· Ben Franklin at 300 — Our Colonial PowerPoint Man ·
I hear Philadelphia is powering up "Benergy" this year, and on Benjamin's Franklin's birthday, it's good to draw on it. Though Boston may still claim his birth, Philly, of course, owns his work. Indeed, think libraries, fire houses, nations, universities, post offices — even humble lightning rods.
Did I say humble? Alas, only advisedly! For if you conduct Old Ben's virtue to ground in Quaker Philadelphia, you'll understand still another point: "Benergy" is only an electrifying figure for something more methodically stylish.
In the fifth letter, Franklin described how discharges between smooth or blunt conductors occur with a "Stroke and Crack," whereas sharp points discharge silently and produce large effects at greater distances. He then introduced what he viewed to be a "Law of Electricity, That Points as they are more or less acute, both draw on and throw off the electrical fluid with more or less Power, and at greater or less Distances, and in larger or smaller Quantities in the same Time." Given his interest in lightning and the effects of metallic points, it was a short step to the lightning rod:
I say, if these Things are so, may not the Knowledge of this Power of Points be of Use to Mankind; in preserving Houses, Churches, Ships, etc. from the Stroke of Lightning; by Directing us to fix on the highest Parts of those Edifices upright Rods of Iron, made sharp as a Needle and gilt to prevent Rusting, and from the Foot of those Rods a Wire down the outside of the Building into the Ground; or down round one of the Shrouds of a Ship and down her Side, till it reaches the Water? Would not these pointed Rods probably draw the Electrical Fire silently out of a Cloud before it came nigh enough to strike, and thereby secure us from that most sudden and terrible Mischief!
Clearly, Franklin supposed that silent discharges from one or more sharp points might reduce or eliminate the electricity in the clouds above and thereby reduce or eliminate the chances of the structure being struck by lightning. From his earlier observations, he knew that point discharges work best when the conductor is grounded and that lightning tends to strike tall objects. Therefore, even if the point discharges did not neutralize the cloud, a tall conductor would provide a preferred place for the lightning to strike, and the grounded conductor would provide a safe path for the lightning current to flow into the ground.