Reverend William Hayden, an Englishman just three months a priest, was in front of McKeon and tilting toward the ruby glow of the sanctuary light in order to read his breviary.
Once the light enters the ruby, its speed is slowed down to around the speed of sound (approximately 741mph) and the spinning motion of the rod drags the light with it, resulting in the image being rotated by almost five degrees: large enough to see with the naked eye.