A lot of older houses had lightning rods on their roofs. Particularly
farm houses. They would have a thick braided cable that went to ground
rods. Many of them had a glass ball in the center of the copper rod.

I'm wondering of they really did any good. Sure, you want to ground a
strike, but on some ways, it would seem to me that they also could
attract lightning. Anything that is a high point in an area attracts
it, such as large trees. Of course metal attracts, so putting a metal
rod on a roof is an attractant. In a direct strike, I doubt they would
do anything, in fact they might get hot enough to start a fire. But a
discharge nearby could be sent to ground via the lightning rods.

One other thing, was there any usefulness to the glass balls in the
middle, or were they strictly decorations?