CHAPTER EIGHT: Troubled Waters: London, 1757–1762

Franklin's scientific curiosity flourishes from 1744–1751, culminating in his revolutionary experiments with electricity and lightning. He invents the Pennsylvania Fireplace and urinary catheter, discovers fundamental principles of electrical charge, and proves that lightning is electricity—a discovery that leads to the practical lightning rod and makes him an international scientific celebrity.

Franklin's scientific work during this period was driven primarily by curiosity rather than profit; he famously declined to patent his inventions, believing in sharing discoveries freely. His inquiry into heat absorption by dark fabrics exemplified his method: beginning with pure intellectual curiosity, then seeking practical application. In the early 1740s, he designed a wood-burning stove using principles of convection and heat transfer. Though initially popular, the Pennsylvania Fireplace proved less practical than hoped; the design required too-hot chimneys for proper convection, and most owners later modified it. He also devised an improved urinary catheter for his ill brother John, featuring a flexible design with an internal wire and collapsible mechanism. Franklin's study of northeastern storms revealed a counterintuitive discovery: while their winds blow from the northeast, the storms themselves travel from southwest to northeast—a breakthrough later hailed as the beginning of weather prediction science. His most celebrated work began in 1743 when traveling showman Dr. Archibald Spencer's electricity demonstrations captivated him. By 1747, Franklin commenced systematic experiments with a glass tube from his Library Company, discovering that electricity was not created but collected and could flow between charged bodies. He coined lasting terminology—positive, negative, battery, conductor—and formulated the single-fluid theory of electricity and the law of conservation of charge, concepts fundamental to physics for centuries. He identified "the wonderful effects of points," noting that pointed metal objects drew electrical charge more effectively than blunt ones. In November 1749, Franklin noted twelve striking similarities between electrical sparks and lightning, leading him to hypothesize that lightning was electricity and that pointed metal rods could draw its charge. He proposed the experiment in letters to Peter Collinson in 1750, published and translated into French by 1752. French scientists led by Comte de Buffon and D'Alibard performed the experiment first in May 1752 at Marly, drawing sparks from a storm cloud with a 40-foot iron rod. Franklin, unaware of the French success, conducted his own famous kite experiment in June 1752 with his son William, using a silk kite with a pointed wire and a key attached to a wet string to draw sparks and collect charge in a Leyden jar. He delayed public reporting until October 1752, published first in his Pennsylvania Gazette. The delay prompted historical debate, but meticulous analysis by I. Bernard Cohen confirms Franklin likely performed the experiment in June, before hearing of the French tests. Franklin's reluctance to report immediately reflected his customary practice of preparing full accounts before publication, fear of ridicule if initial findings proved wrong, and possibly his desire to coordinate announcement with his new almanac edition. He subsequently convinced Philadelphia to erect grounded lightning rods on high buildings—apparently the world's first for protection—and installed one on his own house with an ingenious storm-warning device using bells. Religious circles, particularly the Abbé Nollet, criticized the lightning rod as presumptuous, but most of the world quickly adopted the technology. Franklin received honorary degrees from Harvard and Yale in 1753 and became the first person living outside Britain to receive the Royal Society's Copley Medal. His practical contributions—the single-fluid theory, distinction between insulators and conductors, concepts of grounding and batteries—transformed electricity from parlor trick to science. Though not a rigorous theorist like Newton or Galileo, Franklin's experimental pragmatism and focus on useful applications proved foundational to physics. The chapter concludes with Franklin's conviction that public service ranked equal to scientific pursuits; he soon would apply his experimental method to statecraft.