No refraction in Leonardo's orb

摘要

Martin Kemp suggests that Leonardo da Vinci's knowledge of optics and minerals is evident in the representation of the orb in the Salvator Mundi painting (Nature 479,174-175; 2011). But I question his interpretation that the double contour of the heel of the hand holding the orb depicts the birefringence (double refraction) arising in a calcite orb.