Understanding how a lightning rod works requires a significant amount of scientific education. Bradbury was a highly educated man, but he was also very aware of how small-town folks lived and how they viewed the world.

To most people, a simple lightning rod is a baffling, counter-intuitive device. I can protect my house from lightning by drawing lightning toward my house with a long metal rod? On the surface, it doesn't make sense.

Lightning rods are the closest thing modern man has to the talismans of old; both are incomprehensible, and are said to protect a person or property against seemingly supernatural injury.

But there's another layer to this. In the beginning of Something Wicked This Way Comes, the main characters receive a lightning rod from a passing salesman. They, for free, receive protection from an oncoming storm which, despite all of the primal fear it inspires, is an entirely natural phenomenon.

However, they received no such protection from the supernatural, mystical evils that are about the inhabit the town. The implication is that, despite our understanding of the natural world, human beings can never truly know, or protect themselves from, supernatural evil.