With reference to all such further refinements of theory, it is to be borne in mind that the perfect fluid of hydrodynamic analysis is not a merely passive inert plenum; it is also a continuum with the property that no finite internal slip or discontinuity of motion can ever arise in it through any kind of disturbance; and this property must be postulated, as it cannot be explained.
We must be content to treat the aether as a plenum, which places it in a class by itself; and we can thus recognize that it may behave very differently from matter, though in some manner consistent with itself - a remark which is fundamental in the modern theory.
The representatives of the states favorable to this proposal, ic, Austria, Luxemburg, Denmark and the four kingdoms, came together in Frankfort on the 4th of September 1850, constituted themselves a Plenum of the old diet and refused to admit the other states except under the terms of the act of 1815.
Colour itself is not objective; it is found not in the ultimate plenum and vacuum, but only in derived objects according to their physical qualities and relations.
See air change, air washer, modulated control plenum system, unit air conditioner, and BS 5643.