4 many values of the order of 100 d/m remain without parentheses even though it was felt there was no significant cloud of debris in the vicinity. These items have remained unquestioned because they are actually of low activity (say 20 to 50 d/m on counting - day) and have not been used in the analysis. Lastly, no attempt was made to evaluate the air filter data because the poor correlation between gummed papers and air filters provides little | ; de basis for judgement, therefore, no air filter data is questioned.