Corona-Phon, already version 2.1.2
Window and room antenna.
Idzerda was a radio pioneer, founding one of the first radio stations and the first commercial radio station.
For more info on Idzerda: Wikipedia – PCGG
And in Dutch: Inst. Nederlandse Geschiedenis – Idzerda
Wikipedia – Idzerda

From the book Radio voor amateurs of 1926. Originally an English book by Michael Egan, translated/reworked into Dutch by ir. W. Harmsen.