https://archive.org/details/alexander-hartung-was-verborgen-bleiben-sollte
https://archive.org/details/prof.-dr.-taschner-die-grossten-zahlen-der-natur
https://archive.org/details/jess-kidd-die-ewigkeit-in-einem-glas-1
https://archive.org/details/jess-kidd-die-ewigkeit-in-einem-glas-2
https://archive.org/details/die-maya-untergang-einer-hochkultur-arte
https://archive.org/details/die-neue-industrielle-revolution-arte