After realizing that some quantum mechanics is needed in “History of astronomy from the early 20th century to the early 21st century” and “Discrete area spectrum and the Hawking radiation spectrum I,” I divided “Historical Introduction to Quantum Mechanics” to two parts, and placed the first part in front of the section “Astronomy.” The first article is not about quantum mechanics, but a prerequisite to the next two articles. These three articles do not assume any knowledge of physics.