Hi debook!
I'm guessing that perhaps...
The wire running along (or into?) the glass rod, seems to be a continuity element for the case in which the whole structure was fitted into an one-side based bulb.
As you knows, tubular lamps are made not only in the "sofito" or "sofitten" way with two caps at each end, but with Edison cap one-side ended. In such cases, the "distant" end of the filament could be connected by means of a fine wire that runs through the glass rod, allowing the use of the same type of structure for both lamp styles, simplifying the manufacturing jobs.
About bulb-style ballast lamps, they were very common in various applications, such as fluorescent tubes ballasting (using the "trash" radiated light as in blended lamps to increase the total emitted flux), in radio receivers among the other tubes, in battery chargers and rectifiers as absorption resistances...
In any cases, it's easier and safer to have the resistive elements enclosed into a glass envelope, so for many applications, these were manufactured in bulb way instead open-air resistive wires.
Also, the bulb can be filled with inert gases that allows the heat conduction and convection instead the air that could oxidize and deteriorate the constitutive metals of the elements.
If you remember, in Nernst lamps the ballasting and regulation of the current through the ceramic luminous rods was done by means of iron resistive wires into a glass envelope filled with an hydrogen atmosphere.
The same principle was employed in some universal (AC/DC) radio receivers to regulate the inrush and regime power, by means of the well known "Amperite" or "Ferro-hydrogen" regulator tubes.
Best regards,
M. Gonz?lez.
http://mis-bombillas.webcindario.com[This message has been edited by M?nico Gonz?lez (edited June 21, 2004).]
