It sounds like the object you’re describing above the basement door in your 1890s home is likely a pilot light or indicator light. Here’s a breakdown of some common interpretations based on people’s opinions:

• Pilot Light/Indicator Light: Many people, like Roxane and Michael, suggest it’s a light that turns on to indicate the basement light or another electrical device (like a sump pump) is running. This was especially useful in older homes to remind people if something was left on, like a basement light.
• Power Indicator: Some comments (like Ed’s) suggest that this light shows if the outlet is powered or “hot,” a useful feature in older electrical systems.
• Night Light or Utility Light: Several people, including Lindy and Nicole, think it might have been used as a low-wattage light to guide people in the dark, illuminating the area around the door or another switch.
• Old-fashioned Electrical Outlet: Although the dome has a small bulb in it, the outlet beneath could also have been used for sump pumps or other equipment.

The object you have could be a combination of a plug with a built-in indicator light, quite common in older homes. Over time, these kinds of outlets were often painted over, which makes them harder to identify today.

If it’s still wired up, it might be worth consulting with an electrician to ensure it’s safe, as older wiring can sometimes be a safety hazard, as Cyndi mentioned.