Parlor tricks based on electricity were all the rage in mid-18th-century Europe. One of the most famous demonstrations, popularized by the electricity pioneer Stephen Gray, was the “Flying Boy" [PDF], which featured a young boy suspended from the ceiling by silk ropes. Thus insulated from the ground, he was subjected to an electrical charge and then was able to do apparent magic, such as turning the pages of a book just by passing his hands over them. The grand finale had a noninsulated audience member touch the boy's nose to create a spark and shock. History is silent on how the boy felt about this painful turn of events.
U.S. founding father Benjamin Franklin wanted to understand the phenomenon behind these clever tricks. Along with Ebenezer Kinnersley, Thomas Hopkinson, and Philip Syng Jr., he undertook a systematic investigation into electricity. Peter Collinson, a fellow of the Royal Society, in London, provided some of their instruments.
Boy Toy: In the “Flying Boy" demonstration of electricity, popular in the mid–18th century, a boy is suspended by rope from the ceiling, an electric charge is applied, and the boy then performs feats of apparent magic, like turning the pages of a book by just passing his hand over them.Image: Interfoto/Alamy
Starting in 1746, the group conducted a series of experiments in Philadelphia, which Franklin described in letters to Collinson. Collinson read the reports to the Royal Society, and then published the letters in an 86-page pamphlet that was quickly translated into French, German, and Italian. Franklin introduced the terms plus and minus and positive and negative to describe electrical states and charging and discharging to describe the actions of a Leyden jar, which was essentially a capacitor that stored charge for later use.
Electricians, as some early experimenters called themselves, charged a Leyden jar using machines such as the one pictured below. A user rotated the glass plate, which built up static electricity as it rubbed against the leather pads. The electricity was then drawn off by conductors (missing on this machine) to the Leyden jar.
Capacitance was measured by the number of Leyden jars, but the jars varied in size and the thickness of the glass, so this was not a precise measurement. It would be anachronistic to apply modern units of measurement to the early experimenters' jars—such units had not yet been invented or standardized, and the mathematical relationships of energy, capacitance, and voltage difference had not yet been discovered. But according to one modern source, a typical pint-size Leyden jar (roughly half a liter) would likely have had a capacitance of about 1 nanofarad and the energy of about 1 joule.
Spinning Wheel: To charge a Leyden jar, the user would rotate the glass plate. Friction between the glass and the leather pads produced static electricity, which was then stored in the Leyden jar.Photo: American Philosophical Society
Franklin also constructed an electrical battery by linking Leyden jars together in parallel, such as the one shown at top, which Joseph Hopkinson, Thomas's son, donated to the American Philosophical Society in 1836. The battery's 35 jars increased the amount of electricity Franklin could use in an experiment.
Franklin's fascination with electricity spilled over to more elaborate parlor tricks. In the summer of 1749 he hosted an electrical feast, which began with Franklin electrocuting a turkey and then roasting it on a spit that was turned by an electrically powered jack. Guests sipped wine from electrically charged glasses, which gave a small shock when brought to the lips. He invented a game called Treason, which featured an electrified portrait of the King of England wearing a removable gilt crown. Players got shocked if they were holding the frame while they attempted to steal the crown.
Franklin's experiments occasionally went awry. In some of his first attempts at turkey electrocution, the birds were merely stunned, arising a few minutes later after regaining consciousness. In his third letter to Collinson, Franklin noted the importance of grounding when charging and discharging the jars—a lesson he'd learned the hard way. On one memorable occasion, he electrocuted himself instead of the bird. Witnesses to the event claimed to have seen a great spark and heard a loud crack similar to the sound of a pistol.
The Body Electric: Franklin's investigation of electricity proved nearly fatal when he attempted to electrocute a turkey for Christmas dinner and shocked himself instead.Image: GraphicaArtis/Getty Images
In a letter dated 25 December 1750, Franklin described the unfortunate episode: “I have lately made an experiment in electricity that I desire never to repeat. Two nights ago, being about to kill a Turkey by the Shock from two large Glass Jars, containing as much electrical fire as forty common Phials, I inadvertently took the whole thro' my own Arms & Body, by receiving the fire from the united Top Wires with one hand, while the other held a chain connected with the outsides of both Jars."
