 The sphere moves on its base a 1/4 to a 1/2 inch every year, as measured by the distance traveled by the unpolished spot from where it was mated to the pedestal.While the movement of the sphere is thought to be facilitated by freeze-thaw cycles, earth tremors, or trapped air or water under the base, there has been no conclusive explanation for patterns that the sphere seems to follow.The movements of the sphere have been documented by numerous news outlets and it has been featured in Ripley's Believe it or Not (September 29, 1927).