CLARIFICATION--AN UPCOMING EXHIBIT AT THE NATIONAL POSTAL MUSEUM, "POSTED ABOARD R.M.S. TITANIC," IS SCHEDULED TO OPEN SEPT. 17 AND TO RUN THROUGH NEXT JUNE 12. THE EXHIBIT DATES WERE OMITTED FROM YESTERDAY'S CALENDAR LISTING IN HORIZON. (PUBLISHED 09/09/99)

FREDERICK DOUGLASS:

MAN OF THE WORLD

The Frederick Douglass National Historic Site, maintained by the National Park Service, is planning a two-day conference on the life of the African American author and statesman. Scholars from Europe and North America are to discuss Douglass from a global perspective, including his relationship with other countries and his approach to the Constitution. It's scheduled Thursday and Friday, Sept. 9-10, 9 a.m. to 4 p.m., at the Deptartment of Interior Auditorium, 1849 C St. NW. The conference is free, but reservations are required. 202-690-5185.

COSMIC QUESTIONS

John Bahcall and his wife, Neta, both of the Institute for Advanced Study at Princeton University, are to discuss "Unsolved Problems in Astrophysics" on Friday, Sept. 10, 10:30 a.m. The free lecture is in the Green Auditorium at the National Institute of Standards and Technology, Quince Orchard and Clopper roads in Gaithersburg.

301-975-4202.

WHITHER PRAIRIE DOGS

Among upcoming films and lectures scheduled every Friday at noon at the Smithsonian's National Museum of Natural History are a film chronicling the decline of prairie dog populations Sept. 10, a lecture on the ancient Olmec civilizations of Mesoamerica Sept. 17 and a discussion of Arctic travels Sept. 24. All are free. 202-357-2700.

EVOLUTION VS. CREATION

The Kansas Board of Education's recent ruling on teaching evolution makes timely an upcoming talk by Rob Boston, assistant director of communications for Americans United for Separation of Church and State. He is to discuss the threat to intellectual freedom posed by some of the most extreme efforts to introduce creationism into public schools at the expense of science. The free program, sponsored by National Capital Area Skeptics, is scheduled Saturday, Sept. 11, 2 p.m., at the Bethesda branch of the Montgomery County Library, 7400 Arlington Road. 301-587-3827.

OVER AT GEORGE'S

George Washington's estate at Mount Vernon is hosting a colonial fair, Saturday and Sunday, Sept. 11-12, 9 a.m. to 5 p.m. Artists are to demonstrate 18th century crafts and sell such traditional wares as basketry, wood carvings, tin and iron work, leather workings, weavings and more. Authentic 18th century music and entertainment are featured. On Saturday, Sept. 25, 11 a.m., the annual program commemorating the dedication of the Slave Memorial at Mount Vernon is planned. Tributes to the contributions of early African Americans and a wreath-laying ceremony are scheduled.

703-780-2000.

CIVIL WAR TOURS

Torchlight tours of Fort Washington Park, exploring Civil War life in 1861, are scheduled Saturday, Sept. 11, at 8, 9 and 10 p.m. Admission is $6, and reservations are required. Civil War artillery demonstrations are scheduled Sunday, Sept. 19, at 1:30, 2:30 and 3:30 p.m. Admission is $4. The park is located at 13551 Fort Washington Rd. in Fort Washington. 301-763-4600.

CLOTH OF A CULTURE

Asante strip-woven cloth, or kente, is the most popular and well-known African textile. "Wrapped in Pride: Ghanaian Kente and African American Identity" is a new exhibition at the Smithsonian's National Museum of African Art, scheduled Sunday, Sept. 12. It examines the history and use of traditional kente cloth. Another related display, at the Smithsonian's Arts and Industries Building, explores the impact of contemporary kente production in other African countries and the United States. Along with the free exhibits, planned through January, are many educational programs, including a family day, panel discussion, lectures, storytelling sessions and weaving demonstrations.

202-357-2700.

COUNTY HISTORY

The Montgomery County Historical Society has planned several events in coming weeks, including a celebration of Montgomery County's 223rd birthday, Sunday, Sept. 12, noon to 5 p.m. Activities include local history exhibits and demonstrations. The free community event is to be held rain or shine at the society's headquarters, 103 West Montgomery Ave., Rockville. A walking tour of the Underground Railroad in Montgomery County is scheduled Saturday, Oct. 2, 9:30 a.m. The cost is $7 per person ($4 for society members), and reservations are required. Participants are to meet at the headquarters. 301-762-1492.

BUILDING ART

In conjunction with its "Tools as Art V" exhibition, the National Building Museum has scheduled a family program including a special tour showing how artists have turned ordinary tools into works of art. Participants can create their own artwork from nuts, bolts, washers and other construction material. The free program is scheduled Sunday, Sept. 12, noon to 4 p.m. No reservations are required. The museum is at 401 F St. NW, across the street from Judiciary Square Metro station.

202-272-2448.

YOU CAN DIG IT

Alexandria Archaeology has Family Dig Days planned on Saturdays, Sept. 18 and 25. Participants, who will assist in an actual "dig" near King Street Metro station, may select a session beginning at 10 a.m. or 1:30 p.m. Admission is $5, and children under 16 must be accompanied by an adult. Reservations are required. 703-838-4399.

