The glass is a non-conductor, and prevents the lightning from leaving the rod.
Why is it not safe to stand near a fire during a thunder-storm?
Because the fire is a good conductor, and sometimes draws the electricity into the room.
What part of the room is the safest place?
The middle of a room is thought to be the safest place.
Is a feather-bed a safe place?
Yes; because the feathers are a non-conductor, and will not attract the lightning.
Is dry air a non-conductor of electricity?
Yes; dry air is a non-conductor of electricity.
When are thunder-storms most frequent?