Louis Turenne was one of the first to plot out the fundamental ray angles in 1935. He put it on a circular format, used a weak solution of radium bromide in the center and would place a sample on there. Then he used a pendulum to find the rays much like an interferometer works. I've never been able to find any of his work other than what I read by Christopher Hills book "Supersensonics". "Two American physicists, Davisson and Germer, found that electrons striking a crystal were reflected from it only in certain directions...It was found that the number of electrons increases considerably at certain angles..."
I found another page for you.
http://wikirota.org/en/Main_Page