I saw an experiment the other day, where a van de graaf generator charges up this big smooth chrome sphere. There is a "wand" with a much smaller sphere nearby that's grounded, and periodically a spark can be heard and seen when the big sphere dischrages to the wand, which corresponds to dielectric breakdown. What is intereresting is that when another pointy metalic wand (also ground) is brought near the van de graaf's big sphere, no more sparks anywhere can be seen anymore. So my theory is that the discharge is going through the pointy wand. But why isn't there a spark to discharge through the pointy wand? doesn't dielectric break down needs to happen to discharge through the pointy wand?