Letter from James Dewar, Royal Institution of Great Britain, London, to [Joseph] Larmor Dewar agrees with Larmor, but can't get out of his problem. He lists values for oxygen, hydrogen, helium and mercury, noting the pressure towards the inner side of the vein [vane?], although he fears there are complications from internal reflections. He hoped the radiometer experiments would settle some points, but it is not so easy. At low temperatures the slightest friction from gas bubbles or touching the side of the vacuum vessel induces an electrical charge. He concludes that he must have special radiometers made if he is to continue the work. 18 July 1907