STARTING WITH A BANG

Most scientists believe that the universe started with an explosion of energy. Find out what may have happened in the first moments of the "Big Bang" and how this affects the expanding universe today. On Tuesday, Sept. 21, 6 p.m., Michael Turner of the University of Chicago is to present a free talk called "Cosmology: From Quantum Fluctuations to the Accelerating Universe." It's at the National Academy of Sciences Auditorium, 2100 C St. NW, near Foggy Bottom/GWU Metro station.

202-334-1575.

MATHEMAGICS

Meet a math wizard whose mind works faster than a calculator. Arthur Benjamin, professor of mathematics at Harvey Mudd College and a performer of mental arithmetic tricks, is to present a free program called "Mathemagics: The Art of Mental Calculating," Saturday, Sept. 25, 4 p.m. It's in Skinner Hall at the the University of Maryland, College Park. 301-587-3827.

ROCK CREEK PARK DAY

Celebrate Rock Creek Park's 109th birthday at an all-day party featuring slide shows, a geology tour, guest speakers, various children's activities and ranger-led programs for all ages. The free event is scheduled Saturday, Sept. 25, 9 a.m. to 5 p.m., at the Rock Creek Park Nature Center, 5200 Glover Rd. NW, off Military Road. Other events in September and October include numerous animal programs, sky watching activities and educational hikes. 202-426-6828.

BOOKS WE LOVE

More than 100 contemporary writers, including Joyce Carol Oates, John Barth and Ann Beatty, responded to this question posed to them by Ronald B. Shwartz: "What books have left the greatest impression on you and why?" Shwartz compiled their responses in a volume called For the Love of Books: 115 Celebrated Writers on the Books They Love Most and is to discuss it in a free talk Wednesday, Sept. 29, at noon. It's at the Library of Congress's James Madison Building, 101 Independence Ave. SE. 202-707-5221.

WITH LEWIS AND CLARK

Dan Botkin, professor of biology at the University of California at Santa Barbara, is to discuss Lewis and Clark's western route into the American frontier, noting how the explorers' knowledge of natural history helped them to overcome numerous obstacles. The free lecture at the National Zoological Park is scheduled Thursday, Sept. 30, 8 p.m. Reservations are required. At 7 p.m., Botkin is to sign copies of his book Passage of Discovery: The American Rivers Guide to the Missouri River of Lewis and Clark. 202-673-4801.

FARM BOUNTY

Fall Harvest Days at Carroll County Farm Museum are scheduled Saturday and Sunday, Oct. 2-3, 10 a.m. to 5 p.m. Activities include demonstrations of threshing, corn husking, ice cream making, butter churning and food preservation. Farm animals are to be on view, with numerous displays and musical entertainment. Admission is $4 for adults, $2 for children ages 7 to 18 and visitors 60 and older. Children under 6 are free. The museum is at 500 South Center St. in Westminster, Md. 1-800-654-4645.

THE FIRST MARYLANDERS

On Saturday, Oct. 2, 10 a.m. to 5 p.m., Historic St. Mary's City is to honor the Yaocomaco Indians' contribution to Maryland's culture and heritage with demonstrations of pre-colonial technology such as flint knapping, stone toolmaking, hide tanning and more. A recreated Yaocomaco hamlet, including a long house and a smaller family lodging, are a permanent part of the museum. Historic St. Mary's City is located on Route 5 in Southern Maryland. Admission is $7.50 for adults, $6 for students and seniors and $3.50 for children ages 6 to 12. 1-800-762-1634.

It's a Puzzle

The first 10 readers who provide the correct solution to the adjacent puzzle will receive a literally priceless Horizon T-shirt and a brief mention in the next issue.

Send replies by e-mail to horizon@washpost.com or by letter to Horizon, The Washington Post, 1150 15th St. NW, Washington, D.C. 20071. We cannot accept answers by telephone.

The Buck Stops Where?

Three men on a journey stopped overnight at a rooming house for lodging.

The desk clerk told them that there was only one vacant room, No. 205, which they could have for $30. The three men agreed. Each gave the desk clerk $10 and then went up to the room.

Some time later that evening, the desk clerk remembered that the price for the room had been reduced to $25 the previous week. So he took five $1 bills out of the cash register and told the bellhop to take them to the men in Room 205 because they had been overcharged by that much.

On his way to Room 205, the bellhop figured that the men did not know that they had been overcharged, so he put two of the five $1 bills in his pocket.

When he arrived at Room 205, the bellhop told the three men that the price for the room was only $9 each instead of $10. He gave each man a $1 refund.

So each of the three men paid only $9 for the room, making a total of $27. The bellhop kept $2 more, totaling $29.

Where is the missing dollar?

Suggested by Bernard J. Freed

Bowie

Sent to the Bottom of the Sea

Titanic was more than just a luxury ship carrying passengers to their doom on its maiden voyage in 1912. It also was a "Royal Mail Ship," charged with delivering mail across the ocean. "Posted Aboard R.M.S. Titanic" is a new exhibition at the Smithsonian Institution's National Postal Museum that examines this seldom-recognized function of the great ship.

When Titanic sunk, about six to nine million pieces of mail went with her. The exhibit, scheduled through June, focuses on heroic measures taken by the ship's mail clerks, all of whom perished, to save this valuable cargo. Personal artifacts belonging to the clerks, some found on their bodies, are displayed as their stories are told. Video film footage of the mail room, also shown in the exhibit, reveals that sacks of mail survive nearly 90 years later.

The Postal Museum, located at 2 Massachusetts Ave. NE, next to Union Station, is open daily, 10 a.m. to 5:30 p.m. Admission is free. 202-357-2700.