A friend found these four chair-leg insulators several years ago here in California on a hillside near a mountain fire lookout tower. The solid glass chair legs are embossed: C.F Birtman & Co. Cemented to the ends of the clear glass legs are aqua CD 106 patent dated Hemingray 9's! The aqua Hemi's display no sign of wire rub, indicating the insulators were not used second-hand for this purpose. Why were they added to the clear glass legs? The most logical reason would be for added chair height, but your opinion is welcomed. The wear marks on the domes of the Hemi's are quite minimal, exhibiting a circular frosted area with very little worn away glass. This could indicate limited use on a chair before it was discarded; a soft wooden floor; or there's the possibility that they were not used on a chair at all--maybe a table?
(Note: The clear leg portion is known to be part of a table used for a medical apparatus, but other information indicates they held a secondary use for insulating chairs, etc.)