In 1880, Francis D. Clarke and M.G. Foster were issued the first US patent for this kind of device.
- An electric telephone switchboard
- A reel to reel tape recorder
- An electric hearing aid
- A stereo record player
In 1880, Francis D. Clarke and M.G. Foster were issued the first US patent for this kind of device.
An electric hearing aid. The invention was called a “Device for Aiding the Deaf to Hear.” It worked by passing sounds through the skull to the inner ear. The inventors never produced it commercially.