And a mistake in the original ray tracing paper

More fun trivia on the original ray tracing paper.  Whitted put in attenuation with distance along the reflection rays:

This is a very understandable mistake.  First, that radiance doesn't fall off as distance squared is confusing when you first hit a graphics class, and there were no graphics classes with ideal specular reflection then; Whitted was inventing it!  Second, the picture with the bug I think probably looks better than without: the fading checkerboard in the specular reflection looks kind of like a brushed metal effect.  So it's a good hack!

Whitted's famous ray tracing image.  From wikipedia

There are two lessons to draw from this: when bugs look good think about how to make them into a technique.  Second, when you make a mistake in print, don't worry about it: if somebody is pointing it out decades later you probably wrote one of the best papers of all time.  And if the paper is not great, it will disappear and nobody will notice the mistake!