Saturday, May 23, 2009

Physics in Philadelphia

[This is an advanced excerpt of an article I will be publishing in June, called Philadelphia: Life, Liberty and the Pursuit of Physics (to appear in Physics in Perspective).]

Philadelphia's downtown district, called Center City, is laid out in a grid pattern with four squares. Interestingly, three of these squares, Logan, Franklin and Rittenhouse, have some association with physics.

James Logan was secretary to William Penn when Pennsylvania was founded. He was a lover of books and interested in all manner of scholarly topics, including physics. In 1709 Logan purchased a copy of the first edition of Newton’s Principia, and later he also acquired copies of the second and third editions, thus playing a pivotal role in introducing Newton’s work to the colonies. During a trip to London in 1710, Logan witnessed Newton performing an experiment before an audience at St. Paul’s Cathedral.

Benjamin Franklin made monumental contributions to the physics of electricity. In 1746, the London merchant and Fellow of the Royal Society Peter Collinson sent Franklin a package containing a glass tube used in electrostatic experiments and an article by the Swiss naturalist Albrecht von Haller describing current knowledge in the field, which sparked Franklin’s interest and led him to embark upon an intensive investigation of electricity. Franklin went on to define the concept of positive and negative charge, to establish that electrical attraction and repulsion of materials can act over a distance and not only by contact, and to enunciate the idea of conservation of charge. The most famous of Franklin’s experiments, however, was his lightning-kite experiment in 1752 in which he proved that lightning consists of an electrical discharge.

David Rittenhouse, as a child, demonstrated great mathematical and scientific aptitude, studying Newton’s Principia in English translation, building mechanical devices, and establishing his reputation as a maker of clocks and instruments on the family farm in Norriton, about twenty miles north of Philadelphia. His primary scientific field of study was astronomy, and in 1767 he built an orrery (solar system model) using Kepler’s laws as a guide. In 1769 he gained recognition as a leading member of the American Philosophical Society by using a refracting telescope he had made to measure the exact time of the transit of Venus. He also constructed the first diffraction grating.

So we see that three of Philadelphia's squares have a connection with physics. The next time you are in Philadelphia and find yourself passing Logan's Square's fountain, watching Franklin Square's carousel, or enjoying the sculpture in Rittenhouse Square you may wish to think about the accomplishments of their namesakes.