Benjamin Franklin’s 9 Most Ingenious (and Zany) Inventions

Franklin’s most famous invention, the lightning rod, was born from his experiments with electricity in the late 1740s. An early description of his idea to protect buildings and ships from “electrical fire” appeared in a 1750 letter to Peter Collinson of The Royal Society in London, but it wasn’t until the 1752 demonstrations of lightning’s electrical qualities—first in France, then with Franklin’s kite experiment—that the first lightning rods were installed in Philadelphia. Franklin soon offered a more detailed explanation of this safety device—one iron rod on a roof, another planted in the ground and a brass wire to funnel the electrical charge downward—in the 1753 issue of Poor Richard’s Almanack.

“Franklin received feedback from his friends in the area who installed lightning rods on their homes, as well as from correspondents in other states,” Carroll says. “[He] suggested improvements based on the feedback like increasing the size of the lightning rod so it would withstand multiple impacts from lightning strikes.”

Centuries after Leonardo da Vinci suggested something similar, 11-year-old Franklin devised the first working swim fins: a pair of “oval paddles, each about 10 inches long and 6 inches wide, with a hole for the thumb, so I could hold them against the palm of my hand.” Although the fins helped him swim faster, the inventor complained that they “fatigued” his wrists and his attempt at fins for his feet didn’t work particularly well.

On the other hand, he enjoyed the “greatest pleasure imaginable” when he discovered he could be pulled across a pond by a kite on a string—a precursor to today’s kitesurfing. It was because of these innovations and his lifelong promotion and enthusiasm for aquatic activity that Franklin was inducted into the International Swimming Hall of Fame in 1968.

Sometime before 1758, Franklin designed a 12-hour clock that was mechanically simpler than other options of the period. Backed by an interlocking mechanism of three wheels and two pinions, the clock featured two dials: The smaller one counted off seconds, while the larger one displayed hours and minutes in a four-quadrant design. Instead of each hour getting its own position on the clockface, four groups of hour numbers were stacked and aligned to the cardinal directions. Each quadrant then featured 60 minute markings along the face’s circumference. Although Franklin later claimed to have seen versions of his clock in Paris, he never published his own account of this invention. The lone description of this timepiece comes from a 1773 publication by James Ferguson, who noted that the clock “measures time exceedingly well.”

As far back as the late 1730s, Franklin began developing an iron fireplace intended to conserve wood and heat homes more effectively. The first iteration of what he called the “Pennsylvania Fire-Place” was built with an air box, a baffled chamber behind the fire which drew in smoke-free air from below that was heated as it rose before being expelled through vents. Additionally, a U-shaped siphon funneled smoke over the air box, under the back of the stove then up the chimney. Although Pennsylvania Deputy Governor George Thomas was impressed with the creation, Franklin’s stove didn’t perform as effectively as he hoped, and the inventor attempted to improve on the design for much of the rest of his life.

“Though his original design wasn’t effective in removing smoke, it did require less wood and was less dangerous for residents,” Carroll explains. “Most people refer to the Pennsylvania Fire-Place as the ‘Franklin Stove’ even though others continued to make improvements on it.”

In 1768, Franklin unveiled what he described as an attempt to “give the alphabet a more natural order.” Explaining that each letter should only be associated with one sound, he did away with six he considered superfluous: C, J, Q, W, X and Y. Franklin also introduced six new letters, including those that represented the sounds of “sh,” “ng” and “um.” Despite the zeal he showed for his alphabet in correspondence from that period, Franklin seemingly lost interest shortly afterward, and the system never gained traction despite being endorsed by lexicographer and dictionary namesake Noah Webster two decades later.

Seeking to aid his kidney stone-stricken brother John, in 1752, Franklin devised a catheter that could be inserted through the urinary passage in a relatively pain-free manner. The solution lay in the creation of a hinged silver tube that was more flexible than the standard rigid metal versions of the era. However, this tube could also be stiffened by the insertion of a metal wire that lengthened and retracted by way of a turning screw. Although Franklin might not have been the first to conceive of this particular item, as flexible catheters had been around in Europe for some time, his is considered the first to be used in America.

Franklin’s many interests included plans for keeping the streets of Philadelphia well-maintained; to that end, he advocated for the installation of street lamps around 1757. He also proposed a design that improved on the existing globe lamps imported from London, which became murky as smoke collected within the enclosed glass. Franklin’s invention had a funnel at the top and vents below that enabled the passage of smoke, keeping the lighting sharp and preventing the need for daily cleaning. Additionally, his lamp consisted of four adjoining glass panes instead of one surrounding sphere, which meant that an accidental breakage would generally require the simpler replacement of separate panels instead of the entire glass shell.

Intrigued by a performance of the glass harp, in which upright glasses are “played” as moistened fingers trace around their rims, Franklin commissioned a London glassblower to build an instrument based on the same physical principles. The result was 37 glass bowls, fashioned in specific dimensions to produce distinct musical notes, that fit together on a horizontal iron spindle that could be turned with a foot pedal. Its name taken from the Italian word for harmony, the glass armonica gained a prominent following after its 1762 debut, with luminaries such as Mozart and Beethoven incorporating the instrument’s ethereal sounds into compositions.

“Franklin was terrific about advertising his inventions, and he shared his new musical instrument through performances, which made this invention very popular,” Carroll shares. “Having said that, it was difficult to play and about as expensive as purchasing a piano, so the armonica did not become a regular household instrument. There was also some bad press that its eerie sound caused mental instability, but Franklin was dismissive of these remarks.”

Usually depicted wearing glasses, Franklin’s later-life eyewear was yet another device born of innovative impulses. As he described (and sketched) in a May 1785 letter to London merchant George Whatley, Franklin had an optician fashion “double spectacles” that satisfied his need for lenses to accommodate both near- and farsightedness; by combining them into one piece, Franklin wrote, “I have only to move my eyes up or down as I want to see distinctly far or near, the proper glasses being always ready.” Although some historians question the timeline for when Franklin first donned what later became known as bifocals, and whether he deserves full credit as the inventor, he is generally believed to have originated them in 1784.