www.stirlingmaier.com a website relating to hot-air-engines bei der Firma Hubertus Raab, Zeitz, um 1905  (in “comp-07”) Mounting of an Art-Nouveau ventilating fan with hot-air engine manufactured by the Hubertus Raab company, Zeitz in Saxony Montage eines Jugendstil-Ventilators mit Heissluftmotor