If you ever walked around Leiden you can’t have missed them: the painted wall formulas of famous scientists from Leiden and the wall poems in a myriad of languages. The poems were an initiative of the two friends Ben Walenkamp and Jan Willem Bruins. Bruins died on the 8th of April, at 74 years old.

Bruins and Walenkamp started painting wall poems in 1992 for the Leiden municipality. Walenkamp designed the entire piece, and Bruins came up with the typography and did the actual painting. Two physicists approached the duo in 2015, asking them if they could also paint physics formulas on the walls of Leiden, formulas from (of course) scientists from Leiden. As a result you can find eight formulas throughout Leiden, next to the 113 (!) poems they made from 1992 onwards. They always have the formula itself, as well as a depiction of what the formula is about, like the gigantic pendulum on the Brandmeester building next to the swing formula by Christiaan Huygens. You probably saw some of them from the train (the law of gases by van der Waals), on the Old Observatory (the Oort-constants), or along the Hogewoerd (the law of refraction by Snellius).

The paintings of Walenkamp, who was the communicator of the team, and Bruins, who behind him was hard at work painting on a scaffold, have become iconic for Leiden. With the spring weather becoming milder, try walking past the Einstein field equations or the electron spin (pictured), and keep Jan Willem Bruins in your thoughts.

Also take a look at:

https://www.youtube.com/watch?v=urnEegneNFo Movie about the wall formulas by the Leiden Institute of Physics (subbed in English).