Before revision: ); Principles of Electricity applied to Telephone and Telegraph Work, New York City (November 1938), p.58, 257 It was constructed from a small copper disk, of which one side was formed a layer of cuprous oxide .
After revision: ); Principles of Electricity applied to Telephone and Telegraph Work, New York City (November 1938), p.58, 257 It was constructed from a small copper disk, on one side of which,was formed a layer of cuprous oxide .