I love vintage & antique lockets! When I stumble across one at a flea market or estate sale I usually end up buying it. As jewelry, they are often intricate & beautiful and as nostalgic objects, they are both mysterious & romantic. I wonder what torrid love affairs the wearer had or unrequited loves they may have harbored. Lockets seem like they have secrets already inside.
This particular locket came with a mystery--a trademark that eventually lead me to its history. I was able to track down information about W & H thanks to the New York Public Library's digital archives of advertisements and a few skilled Ebay auctioneers.
The trademark inside this locket, "W & H Co" (pictured below as 1) with a heart etched around it (pictured below as 2), belonged to Wightman & Hough Company who operated out of Providence, Rhode Island.
Wightman & Hough Company made sweetheart necklaces from 1856 until 1922. They were primarily renowned for their lockets. Their slogan, which I find to be quite amusing & sweet, was "There's a heart in every locket!" How true! Below are 3 of their advertisements: 
Though I do not know the exact date of this locket as of yet (sadly, I must wait a long while for an inter-library loan to come through for a jewelry catalog from 1910 to verify thestyle & date of this locket)--I believe it is from the latter period of W & H Co.'s production. The design on the locket is an Art Deco pattern and the stones (which are all in tact) are sapphires which were popular at that time. 
For now I know the approximate value of the locket is between $65.00-$250.00 (I paid $12.00 which makes me feel a bit like a Robber Baron). You never know what you will find & what it is worth until you do a little digging--sometimes you've gotta trust your gut! Happy Flea Marketing everyone!