Standing more than 8 feet tall in the Anthony J. Drexel Picture Gallery at Drexel University is a clock that not only gives the time and date, but also offers the moon's phase, the position of the sun and the moon in the zodiac, the placement of planets, the moon's orbit around the Earth, and the equation of time in order to sync the clock with the sun. It can also play 10 different songs at intervals throughout the day.

What makes the Astronomical Musical Clock so special is not fancy interior electronics and satellite connections, but that its construction was started in 1770 and was completed in 1773 by David Rittenhouse, one of Philadelphia's leading mathematicians, clockmakers, and astronomers. He was also the second president of the American Philosophical Society after Benjamin Franklin's death.

"It is the demonstration that this kind of engineering and development of machinery was possible in the country so early on" that makes this grandfatherlike clock so special for Baruch Blumberg, president of the society. "There were doubts that the United States could achieve the kind of technical engineering and level that was present in Europe at the time. And I think this was an outstanding example that this could be done here - and was done."

With only minor changes to the clock's inner workings throughout the years, this work of art, with more than a thousand pieces, is a great original example of Rittenhouse's mastery of clockwork and the care and delicacy that went into the creation of his clocks. It is one of only three known still-functioning Rittenhouse astronomical clocks.

The Drexel clock, with its miniature operating model of the solar system, called an orrery, and its many technical dials, is considered by some historians to be the most important clock in America.

In the spring, Ron Hoppes, a 1960 Drexel graduate, published a book about the clock, with the American Philosophical Society, called The Most Important Clock in America. While the clock was being conserved by Eric Wilson, Bruce Forman, and Hoppes a few years ago, he had unparalleled access to its inner operations.

"As soon as I heard about [the idea for the book] and talked to Ron, I wanted to bring it to our committee on publications," said Mary McDonald, the Philosophical Society's editor. "They were all very anxious to see it published. It's the type of book the society is proud to publish, because it's very scholarly, and it has a lot of good information for people."

The work highlights some history of Rittenhouse and this clock, and then delves into the timepiece's more technical engineering aspects.

"I was always interested in the mechanical aspects, but I could never find anything out," Hoppes said. "During the restoration, I was able to get the mechanical details - that's how I came to write this book about the clock."

According to Hoppes, the clock does things that he, a member of the National Association of Watch & Clock Collectors Inc. since 1975, and many others have never seen.

The equation of time, for instance, is one aspect unique to this clock. Before satellites and advanced mechanisms were used to set the time on clocks, one would have to read a sundial, then set the clock to the sundial's time. But due to many factors, only twice a year would sun time be the same as clock time. It was typical to include an equation of time, which would alter the inputted sun time to match up with the actual time.

"Usually, it's done with a kidney-shaped dial with a follower arm," Hoppes said. "The profile of the dial is what moves the hand back and forth. [Rittenhouse] did it with a small mechanical computer, though. He knew what features of the Earth changed the dial."

Rittenhouse used gears that could compensate for the Earth's tilt on its axis and the position of the Earth relative to the sun.

Hoppes also wondered what happened to the date dial on leap years. While he believed it would have to be physically moved, Rittenhouse had actually set the dial to rotate at 365 and one-quarter days so that every four years it would be in sync again.

Jacqueline DeGroff, curator of the Drexel Collection, wrote a biography of Rittenhouse included in the book. She also oversees the clock on a daily basis.

"When Ron said he was going to approach APS, I thought that was a wonderful thing, and the best organization," DeGroff said, "because Rittenhouse had such a long history with them."

Rittenhouse served as librarian, secretary, and vice president under the philosophical society's first president, Benjamin Franklin. When Franklin died in 1790, Rittenhouse became president.

"He was a very important figure in the early history of the country," Blumberg said. "He kept the society going at a very important time. He maintained interest in the society while he was president for quite a long time."

The clock itself has a long and intricate history. Although Rittenhouse's public life was at a high point, the clock was built during a time of great personal distress. His first wife, Eleanor, died during childbirth in December 1770. He married Hannah Jacobs two years later, and they had a child who died in infancy.

He built the clock for Joseph Potts for $640, or about $17,000 by today's prices. But it is unclear whether the clock ever reached Potts, and in early 1774, another member of the society, Thomas Prior, bought the clock. He is considered the first owner of the device, and his name can still be seen etched inside the cabinet door.

For the next century, the clock was passed down through important Philadelphia residents until it was donated to Drexel in 1894 by the widow of George Childs, the co-owner, with Anthony Drexel, of the Philadelphia Public Ledger.

The Picture Gallery is open free to the public from 3:30 to 5:30 p.m. Monday through Friday at Drexel University's Main Building, third floor, 32d and Chestnut Streets. For more information:
Contact staff writer Jeff Davidson at 215-854-4193 or