Where is Harry Potter when we need him? For the second year in a row, the nonappearance of Book 5 of the small bespectacled one's magical doings is throwing readers of all ages into a spring tizzy.

May means different things to different people, but it has always seemed to us that, as the pivotal month between winter's cold and summer's heat and rain, it marks a general lightening of mood. Golden Week -- despite the fact that the idea usually outshines the real thing -- is just the beginning of it. All through May, as the temperature rises, the azaleas and wisteria pop and the leaves thicken, we quicken the shift into summer mode. There's no resisting it. Everywhere, people step out in lighter, brighter clothes, dream of vacations, drink white wine instead of red -- and, if they are part of the small coterie of book lovers, start planning their summer reading lists.

Summer books are different from winter's, or they should be: lighter, airier, less taxing; poetry, not philosophy; mysteries, thrillers, romances and travel books rather than politics, economics, history and science. Of course, there are exceptions. This summer, for instance, Mr. Robert Caro's "Master of the Senate," the door-stopper-size, long-awaited third volume of his biography of the late former U.S. president, Lyndon Johnson, promises to provide as much sizzle and intrigue as any tawdry beach thriller. But on the whole, the books we line up for August don't have the intellectual heft of the ones we put aside for New Year's. Which is why "Harry Potter" has proved such a godsend in the past: Each of the first four volumes is the pure, golden essence of a summer book. And it is why frustration is mounting over the repeated postponement of the release of the fifth.