Typed letter from Walton Clark to Charles F., Sr., thanking Brush for sending latest gravitation paper Charles F. Brush, Sr., Papers Series 1: Correspon Show moreTyped letter from Walton Clark to Charles F., Sr., thanking Brush for sending latest gravitation paper Charles F. Brush, Sr., Papers Series 1: Correspondence Subseries 2: Acknowledgments (1921-1929) Box 2 Folder 14 Show less