for some of the plants but individual plants that produce genetically identical offspring are not effected by natural selection and the only differences in offspring are due to environmental factors. This evidence seemed contradict Charles Darwin's theory of evolution, because according to Darwin natural selection gradually changes organisms to better fit their environment. With our modern knowledge of the function of DNA in cells this result makes sense, because we know genetic variation is the result of mutation.
In addition to his research Johannesen was a prolific writer. His genetic textbooks were the most influential of their time. He coined the words "gene", "genotype" and "phenotype". Johannsen was awarded several honorary doctorates, but was appointed professor without having an academically earned doctorate. He was elected to the Danish Royal Academy of Science.
He died on November 11, 1927 in Copenhagen.
Hjermitslev, Hans Henrik; "Wilhelm Ludvig Johannsen (1857-1927)"; retrieved from: darwinakive.dk
Stankus, Tony; "Wilhelm Ludvig Johannsen"; in Biographies of Scientists for Sci-Tech Libraries: Adding Faces to Facts; Psychology Press; 1991
Whilhelm Johannsen Wikipedia Entry