This is the AR-1 Argon light bulb, a glow bulb produced by General Electric. They were used in argon printers and in some science experiment kits, and were also sold to be used as night lights and safety lights for exits and alarms. And although they are no longer being made, they can still be found on eBay with a little searching. The identical W1A bulb is simply a renamed AR-1 bulb.
This bulb seems to produce a lot more "blacklight" than more modern fluorescent and incandescent blacklight bulbs. This bulb is hard to find with the electrodes in perfect shape (most of the time they are bent up, forming a semi-flat "V"). There is a similar version of this bulb that is filled with neon gas instead, which is called the NE-34 and glows with a yellowish-orange hue. For more info on this bulb, check out the related links below.