### Astronomy Bio...Johann Mayer

#### Jay Bitterman

Johann Tobias Mayer was born in Marbach, Germany on February 17, 1723, the youngest of six children. His father was a cart wright. His family moved to Esslingen shortly after his birth. Both his parents died when he was six and he went to live in an orphanage. In 1739, with his skill in architectural drawing and surveying under the direction of a local artillery officer, he rendered plans and drawings of military installations. He also drew a map of Esslingen and its surroundings which is the oldest in existence. He taught himself mathematics, although it was not offered at his Latin school. In 1741, at the age of 18, he published his first book on the analytical methods to the solution of geometrical problems. During the next few years he learned French, Italian and English. In 1746 he started to work in Nuremberg for the Homann Cartographic Bureau, spending much of his time collating geographical and astronomical facts found in the Homann's archives. In 1750 he published a compilation called *Kosmographische Nachrichten and Sammlungen auf das Jahr 1748. *Because of his prominence as both as cartographer and astronomer, he took the post of Professor at the Georg August Academy in Göttingen.

Mayer's most important work at the Homann Cartographic Bureau, was the construction of some 30 maps of Germany. His precise geographical data, along with accurate astronomical details, was used to determine and establish latitudes and longitudes on Earth. He designed his own telescope in order to observed lunar oscillations and eclipses and to acquire the astronomical details. While at Göttingen he decided to make a map of the Moon's surface, which involved unexplored theoretical and practical work. After many lunar observations he decided that the Moon did not have an atmosphere. After continuous observations with his repeating (or reflecting) circle he published "Mayer's Lunar Tables" in 1753. Because his calculations were accurate to one minute of arc he gained international fame. Starting in 1755 he used a superior instrument made by John Bird that had a 6-foot radius mural quadrant which improved on his earlier stellar observations and enabled him to introduce correction formulae for meridian transits of stars. He also invented a simple and accurate method for calculating solar eclipses, compiled a catalogue of zodiacal stars and studied stellar proper motion. While in the process of devising a method for finding geographical coordinates without using astronomical observations he came up with at a new theory of the magnet. It furnished a convincing explanation of the validity of the inverse square law of magnetic attraction and repulsion.

He died on February 20, 1762, after contracting gangrene. Shortly after Mayer died, his widow acting upon one of his last requests, submitted to the British Admiralty a method for computing longitude at sea. Mayer's widow was awarded £3,000 by the British Government for her husband's claim to a prize offered for such a venture. Later, Mayer's tables were replaced by more accurate data compiled by James Bradley at Greenwich.

Published in the February 2002 issue of the NightTimes