Light bulb continually goes out?

I have 4 outside 110v a/c lights installed in cement posts. They are all on the same circuit. Each runs from an outside plug to the individual light. The bulb in the last one in the series keeps going out after about 1/2 hour. This baffles me; I have changed the socket but it still happens. What would make a bulb continually go out after 1/2 hour? Obviously there is no surge because the others don't go out. Could the wire in the cement post have a slight short %26amp; is heating up and this causes the bulb to go out?

Light bulb continually goes out?
you have a couple of possibilities.1. You could have a short but this is not what i think it is. I believe that if these lights are wired in series that the power that is reaching the last light is not enough of consistant. Try only putting in the last light and see if it still goes out. If it does than it is wiring but if not i think there must be too many lights off of one wire.
Reply:Try a 130-volt bulb. I had this happen too. It's bizarre but if you use a bulb with a higher VOLTAGE (not wattage) it should work.