sentences:  But no written evidence can be found to support this.While still in Rinteln, in Buschmann's letters to his sun Eduard, it appears that Friedrich built a bigger version of an aeoline in 1829, with bellows and piano keyboard of two octaves, which, being about the size of a small writing desk, was still much smaller than any comparable fixed key instrument they had built previously.It is certain that they must have become aware of all kinds of modern developments in this area as they travelled through different countries, which contributed to Friedrich's further refinement of the physharmonica.