HV Resistors

In my never ending quest for components, I have come across some unusual 
resistors.  These resistors were originally in a 30 KV DC power supply. 
 They are 40 Megaohms( or was it 400) in value.  They were about 1/2" in 
diameter by 8" long.  I regret I didn't get them when I found them.  Can 
anyone think of a purpose that we might use these for?

Scott Myers