Memorial plaque of <a href="https://en.wikipedia.org/wiki/en:Waldemar_Titzenthaler" class="extiw" title="w:en:Waldemar Titzenthaler">Titzenthaler</a>
<a href="//commons.wikimedia.org/wiki/User:R._J._Mathar" title="User:R. J. Mathar">R. J. Mathar</a>
CC BY-SA 4.0
<span class="int-own-work" lang="en">Own work</span>