Two prototype tonometers for teaching speech intonation to the deaf, c. 1955 Two prototype tonometers for teaching speech intonation to the deaf
Ellis's tuning fork tonometer; nine cases containing 105 tuning forks giving pitch from 216 to 586.12 vibrations per second, with six holders for forks; hammers & pad to set forks vibrating. Ellis's tuning fork Tonometer 1880
