From the Star Wars novelization published in 1977 :

"They're coming through!" Luke groaned. The Princess turned carefully to stare across the gap. "This must be a single- unit bridge, with the controls only on the other side." Reaching up to the point at the panel holding the unreachable controls, Luke's hand caught on something at his waist. A frustrated glance downward revealed the cause¡ªand engendered a bit of practical insanity. The cable coiled tightly in small loops was thin and fragile seeming, but it was general military-issue line and would have supported Chewbacca's weight easily. It certainly ought to hold Leia and himself. Pulling the cable free of the waist catch, he gauged its length, matching it against the width of the abyss. This should span the distance with plenty to spare. "What now?" the Princess inquired curiously. Luke didn't reply. Instead, he removed a small but heavy power unit from the utility belt of his armor and tied one end of the cable around it. Making sure the wrapping was secure; he stepped as close to the edge of their uncertain perch as he dared. Whirling the weighted end of the cord in increasing circles, he let it arc across the gorge. It stuck an outcropping of cylindrical conduits on the other side and fell downward. With forced patience he pulled the loose line back in, then recoiled it for another try.