Well, Garrison Keillor says:
Today is the birthday of the American astronomer, mathematician, and surveyor David Rittenhouse, born near Germantown, Pennsylvania (1732). He built one of the first telescopes in America, and used a real spider's silk to form the crosshairs in the eyepiece. He used his telescope to study the transit of Venus, and determined that the planet has an atmosphere. He was also a surveyor, and determined part of the boundary between Pennsylvania and Maryland, although he didn't enjoy the work. He said, "I found it a very laborious affair; being obliged, singly, to go through a number of intricate calculations." During the Revolutionary War, Rittenhouse worked as a weapons engineer, improving designs for cannons and rifles. George Washington named him first director of the United States Mint in 1792. Benjamin Franklin and Thomas Jefferson held Rittenhouse in high regard, and Philadelphia's Southwest Square was renamed "Rittenhouse Square" in his honor in 1825.