Köhler’s Flötenschule was published by Zimmerman in about 1880. It is an instructor for old style flutes as Köhler never took up a
cylindrical Boehm instrument. He can be seen on the cover holding an old style instrument with an ivory head.
Below is a Modell Zimmerman flute illustration from Zimmerman’s catalogue of 1899. They also made Viennese style flutes with an ivory head and it is thought that these were favoured by Köhler.