ABSTRACT
The theoretical work on the ow of gases at low pressures through orices and tubes has been discussed in many books on the kinetic theory of gases. Review articles by Steckelmacher (1966, 1974, 1986) and Venema (1973) have also covered this eld. In the next section, we give without proof some general results from the kinetic theory of gases that are needed in the design of atomic beams. The theory of the derivations may also be found in textbooks on heat and thermodynamics that cover the kinetic theory of gases and also in books on vacuum physics.
