It has been awhile since I have seen lightening rods on a barn.
If you were a farmer, those lightening rods could save your barn from a lightening strike that could cause a fire in your hay mow. The glass balls would break if the building was hit by lightening. The lightening would be directed downward following a wire into the ground and the barn would be saved.
Years ago when many people lived on farms, this was one way that they could protect their animals and hay crop..without the barn and its full hay mow..they had nothing and no way to eke out a living.
Not too many barns around these parts anymore..one by one they are falling down. They are expensive to maintain and repair. I will take their photos while I can:)