TUBE. This term generally refers to a hollow cylinder or pipe for conveying liquids or gases. In botany it denotes the narrow basal portion of a gamopetalous corolla or a gamosepalous calyx.
For a discussion of the manufacture of metal tubing, see the articles on IRON AND STEEL ; CHEMICAL APPARATUS.
The manufacture and application of glass tubing is discussed under GLASS MANUFACTURE. Tubes for boilers (i.e., fire tubing and water tubing), are treated under BOILERS and STEAM GENERA TION. The term as used in the textile industry (i.e., tube yarns), is found in articles related to textiles.
The application of the term to sub-surface transit is found in the article RAILWAYS, TUBE. The article PNEUMATIC CONVEYING treats the use of tubes in postal and similar services. Under TYRE various types of inner tubes for vehicles are described. The Coolidge Tube and tubes used for X-ray treatment and Radio therapy are discussed under articles related to these subjects. The tubes used in lighting are discussed under LIGHTING AND ARTI FICIAL ILLUMINATION. For Estuary Tubes see AQUEDUCTS.
Perhaps the most common use of the word in recent years has been in connection with vacuum tubes used in the radio. These are discussed under THERMIONICS and THERMIONIC VALVE.
Many special tubes applying to different fields of science and industry are found under various headings in their related fields. One device, however, which deserves mention here is the Knowles Grid-Glow Tube or relay. This is a device for control ling electrical power which is so sensitive that it can be operated by the mere approach of the human hand. Superficially the
Knowles Grid-Glow Tube resembles the radio tube for it has the anode, the cathode, and Grid. However, it has no filament ; the connection of the anode and cathode are the reverse of the radio tube ; the grid is merely a piece of heavy wire and the tube is filled with neon, argon, or some other gas. The ordinary relay is a device which is operated by a small current which controls a much larger one. The relays commonly used in electrical en gineering have an amplifying power of about 10,000, which means that they can control a current 10,000 times greater than the current controlling them. A Knowles Grid-Glow Tube has an amplifying power of the order of Ioo,000,000 and it is probably the most sensitive thing of the kind ever devised. The energy required to operate it is about one one-thousand-millionth ( ,o00000000 ) of a watt. This small amount of energy is sufficient to start a current of 25 milli-amperes flowing through the tube. This current is sufficient to close or open a switch of 25 amperes and this in turn to control almost any operation. It is possible by use of this relay to turn on the lights of the city, start a railway train, or manoeuvre a battleship. The tube is the invention of Knowles of the Westinghouse Electric and Manufacturing Co.