With pleasant weather comes a busy hiking season in the White Mountains of New Hampshire. A misread map, a sudden storm, a forgotten headlamp - and suddenly a hike could turn into a matter of survival. We look at a new book, " Critical Hours, " that offers a history and a celebration of the search and rescue workers and volunteers who save lives in the White Mountains. The growth of inexpensive but sophisticated navigation devices and mobile phones have become part of the experience for both