Typed letter from George Appel to Charles F., Sr., thanking Brush for his latest gravitation paper, commenting on the experiments, and expressing disa Show moreTyped letter from George Appel to Charles F., Sr., thanking Brush for his latest gravitation paper, commenting on the experiments, and expressing disappointment tht Brush does not theorize at all Charles F. Brush, Sr., Papers Series 1: Correspondence Subseries 2: Acknowledgments (1921-1929) Box 2 Folder 14 Show less