In June 3, 1769, after months of planning, the skies that had been cloudy for several days cleared over East Norriton, Pennsylvania. David Rittenhouse waited nervously for the moment when Venus would briefly become visible as it passed across the sun. This transit was an extremely rare event and according to computations by Edmund Halley, offered the opportunity to calculate the distance between the sun and Earth. The stakes were high as another opportunity would not occur for 105 years. As crowds of onlookers watched, David Rittenhouse’s team prepared to record this event, and then just before the shadow touched the disk of the sun, David Rittenhouse fainted from exhaustion. Fortunately, he prepared well and his team was able to collect some of the best data on the Transit of Venus.
Rittenhouse was increasingly known for his astronomical abilities. William Smith, the first provost of the College of Philadelphia, selected him to lead the North American effort of this international scientific collaboration that would leverage the size power of the British Empire to take parallax measurements as Venus passed between the Earth and the Sun. The Venus transit of 1761 had not been visible from the British Colonies on the American Eastern Seaboard. This meant that the still relatively young American Philosophical Society of Philadelphia was eager to make a good showing in observing the 1769 transit. The American Philosophical Society acquired a grant of £100 to buy new telescopes and equipment for the 22 observation stations to be set up in and around Philadelphia and placed Rittenhouse in charge of the effort.
Rittenhouse was born in 1732 near Germantown. Farm life was arduous and offered no time for formal schooling, but Rittenhouse, armed with a curious mind and inspired by science, taught himself physics and math. After inheriting his uncle’s woodworking tools, along with a number of science books such as Isaac Newton’s “Principia,” Rittenhouse set out to make his livelihood away from farming. This led him to perfect his mathematical skills through surveying and clock building and to become an astronomer. The transit was without doubt a highpoint in his life as a scientist and so he invested an extraordinary amount of effort in preparing for the occasion. He built a temporary observatory on his land that he preceded to equip with the finest instruments, all of which he constructed himself. He designed and built a new super accurate clock with which to time the transit as well as a set of precision astronomical instruments. He worked long hours every day for a year preparing for the great event.
Unfortunately, just before the transit he became ill. As the team of three observers took their stations. Rittenhouse himself laid flat on the ground near the observatory so he could watch the path of the transit through his telescope as Venus passed directly overhead. As the actual shadow of Venus passed over the Sun (a transit is like an eclipse in that the planet cast a shadow which is visible at distance), Rittenhouse fainted. Weakened by illness and exhausted, he completely missed actual moment when the shadow passed over the disk of the Sun. His team, however was able to observe and record the transit without incident and Rittenhouse’s team actually produced the best transit observation results in the empire.
The Royal Society used Rittenhouse’s as well as other observations (most notably James Cook’s) to calculate the distance from Earth to the Sun to be 93-million miles. The published report of the transit was hailed by European scientists, forever cementing Philadelphia as the home of not one but two world renowned scientists (the other being Benjamin Franklin for his studies of electricity).
Michael Carver -- Historical Interpreter/Reenactor 