1. Inquiry into the Outbreak of Legionnaires';London:,1985
2. Concern about this arose from the practice, dating from the 1930s, of painting dials with a self luminous mixture containing radium-226, which emits a substantial component of highly penetrating radiation. International recommendations in 1967 discouraged this practice in favour of the alternative use ofeither tritium or promethium-147, both of which emit only f3 particles of energy insufficient to penetrate the case of a wrist watch. The use of radium for this purpose has now effectively ceased and, as a consequence, the mean annual effective dose equivalent per person in the United Kingdom from luminous watches is estimated to be 0-6 microsievert.' This figure may be compared with the annual dose due to natural background sources of about 2000 microsieverts. Any corresponding "hazard" is negligible.-C R HILL, professor of physics as applied to medicine
3. General Assembly. Report of the United Nations scientific committee on the effects of atomic radiation;I United Nations,1982