I think I know just the thing you are talking about. The house I grew up in during the 60's had just such a light centered over the kitchen table. We kept it at the upper height when the table was not in use and pulled the light down closer to the table during meals.
It had an egg-shaped bulbous thingy in the middle of the vertical line. My guess is that the cord wrapped around a spool in the inside of that egg shape, much like a fishing reel. It had some sort of internal locking spring mechanism that kept it at a certain height until you decided to adjust it. As the light aged, the spring mechanism got worn out and the lamp would gradually lower itself on its own until it became a nusance.
I bet Lightwizard would know exactly what you are talking about.