Click on the applet and press "y" (and... be patient!!) to add a refracting sphere.
Press "n" to remove the lens (and again, be patient).
Press "1","2","3" or "4" to put the refractive index to the corresponding value.
Press "0" to put it to 1.33 (the value for water).
Press "f","b","l","r" to make the sphere move forward, backward, left or right.
Source code
inside.java Light.java material.java sphere.java Surface.java Plane.java Polyhedron.java Ray.java Vector.java