"I Flamed Amazement": The Physics of St. Elmo's Fire

Clad in a bright yellow raincoat and a crown of butterflies, laughing and singing, Ariel delighted the audience from the first moments of California Shakespeare Theater's "The Tempest."

I always love productions at the open-air Bruns Memorial Theater, but the airy sprites of Shakespeare's last full play seem particularly well-suited to the natural environment. Orinda's eucalyptus groves and rolling golden hills could as easily populate Prospero's remote island as do the characters of kings and dukes, clowns and cannibals.

Of all the characters, though, Ariel was "an easy favorite" in the words of my father-in-law. Played by choreographer Erika Chong Shuch, her movements overflowed with emotion and expression. It was easy to believe in her magic.

I boarded the king's ship; now on the beak,
Now in the waist, the deck, in every cabin,
I flamed amazement: sometime I'd divide,
And burn in many places; on the topmast,
The yards and bowsprit, would I flame distinctly,
Then meet and join.

--Ariel, The Tempest (Act I, Scene 2), William Shakespeare

For the beleaguered sailors, Ariel personified St. Elmo's Fire, the glow that can appear around ship masts and chimneys during a thunderstorm. Lacking a scientific explanation for the light, people in Shakespeare's time attributed it to the patron saint of sailors.

Four hundred years later, we still don't completely understand how storms create such magnificent atmospheric phenomena. But we understand a great deal more than we once did.

It starts with storm clouds, which are positively charged on top and negatively charged on the bottom. The reason for this charge differential has to do with turbulence inside the cloud, exact details TBD. The negative charge at the bottom of the cloud is so strong it pushes away electrons in the earth's surface, leaving a positive charge in the ground, in trees, in chimneys and ship masts.

When some object on earth's surface accumulates enough positive charge, it ionizes the air around it, pulling molecules apart into their constituent positive and negative charges. An ionized gas, or plasma, has no overall charge, since it contains equal numbers of positive and negative ions, but it is an excellent electrical conductor. And it glows. It's beautiful, and a little creepy, but it's not dangerous like lightning.

In the Grove Talk before the show, CalShakes resident dramaturg Philippa Kelly emphasized the unpredictable perils of Shakespeare's time. Fires especially were ubiquitous, necessary for daily work, yet often raged out of control--as in the destruction of the Globe Theater. Ariel's magic is the magic of St. Elmo: a safe fire that serves its master's interests and causes no damage. Today, we've harnessed the same plasma phenomenon to build neon signs and modern TVs that are incapable of burning down a building. An instance, perhaps, of Arthur C. Clarke's Third Law?

"Any sufficiently advanced technology is indistinguishable from magic."