Jordanus Nemorarius

The main importance of Jordanus to this site is that he was a contemporary (one who lived at the same time as another) of Fibonacci. Jordanus, born in Borgentreich, Germany in 1225, wrote many books on arithmetic, algebra, geometry, and astronomy. He was the first to correctly formulate the law of the inclined plane. He used letters to replace numbers and could state general algebraic theorems. However, his use of algebraic notation was not adopted by later writers.

In Jordanus's work with astronomy, he used letters to signify the magnitudes of stars. He wrote two works on mathematical astronomy titled Planisphaerium and Tractatus de Sphaera. In 1260, on his return voyage from the Holy Land, he died at sea.