WHAT IS THE FORCE . That drove them on foot across the land bridge from Asia to the New World long before recorded history? That keeps Joshua Warden on the wagon train headed to the California gold fields after losing so much? That is found in a shovel full of prairie soil-demanding that Amos Krebbs put down roots? That directs Stephano Romano's return to the sea? That moved Harry Krebbs from the Kansas prairie and focuses his eyes and those of his astronaut son, Alan, on the far horizon . and beyond? That keeps the feet of industrialist Gilbert Krebbs and Congressman Bobby Dobbson firmly planted in the center? That drives a Monarch butterfly across a thousand miles of desert and mountains to a tiny spot on the California coast, where she has never been, but where she must return? That guides the sleek gray fish and the badly wounded Steve Romano to seek refuge in the Sea of Cortez? That fuels William Henry Stitt and his great grandson in their unending quest for knowledge? WHAT IS THE FORCE?