Japan's Emperor Hirohito, the world's oldest and longest reigning monarch, is back at the Imperial Palace after two bouts with a nasty cold and fever during his seven-week vacation at a mountainside villa. Doctors said Hirohito, 87, was now in good health after his temperature had twice clmbed above 100 degrees in the past two weeks. When he was well, the emperor spent his time walking in the garden with his wife and meeting with botanists helping him with his forthcoming book, "Plants at the Imperial Palace."