Monday, February 25, 2013

Heinrich Lenz

Heinrich Friedrich Emil Lenz was born on February 12, 1804 in Dorpat in the Russian Empire, which is now Tartu, Estonia. He studied theology at the University of Dorpat from 1820 to 1823, but switched to physics. After graduation he served as a scientist with navigator Otto von Kotzebue's third circumnavigation of the world, from 1923 to 1926, where he studied climate and took salinity and specific gravity measurements of sea water. He published several papers based on this trip, and in 1832 published his first paper on electromagnetism. From 1840 to 1863 he was dean of physics at the University of St. Petersburg and he served as rector there from 1863 until his death.

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:

National High Magnetic Field Laboratory; "Heinrich Friedrich Emil Lenz (1804-1865)" Retrieved from:

Heinrich Lenz Wikipedia Entry

Monday, February 18, 2013

Tobias Mayer

Tobias Mayer was born on February 17, 1723 in Marbach a small town on the Neckar river a few miles from Stuttgart. His father was a cart-wright and an engineer who made water systems. When Mayer was young he plagued his mother with requests for paper and writing supplies to copy his father's water system plans. Mayer was orphaned when he was 8 and after a time in an orphanage he was taken on by a shoemaker named Gottlieb Kandler, from whom he learned geometry and architecture. Mayer attended the Latin school in Esslingen where he studied mathematics on his own and reached the top class in two years. He published a book on geometry when he was 18. He attempted to become a artillery officer but circumstances prevented him realizing this goal. He became an excellent map maker and in 1746 he joined the Homann Cartographic Bureau in Nuremberg. In 1751 he was appointed professor of mathematics and economy at the Georg August Academy in Gottingen.

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

Tobias Mayer Wikipedia Entry

Sunday, February 10, 2013

Victor Hensen

Christian Andreas Victor Hensen was born on February 10, 1835 in Schleswig, which is now part of Germany. His father Hans Hensen was the director of a school for the deaf in Schleswig and his mother, Henriette, was the daughter of the court physician. Hensen graduated from the cathedral school in Schleswig in 1845 and the grammar school at Glukstat, in Holstein in 1854. He studied medicine at the universities of Wurzburg, Berlin, and Kiel, passing his final examination in 1858. In 1859 he completed his thesis on epilepsy and urinary secretions. After finishing his doctorate he worked as a prosector at the University of Kiel. He was appointed professor of physiology in 1871 and he remained there until 1911. In 1867 he became a member of the Prussian House of Representatives. From 1878 he was the director of the institute of physiology at Kiel. In addition to his work on physiology, Henesen was also an oceanographer and lead many oceanographic expeditions.

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

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

Wilhelm Ludvig Johannsen

Wilhelm Ludvig Johannsen was born on February 3, 1857 in Copenhagen, Denmark. He was the son of a Danish Army officer, Otto Julius Georg Johannsen, and Anna Margarethe Dorthea Ebbson. He mastered many languages when he was still young and he passed his qualifying exams, but was unable to go to a university because his family lacked the means, so he was apprenticed to a pharmacist in 1872, For the next seven years he worked as a pharmacist in Denmark and Germany. In his spare time he studied chemistry and botany. In 1879 he returned to Denmark to work as a chemistry assistant in the Carlsberg laboratories where he did his own botany studies. In 1892 he became a lecturer and in 1902 he became a professor at the Copenhagen Agricultural College. In 1905 he was appointed professor of plant physiology and in 1917 he was made rector at the University of Copenhagen.

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:

Stankus, Tony; "Wilhelm Ludvig Johannsen"; in Biographies of Scientists for Sci-Tech Libraries: Adding Faces to Facts; Psychology Press; 1991

Whilhelm Johannsen Wikipedia Entry