Newswise — Depictions of scientific experiments hold significant importance in science education and the spread of scientific knowledge to the public. Validating the saying that "a picture speaks volumes," these portrayals of renowned experiments persist in the memory of learners and establish the quintessential renditions of the scientific method. Archimedes in the tub unveiling the buoyancy law; Newton bending sunlight with a prism, formulating the tenets of contemporary optics; Mendel nurturing peas, establishing the bedrock of genetics – these exemplify a handful of widely recognized instances.
Numerous of these portrayals convey inaccurate information, either due to the experiments never occurring or being conducted differently. Individuals attempting to replicate them based solely on the illustrations may encounter no results or potentially face perilous consequences.
A research project, funded by FAPESP and carried out by Breno Arsioli Moura, a researcher from the Federal University of the ABC (UFABC) in São Paulo state, Brazil, examined representations of a renowned experiment involving Benjamin Franklin (1706-1790). In this experiment, Franklin flew a kite to harness electricity from a thundercloud.
Franklin, a prominent figure in the American Revolution and the inaugural United States Ambassador to France, played a crucial role in embodying the principles of the Enlightenment during the 18th century. As a Deist and Freemason, he excelled as a renowned thinker with diverse interests encompassing religion, philosophy, politics, and moral and social reform. Additionally, Franklin stood out as one of the leading inventors and scientists of his era. Among his notable scientific accomplishments, the kite experiment stands as his most celebrated achievement. Moura, in analyzing seven illustrations of this event published in the nineteenth century, shared insights with Agência FAPESP.
Indeed, Moura pointed out that the kite experiment was actually a simplified version of another experiment conceived by Franklin in 1750, now known as the "sentry box" experiment. This experiment involved setting up a sentry box atop a tower, steeple, or hill, with a person standing inside on an insulating platform made of wax. A long iron rod, about 10 meters in length and sharply pointed, would be inserted into the platform [refer to the first figure in the gallery at the bottom of this page]. Franklin anticipated that the rod's tip would attract electrical charge from the clouds, and by bringing one's knuckles close to the bottom of the rod, sparks would be produced. Moura emphasized two important aspects: the experiment was not meant to be conducted during a storm to harness lightning strikes, and the rod was not to be grounded but secured by the insulating platform, allowing all extracted electricity to be stored within it.
Franklin's original proposal for the "sentry box" experiment remained as a concept on paper until a remarkably similar experiment was carried out by French researchers in 1752. The success of this experiment garnered even more international recognition for Franklin's contributions to the study of electricity. Upon learning about the French experiment, Franklin corresponded with an individual in England and mentioned that a simpler variation of the experiment had been conducted in Philadelphia, his place of residence. This simpler version was, in fact, the famous kite experiment. Moura highlighted this significant development in Franklin's work.
Franklin described the construction of the kite, which comprised two slender strips of cedar forming a small cross. These strips were of sufficient length to extend to the four corners of a large, delicate silk handkerchief when stretched out. At the top of the upper stick of the cross, a sharply pointed wire was securely attached, extending a foot or more above the wooden framework. The underlying principle behind the kite experiment remained consistent with the sentry box proposal. A key was affixed to the end of a silk ribbon, which, in turn, was tied to the end of the string. It is worth noting that silk serves as an insulator in this setup.
Moura further elucidated that the experimenter would hold the apparatus by the silk ribbon, allowing the electricity captured by the kite from the clouds to be silently conducted down along the string and stored in the key. Similar to the sentry box experiment, the kite remained insulated and was not grounded. By bringing a finger or knuckle close to the key, the experimenter could elicit sparks, demonstrating the presence of stored electrical charge.
Similar to other natural philosophers of the eighteenth century, Franklin conceptualized electricity as a fluid that accumulated and could subsequently be discharged, flowing from one location to another. In laboratory settings, this electric fluid could be generated by rubbing a glass tube with a piece of leather and stored in a Leyden jar, a device invented by Dutch scientists in the mid-century. The underlying concept behind both the sentry box and kite experiments was to demonstrate that this electric fluid could also be extracted from the clouds. Franklin displayed a keen interest in the physics of cloud electrification and various facets of meteorology, finding fascination in these areas of study.
Indeed, Franklin held the belief that seawater contained a significant amount of electric fluid. According to his understanding, when seawater evaporated to form storms high above the ocean, it carried this electric fluid along with it. Consequently, Franklin hypothesized that the clouds themselves became charged with electricity, contributing to their electrical properties during storms. This perspective on the presence of electric fluid in seawater and its influence on cloud electrification was part of Franklin's scientific outlook.
According to Moura, Franklin's writings lack specific details regarding whether he personally conducted the kite experiment or if it was performed by someone else. However, there is evidence suggesting that the experiment did take place. Another account of the experiment emerged 15 years later, in 1767, within a book titled "The History and Present State of Electricity" authored by Joseph Priestley. It is worth noting that Franklin assisted Priestley in obtaining materials for the book, indicating his agreement with its contents. Priestley's account provides a more extensive description and mentions the participation of Franklin's son in the experiment. However, it deviates from the original 1752 account on several aspects, highlighting discrepancies between the two versions, as highlighted by Moura.
Moura's analysis of the illustrations portraying Franklin's kite experiment suggests that they were influenced by Priestley's account. Many of these illustrations depict Franklin alongside his son as a young boy, despite the fact that his son would have been 21 years old at the time of the experiment. Furthermore, numerous illustrations contain significant errors. For instance, they show the experiment taking place in open air, despite Franklin's explicit instructions that the experimenter should be positioned in a door, window, or under some form of cover to prevent the silk ribbon from becoming wet, which would make it conductive. Additionally, many illustrations depict the kite being struck by lightning or lightning bolts appearing in close proximity, even though Franklin's intention was not to attract a lightning strike towards himself. Most illustrations also fail to depict the silk ribbon meant to insulate the kite, with Franklin simply holding the string. Such an arrangement would have grounded the kite, compromising the integrity of the experiment. Moura also mentioned one illustration that shows Franklin holding the key near or on the string, a detail that is not supported by any historical accounts. These observations highlight the discrepancies and inaccuracies present in the illustrations of Franklin's kite experiment.
Moura emphasized the need for caution and critical evaluation when using illustrations, particularly in science classes. He stressed that these illustrations carry messages that can be easily misunderstood or lead to incorrect interpretations, both in terms of historical accuracy and scientific understanding. Due to the lasting impact of visual representations on the viewer's memory, any errors they convey can be challenging to rectify. Therefore, it is essential to approach illustrations with a critical mindset and ensure that they are used responsibly to avoid perpetuating misconceptions or confusion.
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