The importance of a correlation between the sensitivity for airconducted and that for bone-conducted sounds to the differential diagnosis of an auditory disability was recognized in the sixteenth century. Capivaccio, by means of a simple method of test, separated cases of deafness into two types—those in which the bone sensitivity was acute, with the air sensitivity lowered, and those in which deafness to both air-conducted and bone-conducted sounds was present. As a result of his observations he deduced that bone vibrations passed into the cochlea directly through the investing wall, while air vibrations took the route through the middle ear. There were, of course, no tuning forks at that time.
In 1827 the English physicist Wheatstone observed that when the stem of a vibrating fork was applied to the vertex the sound was heard as if it were located in the head. However, when the auditory canal on one side