On the plausibility of Superman's x-ray vision

Requirements that a vision system must meet to make Superman 's x-ray vision possible are stated, and two solutions are proposed. In one, emitted x-rays carry the information to Superman 's eyes; in the other, emitted rays make objects transparent to a second type of ray. Further subjects lending themselves to this type of research are superhearing , the biomechanics of leaping tall buildings, or being faster than a bullet.