"Of Mills and Meaning" is in Wind & Water in the Middle Ages: Fluid Technologies from Antiquity to the Renaissance, edited by Steven A. Walton, is published by ACMRS.
"Technology in Middle Earth" is in the J.R.R. Tolkien Encyclopedia, edited by Michael Drout, is published by what used to be Routledge. (More information on how the volume ended up in quite the shape it did can be found here.