Question

Read the following passage adapted from an essay on nineteenth-century American science:

In the autumn of 1847, the island of Nantucket was a bustling whaling port, but two miles off its cobblestone streets, on the roof of the Pacific National Bank, a quiet observation was about to reshape American astronomy. Maria Mitchell, a twenty-nine-year-old librarian at the Nantucket Atheneum, spent her evenings sweeping the skies with a modest two-inch Gregorian reflector telescope purchased by her father, William Mitchell, who served as the bank’s cashier. On the clear, chilly night of October 1, 1847, at approximately 10:30 p.m., Maria positioned her instrument toward the northern sky and noticed a faint, nebulous object near the North Star, lying just below the star Polaris in the constellation Ursa Minor.

Unlike recognized stars, which appeared as sharp points of light, this object possessed a soft, hazy glow and lacked any discernible tail. Suspecting she had located a previously unrecorded comet, Maria immediately called her father to the roof to confirm the sighting. William recorded the object’s coordinates in his ledger, noting its right ascension and declination. Over the next two nights, Maria returned to the telescope to monitor the object’s position. By observing that the fuzzy mark had shifted relative to the background field of fixed stars, she confirmed that it was moving—a definitive characteristic of a comet in orbit around the Sun.

News of the discovery traveled quickly from Nantucket to the Harvard College Observatory, where director William Cranch Bond verified Mitchell’s observations. However, establishing Maria’s priority as the first discoverer proved contentious. Years earlier, King Frederick VI of Denmark had established a prestigious gold medal to be awarded to any astronomer who discovered a telescopic comet—one invisible to the naked eye. The strict regulations of the Danish prize required the observer to notify the British Admiralty or the Danish government immediately by the next available mail post. Because Nantucket was isolated from the mainland and post ships were delayed by autumn gales, Maria’s official letter announcing the comet did not reach Europe for several weeks.

During the delay, European astronomers, including Father Francesco de Vico in Rome and W. Dawes in England, independently sighted the same comet. Initial reports from the Royal Astronomical Society credited de Vico with the discovery, assuming his notification had arrived first. William Mitchell, determined to secure his daughter’s rightful place in scientific history, initiated an extensive correspondence with American statesmen and scholars, including Edward Everett, then president of Harvard University. Everett petitioned the Danish Minister in Washington, presenting William’s dated observatory logbook entries from October 1 as indisputable physical evidence of Maria’s prior detection.

After a thorough review of the logbooks and postal transit delays, King Christian VIII of Denmark (who had succeeded Frederick VI) officially awarded the gold medal to Maria Mitchell in 1848. The recognition made her the first professional female astronomer in the United States and the first woman awarded a European scientific prize of this distinction. The comet was officially designated C/1847 T1, though in popular science it became known as "Miss Mitchell’s Comet."

According to the passage, Maria Mitchell used which of the following instruments to make her initial observation of the comet on October 1, 1847?