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Granular microphone in glass tube, 1878-1890

1878-1890

Experimental carbon block microphone, 1878-1890

1878-1890

Powdered graphite microphone, 1878-1890

1878-1890

Experimental carbon pencil microphone, 1878-1890

1878-1890

Experimental microphones with carbon pencils and cups, 1878-1890

1878-1890

Experimental microphone, 1878-1890

1878-1890

Experimental microphone using steel needles and gas carbon, 1878-1890

1878-1890

Granular microphone in bamboo tube, 1878-1890

1878-1890

Powdered graphite microphone, 1878-1890

1878-1890

Powdered graphite microphone, 1878-1890

1878-1890

Cell used in interruptor circuit, 1875-1890

1875-1890

Hughes microphone detector, 1865-1875

1865-1875

Experimental microphones using steel needles and gas carbon, 1878-1890

1878-1890

Home-made Bell telephone receivers, 1875-1890

1875-1890

Experimental wood-charcoal microphones, 1878-1890

1878-1890

Hughes' printing telegraph, 1860.

1860

Experimental microphone, 1878-1890

1878-1890

Three-nail microphone, 1875-1880

1875-1880
Experimental microphone in sound box, consisting of two small blocks of wood-charcoal pressed upon each other by a spring, probably made by David Hughes, England, 1878-1890

Experimental microphone in sound box, 1878-1890

1878-1890
One of a pair of home made Bell telephone receivers, probably made by David Edward Hughes, England, 1875-1890.

one of a pair of home made Bell telephone receivers, 1875-1890

1875-1890
One of a pair of home made Bell telephone receivers, probably made by David Edward Hughes, England, 1875-1890.

one of a pair of home made Bell telephone receivers, 1875-1890

1875-1890
Four granular microphones, three in glass tubes, one in bamboo tube, probably made by David Edward Hughes, 1878-1890

four granular microphones, 1878-1890

1878-1890
One experimental microphone in sound box, consisting of two small blocks of wood-charcoal pressed upon each other by a spring, probably made by David Edward Hughes, England, 1878-1890

One experimental microphone in sound box, 1878-1890

1878-1890
Experimental microphone consisting of carbon pencil in carbon cups, probably made by David Edward Hughes, England, 1878-1890

Experimental carbon pencil microphone, 1878-1890

1878-1890
Granular microphone in glass tube, probably made by David Edward Hughes, England, 1878-1890

granular microphone in glass tube, 1878-1890

1878-1890
Granular microphone in glass tube, probably made by David Edward Hughes, England, 1878-1890

granular microphone in glass tube, 1878-1890

1878-1890
One experimental microphone consisting of steel needles suspended in contact with blocks of gas carbon, probably made by David Edward Hughes, England, 1878-1890

experimental steel needle and gas carbon microphone, 1878-1890

1878-1890