Maybe this is of interest to some of you: Steve McCoy at early television.org kindly lent me a print copy of Peter Yanczer's great but out of print book "The Story of Mechanical Television" and I scanned it. You can find the pdf here: http://gebseng.com/media_archeology/reading_materials/Peter_F_Yanczer-The_Mechanics_of_Television.pdf. Unfortunately, the OCR did not work very well, so I decided to stick with the scanned pages in the pdf.
best,
geb