I am sure you are all aware of this, but just in case you are not, I ran across a wonderful site on early lighting and light sockets.
It is antiquesockets.com. These are two links to lighting of the 1880's on the left menu, down a considerable distance from the top--
one is called "Styles 1881 to 1884" and the other is "Other pre-1888 Styles." There are fascinating photos, catalog illustrations and other info about later, turn of the 20th century lighting as well. Using another part of the site, I was able to date a lamp base with Hubbell sockets and acorn pulls to 1904-1909 (a Saturday sale purchase--the base turns out to be a Pittsburgh base.)