1.		Telephony : a detailed exposition of the telephone system of the British Post Office / T. E. Herbert; W. S. Procter Autor: Herbert, T. E. Data Publicação: 1946
2.		Telephony : a detailed exposition of the telephone system of the British Post Office / T. E. Herbert; W. S. Procter Autor: Herbert, T. E. Data Publicação: 1946