Letter, from Augustus De Morgan to Sir John Herschel, dated at 7 Camden St. Autograph letter signed by sender. Has long held the view that a pipe underneath the strings of a piano would increase the resonance. Had not conceived such an instrument as John Frederick William Herschel suggested. Why are 3rds and 6ths more agreeable to the ear than 4ths and 5ths? 8 June 1856