PHILADELPHIA (AP) _ Some 500 descendants of William Rittenhouse, who came to the New World in 1688, are gathering this weekend to celebrate being part of a family that boasts famous scientists, doctors and businessmen.

Harold Rittenhouse, a 10th generation direct descendant and chairman of the Rittenhouse Tricentennial Reunion, said his forefather - the first Mennonite minister in America - would be taken aback by the celebration.

''Being a simple person, it would have been a little bit overwhelming for him to come to a reunion like this,'' Rittenhouse said.

Family members from 26 states and Canada are expected to attend.

William Rittenhouse was born Wilhelm Rettinghaus in Germany in 1644. He went to Holland, where he may have learned his trade of papermaking, before coming to America, in part to escape religious prejudice in Europe.

He built what's recognized as the first paper mill in America in 1690 as part of a colonial village called RittenhouseTown, in what is now Fairmount Park in Philadelphia.

He became a Mennonite minister, preaching from a church in Germantown.

He had three children, two daughters and son, before he died, crippled from the back-breaking labor of working the mill, in 1708.

The family spans 12 generations and claims as many as 40,000 members, including admirals, governors, senators and judges.

David Rittenhouse, a great-grandson, was a leading astronomer, mathematician and clockmaker in colonial times. A Philadelphian who knew Thomas Jefferson and Benjamin Franklin, he became the first director of the United States Mint in 1792.

Other descendants include Maj. Gen. William Crawford Gorgas, a physician who helped conquer yellow fever, and Raymond Rubicam, one of the fathers of modern advertising.

The Rittenhouse story is documented in the last family history written in 1893, also the year of the last large reunion.

''The possibility of updating or redoing our family history is a strong inducement for me,'' Rittenhouse said. ''People say they have family memorabilia.

''We've had people say something like we have a deed from RittenhouseTown,'' he said. ''One person from Texas said they have a grand piano that has been in the Rittenhouse family.''

Rittenhouse began planning for the reunion in 1987 and sent out more than 2,000 invitations. He was pleased with the expected turnout of about 500 family members.

''Being the 300-year-reunion is a drawing card on its own - just being part of something like that,'' he said.