Handwritten letter from Robert Clark to Charles F., Sr., thanking Brush for sending copy of latest gravitation paper Charles F. Brush, Sr., Papers Serie Show moreHandwritten letter from Robert Clark to Charles F., Sr., thanking Brush for sending copy of latest gravitation paper Charles F. Brush, Sr., Papers Series 1: Correspondence Subseries 2: Acknowledgments (1921-1929) Box 2 Folder 13 Show less