[hellbender]

OK, I’m being picky, but here goes: First, the Leyden jar was a form of capacitor, not a battery. Second, I doubt that a silk thread would insulate you from lightning. With enough voltage, electricity can travel through things not normally considered good conductors.

[Bobalu]

A capacitor is a type of battery.

[Congressman Billybob]

Franklin's write up of his own experiment noted that he was careful to keep the silk insulator dry, whereas the kite and string were thoroughly wet.

John

[HiTech RedNeck]

The first thing to break down would not be the silk, but the air. Franklin was still pretty lucky. The key was close enough to draw an arc to his knuckles when he reached out.