TARDIS were not, its weight would shatter the Earth's surface. In the tie-in novels, the interior of the TARDIS has been known to contain an entire city, encompass an entire parallel Earth, and even dwarf Gallifrey itself when turned inside out. A distinctive architectural feature of the TARDIS interior is the roundel. In the context of the TARDIS, a roundel is a circular decoration that adorns the walls of the rooms and corridors of the TARDIS, including the console room. Some roundels conceal TARDIS circuitry and devices, as seen in the serials "The Wheel in Space" (1968), "Logopolis", "Castrovalva" (1981), "Arc
Working fluid Working fluid A working fluid is a pressurized gas or liquid that actuates a machine or heat engine. Examples include steam in a steam engine, air in a hot air engine and hydraulic fluid in a hydraulic motor or hydraulic cylinder. More generally, in a thermodynamic system, the working fluid is a liquid or gas that absorbs or transmits energy. The working fluid properties are essential for the full description of thermodynamic systems. Although working fluids have a very large number of physical properties which can be defined, the thermodynamic properties which are often required in engineering design and analysis