Experiments on the flow of gases through porous Pyrex disks at pressures in the range of a few mm Hg are described. For air, hydrogen, and carbon dioxide the specific flow is found to be given byQ=A(MT)12+B&eegr;Tp¯+CM12{1−exp[&agr;0−&bgr;T12]p¯}The significance of this result is discussed.