In 1859 he began, in concert with Sir William Thomson (afterwards Lord Kelvin), to work on problems respecting the making and use of cables, and the importance of his researches on the resistance of gutta-percha was at once recognized.
Connexion is made into the office (or to the underground system, as is often the case) from the aerial wire by means of a copper conductor, insulated with gutta-percha, which passes through a " leading in " cup, whereby leakage is prevented between the wire and the pole.
Gutta-percha-covered copper wires were formerly largely used for the purpose of underground lines, the copper conductor weighing 40 lb per statute mile, and the gutta-percha covering 50 lb (90 lb total).
copper wires insulated with carefully dried paper of a special quality, has practically entirely superseded the use of wires insulated with gutta-percha.
Owing to the high price of gutta-percha the tendency, of recent years, has been to approximate more closely to the theoretical dimensions, x xvl.