Gamma-ray counter equipment, in continuous operation at Ottawa, Canada, indicated that considerable radioactive matter fell on January 29 and again on February 7. The decay period of this material was measured and is consistent with the assumption that the material consisted mainly of products of fission. The fall on January 29 came from an explosion on January 27 and the February 7 material appeared to be three to five days old. The quantity can be estimated only very roughly and is thought to be of the order of one microgram radium equivalent per square meter.