A change in a ca. 270 y old protection device |

I’m sure y’all remember this tidbit. We must have learned it in second grade. That Ben Franklin, on a June afternoon in 1752, thought it would be the perfect time to go fly a kite. While everyone else was scurrying to their homes.

Franklin expected to prove that lightning was an electrical event. (He also wanted to protect folks from the violent nature of lightning, for which this experiment would be crucial.) Which meant he needed to wait for a thunderstorm to encounter lightning. His materials- a kite, silk handkerchief, hemp string, silk string, a piece of wire, a house key, and a Leyden jar (this was used to store the electrical charge). Franklin had discussed this idea with Joseph Priestly (who discovered oxygen), and they determined that flying a kite would be much easier than trying to stand atop a church spire to effect the experiment.

Now, here’s the rest of the story. Ben didn’t discover electricity in the lightning that day. Or, really ever. And, Franklin was darn lucky that lightning didn’t strike his kite. Or, he would have been electrocuted.

But, Franklin’s Leyden Jar concept did acquire ambient electrical charge from the storm. That piece of wire served as a lightning rod, the wet hemp conducted the electrical charge, the silk string (which was dry) did not. The key- once Franklin approached it with his hand (he noticed that the hemp threads were standing erect)- picked up the positive charges in his hand and the metal key became negatively charged. The Leyden jar collected “electric fire very copiously”.

Franklin waited about 4 months to report this experiment (Pennsylvania Gazette, 19 October 1752). And, this is why Franklin was awarded the Copley Medal from the Royal Society. And, it is how Franklin developed his Lightning Rod concept. (See picture above.) His description led to an iron rod- somewhere between 8 and 10 feet long, sharpened to a point at one end. And, believe it or not, this has been our protection against lightning for some 275 years or so. (We have since learned that the protection radius of a lightning rod is about the same as the length of the rod.)

Santis Mountain — SantisMountain (see the communications tower?)

To protect larger areas and structures (in particular, we seek methods to protect our launchpads and airports), something else is needed. And, now a bunch of scientists in Europe may have done just that. The experiments were effected on Santis Mountain (in northeast Switzerland), atop a 407 foot [124 m] communications tower that is routinely hit by lightning about 100 times a year. And, the scientists induced lightning to appear, as well. Using a vehicle-sized device powering a rapid fire laser (Yb:YAG laser emitting pulses of picosecond duration and 500 mJ energy at a wavelength of 1,030 nm and at 1 kHz repetition rate) next to the tower, both a beam of light (to serve as the ‘lightning rod) and a channel of thinned out air that attracted lightning developed.

Drs. A Howard, P Walch, V Moreno, B Mahieu, M Lozano, L Bizet, F Rachidi and A Mysyrowicz (Ecole Polytechnique, Palaiseau, France); Dr. T Produit (A*STAR, Singapore); Drs. A Sunjera and A Mostajabi (Ecole Polytechnique, Lausanne, Switzerland); Drs. C Herkommer, K Michel, and T Metzger (TRUMPFF Scientific Lasers gmBH, Unterfohring, Germany); Dr. Y-B Andre, MC Schroder, G Schimmel, M Moret, J Kasparian, and J-P Wolf (University of Geneva, Switzerland); Drs. M Stanley and WA Rison (New Mexico Institue of Mining and Technology); Dr. O Maurice and B Esmiller (Ariane Group, Les Mureaux, France); Dr. W Haas (Swisscom Broadcast AG, Bern, Switzerland); Dr M Rubinstein (University of Applied Sciences and Arts Western Switzerland); and Dr. V Cooray (Uppsala Univerity, Sweden) published the results of this study in Nature (“Laser-Guided Lightning”).

As you can see from graphs A and B, while not yet perfected, these experiments prove that lasers can divert lightning- and well above the radius of what Franklin’s lightning road can produce.