You probably have seen a “swinger” clock but never guessed how it worked. Most are small metal statues standing on a base while holding a long baseball bat, pendulum or other long, thin rod that is topped by a clock or a globe. It keeps time and the pendulum keeps swinging, but there is no sign of an electric plug or other power source.

The first “mystery clock” was made by a French magician, Jean Robert-Houdin, in 1845. Many other versions followed. Junghans, a German clock factory, made most of those seen today. Ansonia, an American clock company, also made these unusual clocks. The secret clock parts that kept the hands moving were even patented. The trick is that part of the base moves around slightly, keeping the pendulum swinging and moving the clock’s hands. Another type of mystery clock was made with two clear crystal disks with a clock hand painted on each. The disks turned with power from the base. Many copies of antique mystery clocks have been made.

The model with an elephant swinging the clock is a favorite that was originally made by Junghans but has been copied in China. Surprisingly, the original had an elephant made of white metal while the copies made before 1930 were bronze. Watch out. There are many copies sold today, and it is very difficult to tell old from new. There are swinger clocks with figures such as a boy with a bat, the Statue of Liberty, Diana, a cherub and even a kangaroo. Neal Auction Company recently sold a metal swinging elephant clock made about 1900, probably by Junghans, for $576. It had a bronze patina.

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Q. I’m looking for advice on selling a business card with Thomas Edison’s autograph on it. It’s the business card of Harry H. Harris and written on the back of the card in pencil is, “Signed around 1916 in presence of Harry Harris.” The card was given to me by Mr. Harris in 1972, when I was his paperboy. I was thinking of writing a brief description of how I got this and signing it in front of a notary public. Do you think that is sufficient authentication?

A. The value of an autograph is based on the importance of the signer and the rarity of his signature. Handwritten, signed letters sell for the highest prices. Autographed photos sell for more than just a signature in an album or on a card. Condition is also important. There are auctions that specialize in autographs, and they will tell you what they need in order to provide authentication. A written description of how you got the card would help. You can find more information about what determines the value of an autograph on Heritage Auctions’ website, HA.com.

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Q. I have a USO jacket worn by Miss USA 1992 when the girls traveled to entertain the troops during the Gulf War. Dick Clark, Ed Mahon and Steve Harvey all signed this jacket for Shannon Marketic, Miss USA 1992. Is there any value to it?

A. The USO, United Service Organizations, Inc., is a private, nonprofit organization founded in 1941 to support American troops and their families during World War II. The USO is best known for its tours of entertainers and other celebrities. They visit military bases at home and abroad in an effort to boost morale and connect the troops to home. The autographs and provenance of your jacket may add to the price it will bring. Auctions that specialize in celebrity memorabilia include Hake’s Auctions (Hakes.com) and Heritage Auctions (HA.com). There are also auctions of war memorabilia that might want to sell your jacket.

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TIP: A paste of baking soda and water can be used to clean old enameled cast-iron pots.

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Terry Kovel and Kim Kovel answer reader’s questions sent to the column. Send a letter with one question describing the size, material (glass, pottery), and what you know about the item. Include only two pictures: the object, and a closeup of any marks or damage. Be sure your name and return address are included.

By sending a question, you give full permission for use in any Kovel product. Names, addresses or email addresses will not be published. We do not guarantee the return of photographs, but if a stamped envelope is included, we will try. Questions that are answered will appear in Kovels Publications. Write to Kovels, King Features Syndicate, 628 Virginia Dr., Orlando, FL 32803 or email us at collectorsgallery@kovels.com