MARATHONS OF THE WORLD Marathon runners, prospective runners, and followers of marathon races will value this photo-illustrated guide to 50 of the world's best marathons. Each marathon is given its own detailed description, which includes--    A rating for comparative difficulty  An expert analysis of the course  The time year when it takes place  Specifics on when and how to enter  Course-specific training tips   Just a small sampling of the marathons described include--   In the U.S. and Canada: Boston, New York, Washington, Toronto, Niagara Falls  In Australia and New Zealand: Auckland, Sydney, the Australian Outback  In Asia: Tokyo, Beijing, the Great Wall of China  In Europe: Rome, Hamburg, Frankfurt, London, Amsterdam, Madrid, Athens, Venice  . . .as well as races in the Caribbean islands, Africa, South America, and even the Antarctic. Approximately 160 vivid photos show many of the events in their colorful settings.