NATIONAL TELEPHONE COMPANY
Mining and Engine House Telephones
Pattern No.s B390, B395, B400 & B405
A special feature of this pattern instrument is that the arm, to which the receiver is attached, also controls the switching apparatus. When it is required to speak, the switch arm is moved to a horizontal position, thus bringing the speaking circuit into contact, and when released, the ringing circuit is brought into contact.
Last revised: July 07, 2020