PHILADELPHIA (REUTERS).- If it’s hard to grasp the genius of Leonardo da Vinci, it may be because he left no working models of the drawings that showed his intimate grasp of fields ranging from engineering to botany and anatomy. But Philadelphia’s Franklin Institute is hosting an exhibition that explains his paintings and the construction and operation of his famous inventions using newly created models as well as dazzling touch-screen technology. “Leonardo da Vinci’s Workshop,” which runs from Saturday until May 22, examines his flying machines, weapons of war, robots and other mechanical devices by using computer graphics to create three-dimensional pictures of the items that in their original form are represented only by drawings in the artist notebooks. “The genius of Leonardo da Vinci, the greatest mind of the Renaissance, springs to life in this much heralded exhibit from Italy,” the institute said on its website. It added