 Ball Clocks 
If you have something to
add, please send e-mail to jimw@chilton.com. People
occasionally write asking if I know of any other sources for ball
clocks. Sorry, I don't; if I did I would put it on this page! Please
let me know if you find any other sources.
What Is A Ball Clock? The clock described in the ACM programming problem has three tracks that hold ball bearings. Once a minute, a rotary arm lifts a ball up and drops it in a channel where it rolls onto the topmost track. When five balls have accumulated in the top track, the weight of the balls tips the track down. One ball rolls down to the middle track, and the rest roll to the pickup queue at the bottom of the clock. The middle track thus has a ball for every five minutes of time. When the twelfth ball rolls onto the middle track, it dumps one ball onto the bottom track and sends the rest to the pickup queue. So the bottom track has a ball for each hour. Each track is labeled with hours or minutes. To read the time, you look at the bottom track and read off the hour, then you add the minutes shown on the top two tracks. Clock Vendors September 2000 Flash: They're back! The fall issue of the Edmund Scientific catalog includes the latest reincarnation of the Arrow clock. A new twist is that the clock can be run off either A/C or batteries. (I guess the batteries are for when you take the clock with you camping.) To order, call 1-800-728-6999 and ask for item number #V82-445, or visit their website at www.scientificsonline.com. April 2000 Update: Around 1997, some factory in China must have produced a single large run of ball clocks, apparently using the same molds as the Arrow clocks that were sold in the 1970s and '80s. The clocks were available in novelty stores everywhere, but they eventually sold out and are now hard to find. You can check the vendors listed below, but I think it's unlikely that any of them have any clocks left. Your best bet is to check Internet auction houses such as eBay, Yahoo! Auctions, or Amazon Auctions. On eBay, search for "ball clock" or, if you get tired of looking at spherical clocks and clocks with balls in place of numbers, try a more specific search. For the record, here's the information about places that used to sell ball clocks:  Michael Robb wrote on April 9, 1997, and gave the following source for a ball clock:
The catalog number is 11016 and the price is $49.98. I actually bought one of
these. It's called "As Time Rolls On" and is made of plastic in China.
It works fine, but beware that it's not a quiet timepiece. Every
five minutes it sounds like someone is rattling a box of marbles. My
boys, who are 6 and 9 years old as I write this (fall 1997), adore the
clock. They especially love watching the "big dump" at 1:00, when all
the balls roll back to the pickup queue.
Ron LaPedis wrote on April 15, 1997 and said that The Sharper Image in California sells the ball clock pictured on the ball clock problem page. It's apparently the same "Time Rolls On" model, but they sell it for $40. Their phone number is 800-344-4444. Ask for item number WR102. 
Ron also gave the following source:
Still another reference from Ron is:
They sell parts for the Arrow Mfg. ball clock made in the 1970's and 80's. Although the website claims they don't sell complete clocks, Bob Swan says they do and that he bought one from them. (Timesavers also sells the "Golden Hour Mystery Clock," something I remember from my grandparent's house. It has the hands mounted in the middle of a round pane of glass with no visible linkage driving them.) David
MacMillan says that Steven Berger of Timesavers has indicated that a
similar clock, constructed of wood, is available in Europe for DM175.
Public Clocks George Rhoads has created a number of rolling ball sculptures (some of which may be clocks) that are installed in public places. For more information, visit George's web site, or see the article "Clumper Upper to Wok Dumper to Chute to Helix to Block" in the October 1988 issue of Smithsonian magazine. Here's an excerpt:
Another installation is (or was) at The Tech Museum of Innovation in San Jose, California. What A Clock! My friend Jeff Chilton brought this amazing creation to my attention: The Clock of the Long Now. It's a clock that eats Y2K problems
In a time when we seldom
think past the next weekend, and practically no one ever thinks past,
say, their grandchildren's lifetimes, it's a mind-bending experience to
consider posterity on the Long Now scale. Yes, elaborate clocks and
modern Rosetta Stones aren't that important by themselves, but they are
important if they catalyze a hopeful optimism that maybe we'll still be
around as a species in 10,000 years and that perhaps we should be
striving toward that goal instead of living day-to-day with a sort of
Malthusian pessimism.
Jeff said one of the early
designs involved rolling balls (obligatory on-topic connection), but
they seem to have disappeared from the current design. I particularly
like the equation of time cam, a deeply mathematical three-dimensional
surface that could hold its own as sculpture in a modern art museum.
Further Reading Harley Mayenschein invented the ACM-style ball clock in the 1970s and founded the Idle Tyme Corporation in 1978, which manufactured ball clocks made of wood. I learned this when Patrice Gunville, Harley's daughter, wrote me in July 1998 to correct my mistaken claim that George Nelson invented the ball clock. (Nelson's clock is just a conventional clock with balls on radial spikes replacing the numbers.) Her letter has more information about her father and the early history of his ball clock. David MacMillan has an excellent and extensive website devoted to Rolling Ball Sculptures, Clocks, Etc. His site has pictures of ball run sculptures by George Rhoads and others, descriptions and pictures of many types of ball clocks (including excerpts from Harley Mayenschein's ball clock patent), and numerous links to related sites. David has even set up a mailing list for the discussion of ball clocks and sculptures. Helge Rustad has built two ball clocks, a large one made of Lego and a smaller one built of wood, plus several other delightful homemade projects (including a ping-pong-ball computer). See his home page for pictures and more information. David Ralston, a sculptor and clockmaker, has built a large ball clock out of stone billiard balls and brass stock. Another amazing clock, the Sand Wheel, is something like an endless circular hour glass. Tod Flak built a very nice looking ball clock of his own. Entirely handcrafted out of cherry wood, except for the custom-programmed 8031 microcontroller! (Todd's site has been dead for a while, but maybe it will resurface some day.) Stuart Singer has a page devoted to ball clocks, including some product literature from the old Arrow clocks and information about the new battery-powered series of Time Machine clocks, which includes a seconds indicator.
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