It's that time of year again. Perpetually iron-gray skies, puddles, mud, clashing umbrellas, fogged-up train windows, damp shoes and damper spirits. It's "tsuyu": the rainy season, when nature goes into its annual wet-blanket act.

Basil Hall Chamberlain, that acute but skeptical observer of all things Japanese, once wrote that the rainy season was nothing but a tiresome superstition. "The rain," he said, "is always pronounced exceptional. Never, it is alleged, was so wet a season known before, properly conducted years admitting of no rain but in June and the first week or two of July. . . ."

In support of his contrary view, Chamberlain cited statistics for the last quarter of the 19th century showing that while from April through July nearly every other day was rainy, in the flanking months of March and August rain fell as often as one day in three, and in September and October the average number of wet days rose again to one in two. In other words, he concluded cheerfully, it rains all the time in Japan, no matter what the season.