Although Franklin never lost consciousness, his arm tingled with numbness for the remainder of the evening, and his chest felt sore for the next few days.
He pleaded with the letter's recipient—presumably his brother John—not to spread the story. “Do not make it mor Publick, for I am Ashamed to have been Guilty of so Notorious A Blunder." Franklin did give permission to relate the cautionary tale to James Bowdoin II, a fellow experimenter in electricity. Bowdoin not only read the letter but made a copy of it. And thanks to the digitized version of that copy available from the Massachusetts Historical Society, we can all share a laugh at Franklin's expense.
Despite this blunder, Franklin continued his explorations in pursuit of a practical use for electricity. In particular, he theorized that electricity could be used to tenderize meat. By 1773 Franklin had not only a hypothesis but specific instructions.
In a letter to Jacques Barbeu-Dubourg and Thomas-François Dalibard, Franklin explained his theory by comparing it to a tree being struck by lightning. Just as lightning vaporizes the moisture contained in a tree, separating the fibers into fine splinters, so too could electricity forcibly separate the particles of meat to make them tender.
Franklin recommended a battery of six large glass Leyden jars to electrocute and tenderize a 10-pound turkey or a lamb. Each jar held 20 to 24 pints (9 to 11 liters). Having learned from his own mistakes, he ended his letter with a warning: “The one who does the operation must be very aware, lest it happen to him, accidentally or inadvertently, to mortify his own flesh instead of that of his hen."
More than 200 years later, researchers continued to investigate how electrical stimulation could be used to tenderize meat. A 1981 review of the field by S.C. Seideman and H.R. Cross of the U.S. Department of Agriculture cited dozens of contemporary studies on the theory and mechanics of electricity as a meat tenderizer.
Compared with practices in Franklin's day, the modern field of animal science is much more sophisticated. Experts have devised, for instance, specific measurements of meat tenderness, in kilograms of force needed for a steel blade to slice through the core of cooked meat. Meat requiring less than 4.6 kilograms to cut is reliably tender, while that requiring more force is deemed chewy and unpalatable.
By rendering tough cuts of meat more tender, electrical stimulation allows more of the animal to be used. It's also potentially cheaper to electrically tenderize meat than to tenderize it by aging it in a refrigerator for several weeks. Still, electricity changes the color and moisture of meat in ways that are considered undesirable.
A 2008 episode of “MythBusters," a TV show that applied science to try to prove (or disprove) urban legends and physics-defying Hollywood stunts, tackled the topic of tenderizing steak by use of explosives:
Spoiler alert: Exploded meat is more tender than the unexploded kind.
While the concept may have been new to TV viewers, the meat industry had been experimenting with it for years. As early as 1970, Charles S. Godfrey obtained a patent for tenderizing meat by submerging it in water, detonating an explosive, and having the shockwaves reverberate through the meat. The idea was that the water content of the meat would vibrate and break apart the tiny fibers of muscle, surprisingly similar to Ben Franklin's original theory for tenderization.
In 1999, John B. Long, an explosives expert who had retired from Lawrence Livermore National Laboratory, improved on Godfrey's idea, patenting a method that he called the Hydrodyne process. Sadly for meat lovers, Hydrodyning didn't scale, and exploded steak still isn't on offer at your local butcher shop or supermarket.
Will electrotechnology ever yield a brisket as tender as a tenderloin? A 2014 review published in the Asian-Australasian Journal of Animal Sciences concludes that “despite extensive research on [electrical stimulation], the fundamental mechanisms and the appropriate commercial applications remained obscured." Remarkably, the paper cites Benjamin Franklin's early experiments. Franklin's quest for tender meat goes on.
An abridged version of this article appears in the December 2018 print issue as “Electricity as Turkey Tenderizer."
Part of a continuing serieslooking at photographs of historical artifacts that embrace the boundless potential of technology.
A correction to this article was made on 19 February 2019.