Condenser telephone
Invention
Invention
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A [patent](/wiki/Patent "Patent") registered by [François van Rysselberghe](/wiki/Fran%C3%A7ois_van_Rysselberghe "François van Rysselberghe") (1846\-1893\) in 1882 is thought to be the original invention of the basis of the phonopore (condensor) method. The technique was developed and improved by Charles Langdon\-Davies in 1890, particularly with the invention of a method to call between phones
Patents were lodged for improved versions of instruments for commercial use including one lodged by Ellis F Frost in 1902\.


Who developed and improved the phonopore method in 1890?