down fine particles as well as the large ones postulated in the example given. Even for the larger particles, detection under raining and cloudy conditions would be more difficult than under dry and clear conditions. to i The Subcommittee reemphasizes that the implementation of such advice is a calculated risk, probably justified where instruments for detecting radiation are not available. Visible and tactile indices of fallout would provide valuable warning of danger, but any real control of radiation exposure must depend on instruments. 22