Mathematical Digest Short Summaries of Articles about Mathematics in the Popular Press "On the Teeth of Wheels," by Brian Hayes. American Scientist, July/August 2000, pages 296300. This article discusses an intriguing connection between number theory and the design of gears. While working on an earlier article about a variant on the wellknown Fibonacci numbers, the author came upon a number theory article that had been published in a clockmaker's journal. This led him to investigate the ingenious calculation methods developed by 19th century gear makers. These methods allow one to calculate the number of teeth needed on gears in a gear train to insure that the gears rotate at the correct rate. The computer has made these methods obsolete for gear design, but their value in number theory endures.  Allyn Jackson
