Dr Libby's article was directed to examining the probable accuracy of the biophysical assumptions involved in the radiocarbon method of dating. His method was to show in a series of tables how the radiocarbon content of samples of tested ancient material deviated from the specific radiocarbon content of biosphere carbon calculated for the dates assigned to these samples on 'historical' evidence. Hitherto, radiocarbon dates have normally been presented as a check on those arrived at by 'historical' methods; here Dr. Libby uses 'historical' dates to control the accuracy of the radiocarbon method. His article, though of deep interest to archaeologists and ancient historians, is thus primarily addressed to his fellow scientists. Before following Dr Libby's lead unreservedly, they will wish to know the relative strength and validity of the alleged 'historical' datings [I].