ON May 4, in the lecture theatre of the Royal Institution in London, a joint discussion on the upper atmosphere was held by the Chemical Society, the Physical Society, and the Royal Meteorological Society. Instead of attempting to cover the whole subject, it was thought advisable to confine the discussion to topics in which the sciences represented by these societies were equally interested: chemical composition, density, and temperature. The electrical state of the upper atmosphere, the study of which is exclusively the domain of the physicist, was for example touched upon only in so far as it has a bearing on the subjects mentioned. Six speakers had been invited briefly to introduce various aspects, and after their contributions a general discussion was opened. Time permitted only a statement of experimental results; their theoretical explanation would probably be an appropriate subject for another meeting.