more information from Oto Audiology
Hearing Aids - Audiology
Over 100 years have been made incredible progress in the field of hearing aids; at the beginning the only means to help the patient with auditory deficiency was essentially consists of a large and uncomfortable funnel-shaped device that conveyed the ear sounds.

The advent of electricity and electronics has made an essential contribution to the resolution of the problem by allowing the construction of ever smaller and more powerful devices.

The first units were very simple: a carbon microphone, a battery and a headset; subsequently the valves and transistors have greatly improved amplification and correction of sounds finally microcircuits and digital technology have made today the prosthesis very reliable and almost invisible. 
Dentaphone Cincinnati - 1880
Rare and fragile instrument of the Company Dentaphone Cincinnati - 1880; It was composed of a triple of hard rubber sheet: the sound waves that were invested conveyed to the patient's teeth that could "hear" through the bone transmission. Furthermore, the degree of bending sheets probably allow you to select the frequencies of incoming sounds. Much like the Dentaphone was another device called Audiphone.

In this short pamphlet in 1880 that the public fully below, Prof. Giovanni Paladino (1842-1917), a Neapolitan physiologist, claims to have made a few years before dell'Audiphone and Dentaphone a tool called Fonifero, and calls for It is recognized as a priority in the study and application of transmission of sound through bone conduction; n and in 1876 he had in fact presented this equipment in a scientific journal.

The fork was resting on the neck of the person who spoke, the button on the opposite side was applied to the teeth or bone mastoid.

I leave the reading of its pages the detailed description of the Fonifero.

Reconstruction of Fonifero Prof. Giovanni Paladino
Conversation tube - Cornet acoustique.  
The short-stemmed hearing aids were certainly practical to use, however, obliged to a very close contact with the other party, the horn tube instead allowed to keep a certain distance and in theory helping to prevent the transmission of diseases: Pasteur in those years he had highlighted the danger of infection due to microbes transmitted by air.
the balance of this page is devoted to electrical devices

Ear Trumpets, the Packington Collection
SY10, Shropshire, UK