Song for the Vox Humana by Cornelis Pameijer (1870 - 1940), organist of the Oude Kerk in Amsterdam from 1907 - 1940.
He wrote this piece as an ode to the beautiful Vox Humana of the Vater/Müller organ of the Oude Kerk in Amsterdam.
I think the Vox Humana of the Bätz organ in Utrecht is also beautiful ;)