Overview8 copies of Wind At Work (Pathfinder). When the sun warms air up, the air becomes lighter, so it rises. The rising air leaves a gap, and cold air moves in to fill that gap, thus making wind. The Explore On Your Own Pioneer and Pathfinder books enable all students to deepen science content knowledge with identical content at two reading levels: Pioneer (grades 2-4) and Pathfinder (grades 4-6). They also provide the opportunity for students to independently apply multiple reading comprehension strategies.