An old Hemingray power insulator, big and heavy, round dome, wider than tall.  It's marked No. 71, High Voltage, Patented May 2, 1893. It was in use from 1893 - 1930s.

It's 3 3/4" tall, 4 5/8" wide, glossy body. About 3 drip points are missing, a couple of others are sharp. There's a glass bruise near the bottom. It weighs 2 lb-6 oz.

I also have a purple California CD-161 insulator for sale in an auction.