I found this in the 1910 GE Railway Supplies catalog. The insulator on the left is the scarce Thomas U-615A or the earlier rare U-616. The insulator on the right is the rare GE breakaway insulator, M-2202. It was made based on the 1909 Charles Eveleth patent (see link below). It has "weakening grooves" across the top of the skirt to aid in pieces breaking off when struck by rocks or bullets. The intent was to protect the insulator so only minor damage would result from such vandalism instead of damaging the insulator to such great extent that the insulator would lose its ability to protect the conductor. The larger version, M-2505, was not shown. These insulators were made by the Lima Insulator Co. and are quite rare.

http://reference.insulators.info/patents/detail/?patent=U917031