Joint Colloquium: Baxter -- The "star-triangle" or "Yang-Baxter" relations in statistical mechanics

There are a number of lattice models, mostly two-dimensional, 
in statistical mechanics that have been solved exactly by using the 
star-triangle relation. By this I mean that the partition function per site 
and the spontaneous magnetization have been calculated in the limit of 
a large lattice. I shall give a historical overview and discuss the
remarkable invariance properties that follow from the star-triangle
relation, indicating how they lead to the solutions.
The talk is intended for a non-specialist audience.