PixHound wrote:
Yes, refraction is correct...but my thought was that the focal point of the sun through a glass sphere would be so close to the sphere, that the crystal ball must have actually been on the couch, and not in a stand of any kind. This is illustrated by the plastic ball I placed in the sun on my shop floor. The focal point is well under the radius of the ball.
When I was a kid I had a glass sphere like that. We set it on a piece of paper in the sun, it would catch the paper on fire. Lots of fun! Ants and caterpillars did not like it.