On April 8, 1872 Peirce was appointed by his father to the position of assistant in charge of pendulum experiments at the Coast Survey office in Washington DC. Benjamin was at that time superintendent of the Coast Survey. Charles moved to Washington with his wife Zina and retained that position until December. 1 He resigned from his position at the Harvard Observatory, where he had been appointed assistant in 1869, but continued working on his photometric researches until he published them in August 1878. 2 Arrived in Washington, on the 20th Charles wrote to his mother: “On clear nights I observe with the photometer; on cloudy nights I write my book on logic which the world has been so long & so anxiously expecting.” 3 He was working at the same time on the pendulum experiments, on his photometric researches, and on a book into which he was hoping to put his system of logic.