Mean Free Path of Gases by a Direct Method

Apparatus consists of a brass tube partitioned into chambers. Partitions contain small holes which are exactly aligned. Gas is introduced at a pressure of several millimeters at one end; a vacuum is maintained in other chambers by rapid pumping and the molecular beam passing through the aligned holes is measured by impact upon a vane suspended from a quartz fiber. Introduction of a gas in one of intermediate chambers deflects away a definite proportion of the beam giving a direct measure of the mean free path