The Head Voice and Other Problems, by D. A. Clippinger, 1917. Clippinger wrote several books on voice training — this is probably one of his earliest. He also wrote an article for Musical Quarterly (”Scientific Voice Training.” Musical Quarterly, Vol. 4, No. 4 (Oct., 1918), pp. 618-629) but unfortunately I can’t read it, not being a vetted academic.
I post-processed this book for David Newman. It was a nice break from doing my own projects.