In 1895 John Perry challenged Kelvin's figure on the basis of his assumptions on conductivity, and Oliver Heaviside entered the dialogue, considering it "a vehicle to display the ability of his operator method to solve problems of astonishing complexity."
En 1895 John Perry puxo en dúbida as cifras de Kelvin baseándose nas súas asuncións sobre a condutividade, e Oliver Heaviside entrou na discusión, considerándoo "un vehículo para mostrar a capacidade do seu método operador para resolver problemas de extraordinaria complexidade."