Sir, - Just in case the normally excellent and accurate Weather Eye column is prone to errors once in a blue moon, I want to warn Brendan McWilliams to be particularly careful during March! His column on January 30th was not quite accurate. The full moon on January 31st was not the last "blue moon" of the millennium. March will also feature two full moons, on the 2nd and the 31st, making 1999 an especially rare year in having two "blue moon" months. - Yours, etc., Michael Holmes,Slieve Rua Drive,Kilmacud,Co Dublin.