Letter from Arthur W [William] Rücker, The Athenaeum, Pall Mall, to [Joseph] Larmor He has been thinking over Lippmann and thinks he has found a solution, providing a small diagram. This shows a piece of metal in a magnetic field between two gases, where eddy currents will cause heat to flow to the non-magnetic gas. He expands upon this, noting a more interesting case were both gases were oxygen, where heat might be directed by altering one component, making a cycle. But this does not affect the main question, which he sets out. A separate sheet commences: 'In the report of the Paris Conference Lippmann points out that the small variations of density which go on inside a magnetic gas such as oxygen will cause the lines of force to quiver when it is placed in a magnetic field...' 6 June 1901