<span>Most of the letters here were written between Charles F. Brush, Sr., and his family members, most notably his son, Charles F. Brush, Jr., and his son’s wife, Dorothy Brush (Walmsley). Unfortunately, not much correspondence exists before 1910. In the letters (dated between 1911 and 1929) between Brush, Sr., his son, and daughter-in-law, they discuss their lives in Cleveland and elsewhere, their travels, scientific experiments, school, and grandchildren. The correspondence also documents how Dorothy and Brush, Sr., coped with the death of Charles F. Brush, Jr., in 1927. The correspondence files also highlight Brush’s efforts to prove his theory of gravitation. </span><span>This theory suggested that the behavior of gravity could be explained by the action of ether. Ether was thought to be a gas which many believed occupied space in which light traveled. Thus, Brush attempted to prove the existence of ether. After many years of conducting his own experiments in his Euclid Avenue home’s basement laboratory to prove the existence of ether, Brush contracted scientists at the U.S. Bureau of Standards and General Electric to further his work. As the correspondence showed, the experiments done at the U.S. Bureau of Standards and General Electric could not prove, to their satisfaction, the existence of ether.Charles F. Brush, Sr., Papers</span>