A lucid dream is one in which the dreamer is conscious that he or she is dreaming. The name arose by translation from the French ‘rêve lucide’, a concept which was introduced by Léon d’Hervey de Saint-Denys. When I was a student I was very interested in dreams and I came across the idea of lucid dreams in a book by Celia Green. I would not recommend that book since it contains too much parapsychology for my taste. In 1992 I spent a term as assistant professor at Syracuse University and I enjoyed exploring the university library. There I found a scientific book on lucid dreaming by Stephen LaBerge. There it is described how this phenomenon has been studied under controlled conditions. A technique available in that context is monitoring the movement of the eyes. A correlation was discovered between the actual movements of the eyes of a dreaming person and the visual impressions they see. After a subject had reported dreaming about watching a game of ping-pong it was noticed that during this time the dreamer’s eyes had shown regular side to side motions. This opened up a possibility of the dreamer to signal to the outside world. It could be agreed that under certain circumstances (for instance when a lucid period began) they would give a signal by consciously moving their eyes in a certain regular way. This could then be recognized on the trace of the machine recording the eye movements. At that time I spent a lot of time concentrating on my dream life and managed to have a number of lucid dreams. Now I have had none for a long time, which is probably due to lack of attention.
During my stay in Bures sur Yvette in 1994-95 I was a frequent visitor in the library of the Centre Pompidou. I was happy to find a copy of the book ‘Les rêves et les moyens de les diriger’ (dreams and ways to direct them) by d’Hervey de Saint-Denys. I knew his name from my previous reading on dreams. d’Hervey de Saint-Denys studied his own dreams intensively starting at a young age. In 1855 the ‘Académie des Sciences morales et politiques’ in Paris had a prize competition on the subject of sleep and dreams. He did not take part but his dissatisfaction with the essays submitted led him to write a book criticizing them and explaining his own ideas. Later the book was reprinted and I was able to buy a copy. It is available from www.oniros.fr. d’Hervey de Saint-Denys was a well-known sinologist in his day and I find it remarkable how few traces he left. (I now learned from Wikipedia that his translations of Chinese poems were the source of the texts of the songs in ‘Das Lied von der Erde’ by Mahler. I also discovered that he is mentioned in Proust’s ‘Sodome et Gomorrhe’, in connection with China rather than dreams.) It is no doubt typical that it is very difficult to get information about any individual from a hundred or more years ago apart from a rather small number of exceptions. With the computer age it will presumably happen that, concerning individuals, the time we can see into the past will increase steadily.