The March-April issue of American Scientist is now available on the Web; paper copies should be on their way soon. My column is about hump yards and turnouts and wyes—in other words, about algorithms for railroad workers. “Computing with locomotives and box cars takes a one-track mind.” There’s a small puzzle near the end of the column. You’re welcome to post comments, complaints and solutions here.
In the new issue I also recommend a “Macroscope” article on Avogadro’s number by Ronald M. Fox and Theodore P. Hill of Georgia Tech. For those who have forgotten their chemistry, Avogadro’s number is the number of molecules in a mole of a substance (an amount in grams numerically equal to the molecular weight). Specifically, NA is defined as the number of carbon atoms in 12 grams of carbon-12, and its value is roughly 6.02 × 1023. Fox and Hill suggest turning the definition upside-down: Instead of trying to count the atoms in a gram, define the gram as a certain number of atoms. They have a specific number to recommend: 602,214,141,070,409,084,099,072. I invite you to deduce what’s so special about this particular number and why they favor it over other candidates in the same range.