Linné on line Mathematics in Linnaeus’ time Mathematics past and present Euclid

## Euclid

It is believed that Euclid lived about 300 B.C. in Alexandria – at that time a center of science, with its fantastic library. Euclid's most famous work, *Elements*, contains virtually all the mathematics Greek scholars had arrived at up to that time. A major share of *Elements* is about geometry.

*Euclidean geometry* is geometry on a plane. Here, the sum of angles in a triangle is 180° and a line can be extended to any length whatsoever without meeting itself.

*Non-Euclidean geometry* is geometry on other surfaces than a plane. For example, a triangle drawn on a sphere has a sum of angles greater than 180°. A line extended far enough will meet itself. On a sphere, a line is thus a circle. Theories for non-Euclidean geometry were developed in the 19^{th} century by Lobachevsky and Bolyai, among others.