Americans rightly perceive the period just after World War II as a time of prosperity and abundant employment when the country's middle class was solidified, but Mr. Mandel points out that the 1950s economy was built on innovations that came in the decades before and was preceded by the Great Depression and a lot of post-war talk about stagnation. He believes we are now at the beginning of another cycle that will lead to dramatic economic growth. It won't happen tomorrow, he said, and, in fact, it may take another 15 years.