Abstract
The coefficient for tangential momentum transfer σ between the boundary and a flow of rarefied gas has been investigated by the rotating cylinder technique. Systematic perturbation of the pressure history of the active surfaces were made and correlated with observed variation of σ. A high‐pressure history is found to result in a lowering of σ with time (order of days) from values in the range 0.9 to 1.0 values approaching 0.6. A low‐pressure history is found to result in constant values of σ in the range 0.9 to 1.0. The observations were of the same character for all gases.