The most recent batch of uploads from the Historical Society of Pennsylvania includes a number of documents on Mary’s political involvements
(related to women’s suffrage, the Equal Rights Amendment, and other topics), as well as a number of texts of and notes from lectures she gave — mainly to the Illuminating Engineers Society of Philadelphia in the early 1920’s. The lecture texts are illuminating (pun intended) because she discusses her involvements in developing rheostats. (Mary did not “invent the rheostat,” but she did develop a specific type of rheostat that could be used for dimming lights in equal increments — important for her expressive color organ work.)
You can search the index of the Visibility Project images for tags like “rheostat” and “lecture” to find full lecture texts with more details.