The color plate titled “Homologous Series of Compounds” by Edward Livingston Youmans illustrates various acids in a homologous series. This plate is part of the “Chemical Atlas; or, The Chemistry of Familiar Objects” authored by Youmans, an American scientific writer, editor, and lecturer. Youmans significantly contributed to popularizing science and founded Popular Science magazine. The image visually conveys the concept of homology, where compounds share similar structural features while differing by a repeating unit (e.g., a CH₂ group). Youmans was also a pioneer in explaining the conservation of energy and the mutual relation of forces in his lectures on the “Chemistry of the Sunbeam” and the “Dynamics of Life.” The plate serves as a valuable educational resource, emphasizing the interconnectedness of chemical compounds and their systematic variations.