4 typed and handwritten letters between T. Martin and Charles F., Sr., discussing historical writings about electricity Martin was working on, a Natio Show more4 typed and handwritten letters between T. Martin and Charles F., Sr., discussing historical writings about electricity Martin was working on, a National Engineering Museum proposal, Brush's contributions to electricity and Brush's current work on gravity. Charles F. Brush, Sr., Papers Series 1: Correspondence Subseries 3: Business and Professional (1876-1931) Box 5 Folder 2 Show less