I have a video on youtube about a crooke's radiometer, and one of the comments referred to a line from wikipedia about thermal transpiration: I also found a thread about this very subject several years back, but the one link I was interested in (a paper in arxiv) was outdated, and I couldn't find the article. None of the links on Google were very trustworthy. I have a problem with this, because the warmer area would create an area of slightly higher pressure, and that would flow to the area of low pressure - the cool side. The idea that the gas would flow from cold to hot would violate my understanding of physics. Is the idea of thermal transpiration accepted in academia, or is it nothing but an analogous urban legend?