7 Typed and handwritten letters between Charles F., Sr., and Richard Fay, in 1920 Brush asking Fay to attempt to put mathematical equations to his gra Show more7 Typed and handwritten letters between Charles F., Sr., and Richard Fay, in 1920 Brush asking Fay to attempt to put mathematical equations to his gravitation theory and Fay's equations, in 1925 and 1926 Fay writes with refined equations and new thoughts. Charles F. Brush, Sr., Papers Series 1: Correspondence Subseries 3: Business and Professional (1876-1931) Box 4 Folder 7 Show less