Win′dow-tube.
(Telegraphy.) An insulating device for introducing line wires into telegraphoffices. It consists of a glass or hard rubber tube of any required length, and having a head at one end which is placed inside the building. The iron wire is fastened to an insulator outside and projects through the tube into the office, for 1/4 to 1/2 an inch. A screwthread is cut on its end, which receives a main line binding-post, and from this the copper office wire is run to any part of the room.

