He was deputy leader and scientific coordinator of the successful American expedition to Mount Everest in 1963 that put five Americans and a Sherpa on the summit, although Siri himself did not make it to the summit. About Everest, Siri wrote, Other mountains share with Everest a history of adventure, glory and tragedy, but only Everest is the highest place on earth. More than two-thirds of the earth's atmosphere lies below its summit, and for an unacclimatized man without oxygen, the top of the mountain is more endurable than outer space by only two or three minutes. The primitive, often brutal struggle to reach its top is an irresistible challenge to our built-in need for adventure.