Yukawa left many notes he wrote when forming concepts and performing calculations during his research. Many of the notes start with a sentence that is logical and well thought out. He describes the background of his research, his opinion and experiments, then proceeds to detailed formula deformation and calculation. His efforts often bore no fruits, so many notes are incomplete. Some sheets are full of nothing but mathematical equations. He used sheets of notepaper and exam paper printed with “Department of Physics, School of Science, Osaka Imperial University.”