In Franklin’s Footsteps: Exploring the History of Physics in Philadelphia

Everyone knows about Philadelphia’s political history, particularly during the American Revolutionary War. Yet it is also rich with the history of physics, dating back to the colonial era. Let’s take an excursion to the “City of Brotherly Love and Sisterly Affection” and soak in some science vibes from the past.

History of physics permeates Philadelphia’s downtown street grid. Its four major city squares are named after personages with at least some connection to physics: Washington Square, named after George Washington (who was originally a surveyor); Logan Square, named after James Logan, who played a pivotal role in introducing Newton’s work to the colonies (including early editions of the Principia); Franklin Square, named after Benjamin Franklin, well known for his groundbreaking explorations of the physics of electricity; and Rittenhouse Square, named after David Rittenhouse, who made pivotal contributions to optics and astronomy.

It is on Logan Square, linked to the Benjamin Franklin Parkway, that we find The Franklin Institute, one of the many sites in Philadelphia that bears Franklin’s appellation. Franklin lived in Philadelphia from 1723 until his death in 1790 (aside from multiyear stays in London and Paris), and is therefore appropriately well honored. A large, classically styled building with a columned façade, The Franklin Institute houses one of the leading hands-on science museums in the United States, a collection of Franklin artifacts, and the Benjamin Franklin National Memorial.

In the center of the memorial is a six-meter-high statue of Franklin, sculpted by James Earle Fraser. Beyond the memorial is the science museum, which features numerous exhibits, including a 26-meter Foucault pendulum and a large steam train built in 1926. Outside the museum building is a Grumman Lunar Module, built for the Apollo program. Not associated with the institute, but still of interest, a monument to Polish astronomer Nicolaus Copernicus lies across Logan Square. In 2005, the Franklin Institute was presented with the first American Physical Society (APS) historic physics site plaque in recognition of Benjamin Franklin’s achievements.

Franklin’s connection with physics went at least as far back as 1746, when Peter Collinson, a prominent London merchant and member of the Royal Society, sent him a package that included a glass tube used for electrostatic experiments and an article by Swiss professor Albrecht von Haller that described what was then known about the field. Making great use of the tube and the article, Franklin embarked on an intensive exploration of the nature of electrical properties. During the late 1740s, Franklin reported to Collinson a number of spectacular insights about electricity, including a definition of the concept of positive and negative charge, and establishing that electrical attraction and repulsion can act over a distance rather than just through contact.

Another Philadelphia museum dedicated to Franklin is Franklin Court, the site of his former home and print shop, located near the corner of Market Street and Third Street. Although the original building was demolished in 1976, during the bicentennial of American independence, the ruins of the house’s cellar and foundations were excavated, and new structures were built to offer a sense of how it looked. An underground museum, free to the public, showcases Franklin’s achievements.

Several streets away from Franklin Court are other notable sites related to Franklin. Franklin’s grave is located in Christ Church cemetery near the corner of Fifth Street and Arch Street. It is a tradition to toss pennies on his grave marker for good luck. At Fifth and Vine Street is the entrance to the Benjamin Franklin Bridge. Within its entrance plaza stands a metal sculpture commemorating Franklin’s purported “kite and key” electrical experiment. Designed by Japanese-American artist Isamu Noguchi, Bolt of Lightning was erected in 1984.

David Rittenhouse, while certainly not as well known as Franklin, was another Philadelphia-based physics luminary. Adept at building mechanical devices, Rittenhouse set out in 1767 to build an orrery: a machine replicating the motions of the planets and moons in the solar system using Kepler’s laws as a guide. In 1769 he investigated the transit of Venus by constructing a modified refracting telescope to measure the exact time of the transit. The goal was to use observations of the transit around the world to obtain the distance from the Earth to the sun through the method of parallax.

In the 1780s, Rittenhouse constructed the first diffraction grating. By placing fine hairs parallel to each other, he produced a grating with about 250 lines per inch and created a distinct interference pattern with six bright spectral lines on either side. Borrowing optical instruments from Franklin, including a prismatic telescope and micrometer, he measured the angle to each spectral line and discovered integer ratios between the higher order and first order lines. In the 1790s, he investigated the effects of air density on pendulum irregularity and designed a suspended pendulum that was balanced such that the buoyant forces on either side cancelled out.

Rittenhouse was born in 1732 in an early industrial community, set on a stream, that was then outside the boundaries of Philadelphia. Later incorporated into the city, the restored enclave is now called Historic RittenhouseTown and is open for tours. In 1825, Philadelphia renamed what was previously called Southwest Square after him, and Rittenhouse Square soon became known as one of the fanciest locations in the city.

Both Franklin and Rittenhouse are honored at the University of Pennsylvania, where each played a role in its early history—the former with a statue and an athletic field, and the latter with the David Rittenhouse Physics Laboratory. Penn has played an important role in the history of physics, including the Nobel-Prize-winning work of physicists Robert Hofstadter (electron scattering in nuclei), J. Robert Schrieffer (superconductivity), and Raymond Davis Jr. (solar neutrinos).

Penn’s very first professor of physics, George Frederick Barker, was close friends with Thomas Edison and played a role in the commercial use of electricity. His donated collection of early Edison light bulbs is on display in the lobby of Rittenhouse Lab. Another early Penn physicist, Arthur Goodspeed, claimed to have been the first physicist to expose a photographic plate to x-rays (unknowingly, at first, before Röntgen’s discovery) and was a pioneer in their medical use.

So we see that there is far more to Philadelphia than just the Liberty Bell, Independence Hall, and the steps made famous by Rocky. No matter where you look, there are monuments to a grand history of physics discovery.