Unlike alarm clocks, which repeatedly strike a single bell to mark the passing of a given moment in time, chiming clocks utilize multiple bells or chiming rods to create their brief melodies, which are often set to play at 15-minute intervals. So-called "ting-tang" clocks have just two bells while other antique chiming clocks might have as many as eight, the number needed for a complete musical scale. Musical clocks, which date from as early as the mid-16th century, differ from chiming clocks in that their mechanisms are separate from the clock's "going" train, the set of pinions and toothed wheels that turn the clock's hands. Indeed, musical clocks can almost be thought of as music boxes attached to clocks. In addition to bells, some musical clocks play flutes (the cuckoo clock is a prime example of a fluted clock) while others produce organ sounds. By the 18th century, respected composers were actually writing original melodies for musical clocks, a precursor, perhaps, to the modern practice of sampling snippets of melodies and catchy beats for digital ring tones. The songs and tunes played by vintage and antique chiming clocks are sometimes ones that were popular at the time of a clock's manufacture, but many clocks simply play the Westminster Quarters, the sequence associated with Big Ben, which is located at the Palace of Westminster in London. Whatever the melody, the sounds are pinged out by small hammers that strike half bells (nested into each other to save space) or chiming rods in an order dictated by the clock's chiming train. On some clocks, the chiming train is wound separately from the "going" train, but on other clocks the "going" train drives everything. Almost any clock can be fitted to chime. There are chiming mantel clocks, grandfather clocks, carriage clocks, regulators, and banjos. Sessions made chiming clocks, as did Seth Thomas, Ansonia, and Gilbert. Chiming clocks were favorites of French clockmakers, as well as those in German and Austria. An early example of a tall American chiming clock is the model made some time between 1773 and 1775 by Benjamin Willard of Grafton, Massachusetts. Standing more than 7 feet tall and made of American cherry and white pine, this clock features 10 brass bells, each of which is struck by a brass hammer triggered by a rotating music barrel, also made of brass. An eleventh hammer not triggered by the music barrel strikes an eleventh bell on the hour, and like the "going" train and chiming train, this movement is wound separately. A key feature of this Willard clock was its ability to play a different tune for each day of the week, with a "Psalm" melody on Sunday. Another early American chiming clockmaker was David Rittenhouse of Philadelphia, whose contribution to chiming-clock technology culminated in 1774 with a grandfather clock that stood 9 feet tall. Bettering Willard, Rittenhouse's "masterpiece," as it came to be known, could play 10 melodies on 15 bells—if one so desired, four of these melodies could be played simultaneously. But Rittenhouse was propelled by a range of non-clock passions and abilities, which troubled some of his contemporaries. For example, in 1778, none other than Thomas Jefferson wrote to Rittenhouse in an attempt to persuade him to shed his civic-mindedness for clockmaking. "Nobody can conceive that nature ever intended to throw away a Newton upon the occupation of a crown," the future president wrote, comparing Rittenhouse favorably to the great Sir Isaac Newton. Its flattery notwithstanding, the letter failed to convince its reader. Before long, Rittenhouse became professor of astronomy at the University of Pennsylvania (1779 - 1782), and a decade after that, he was named the director of the U.S. Mint in Philadelphia (1792 - 1795).