The diameter of the ``Langmuir film'' (b) around warm filaments in gases was at first determined by Langmuir's own method in A, Kr and N2. The calculated film thickness beside a plane surface is 3.3 mm, 1.4 mm and 4.3 mm, respectively. The said diameter was then redefined as the distance of thermal interaction between two similar, warm filaments; temperature measurements revealed that this conventional definition corresponds to the 90°C isothermals. b is a linear function of the temperature; bt = b1000[1+(t-1000) ·0,000255] and b1000 decreases with increasing molecular weight of the gases. b decreases with increasing gas pressure: b/b1= (p1/p)0.42 and it increases somewhat slower with the diameter of the filament (a) than would correspond to the equation of Langmuir: 2B = b · ln b/a. The detailed temperature field around warm filaments was determined under varied conditions. Evidence was gathered, that although 90 percent of the wattage lost can be accounted for by assuming pure conduction, the gas is definitely moving upwards within the film as well as outside of it.