Small part below of a very long article/lecture series.
http://www.fau.edu/divdept/physics/pw/jordanrg/LLS/lecture14/LLS_lecture_14.htm - Chapter 14 The Atmosphere
Actually it looks pretty intersting I think I’ll read the whole thing.
"In 1794 Benjamin Franklin wrote the following, in a letter to Gentleman’s Magazine that was published in May 1750:
“There is something however in the experiments of points, sending off or drawing on the electrical fire … I am of the opinion that houses, ships and even towers and churches may be eventually secured from the strokes of lightning by their means; for if instead of the round balls of wood or metal which are commonly placed on the tops of weathercocks, vanes, or spindles of churches, spires or masts, there should be a rod of iron eight or ten feet in length, sharpened gradually to a point like a needle, and gilt to prevent rusting, or divided into a number of points, which would be better, the electrical fire would, I think, be drawn out of a cloud silently, before it could come near enough to strike.”
Initially, Franklin believed that lightning rods discharge clouds. However, they do not; the charge that flows normally between a lightning rod and a thundercloud is much too small to discharge the cloud. Rather, lightning rods serve to route the current in a lightning strike harmlessly to the ground by diverting it through a very low resistance path as Franklin realized in 1755. Lightning rods were first used for protection in 1752 in France and later that year in the U.S. So, how do lightning rods work? The rod actually diverts the stroke towards itself only at the final stage of the downward path of the leader, see figure 43. As we saw earlier, when the leader is a few 10’s of meters from the ground, its large negative charge attracts large amounts of positive charge on the Earth near it and especially on sharp objects like lightning rods that are ‘well-grounded’. An upward traveling discharge is initiated from the very high density of positive charges on the end of the lightning rod, and when the two leaders connect the cloud is now ‘wired’ to the ground through the lightning rod, rather than the house, or tree, etc.
Any high object can initiate an upward moving discharge; it is important that the lightning rod be the highest object near the structure to be protected. A single rod will almost certainly protect a single building if it is tall enough, see figure 44, although to protect larger buildings several strategically placed rods would likely prove more practicable. However, no lightning rod can offer complete protection; for example, the Empire State Building was struck at a point 50 feet below the top! It is also common practice to protect overhead high voltage transmission lines from lightning strikes by stringing a well-grounded wire above the lines to intercept strikes that would otherwise have hit the power lines."