Generally believed lost, 12 of Wallace Clement Sabine’s notebooks have been offered by the Riverbank Laboratories, IITRI, of Geneva, Illinois, to Harvard’s rare books library for safekeeping. The Author has indexed the notebooks against Sabine’s published papers and has sought an answer to Sabine’s Silence in the 1900–1904 period following the opening of Boston Symphony Hall. The investigation reveals that all significant data recorded in the notebooks were either submitted for publication priuor to 1915 or were taken in 1915 just before Sabine became involved in World War I scientific service abroad. He died in January 1919. The excising of over 200 pages from his notebooks just after 1900 indicates that he may have been disappointed in his predictions of the reverberation times of Symphony Hall. This paper summarizes the contents of the notebooks and explains the reason for the discrepancy between his predictions and more recent measured reverberation times for Symphony Hall. It protrays the depth of Sabine’s experimentation, his influence on the growth of applied physics at Harvard, his extensive consultation with architects, and his service in the war effort.