Consider, if you will, that classic breakfast cereal, Raisin Bran. A Raisin Bran raisin is heavier than a Raisin Bran flake. Logic dictates that heavy things ought to fall to the bottom of the box. However, when we examine a box of Raisin Bran, we find to our surprise (and delight, of course, because we love raisins) that the raisins are evenly distributed throughout! How so? Are the raisins cunningly charged with mutually repellent magnetic forces so they space themselves uniformly? Or does Kellogg’s just put the raisins in last, counting on the ham-handedness of the shipping clerks to jostle them evenly through the cereal by the time it gets to your breakfast table? –Ed, Los Angeles

An idle mind, Edward, is the devil’s workshop. There’s no great mystery. Bran flakes are fairly dense, and they pack themselves close together in the package, preventing the raisins from moving. Kellogg’s simply mixes the flakes and raisins together when filling each box, and they stay that way during shipping without much internal migration.

A more interesting question along these lines, if you don’t mind my saying so, is this: how come, if you’ve got half a jar of shelled peanuts that’s been knocking around the kitchen for a while, the big pieces wind up on top and the little chunks and crumbs wind up on the bottom, contrary to expectation? Aristotle, I think, used to wonder about this. Actually there are two reasons. First, while a crumb weighs less than a big piece, the crumbs and chunks in aggregate weigh more per unit of volume, because the big pieces have lots of space between them and the crumbs don’t. Then we have the mechanics of sifting to think about. It’s easy for the crumbs to slip down past the big pieces to the bottom of the jar, but the big pieces don’t make much headway sinking into the densely packed small stuff. So it’s crumbs at the bottom, nuts on top. Maybe now you have some insight into modern corporate life.

Pretty soon we’ll be starting a new decade (since, as all educated people realize, decades start with a one, not a zero). This got me wondering. AD 1991 means “in the year of our Lord 1991.” When did this system start? I assume that after Christ was crucified, it wasn’t just a matter of people saying, “Truly, he was the Son of God. Better renumber the calendar.” What numbering system did Christ’s contemporaries use? –Rob Rodi, Chicago

Good question, Robster, but first let me congratulate you on getting the facts straight on the new decade not starting until the end of 1990. When I pointed this out last New Year’s, one woman cried out in anguish, “My God, you mean it’s still the 80s?” She had my sympathy, but facts is facts.

The Christian system of year numbering was invented in what we now know as AD 525 by a monk named Dionysius Exiguus, who had been asked by the pope to work out a better way to figure when Easter occurred. There was probably a simpler way of doing this than renumbering the entire calendar, but I guess Dionysius got a little carried away. Surprisingly, considering it was the maker of the heavens and the earth who was the honoree, it took a while before the AD method caught on. The popes didn’t use it routinely until the 10th century AD and the Greeks not until the 14th century.

One defect of the calendar is that Dionysius miscalculated the date of Christ’s birth. The somewhat incongruous result was that by modern calculation Christ was born about 4 BC–meaning Before Christ, of course. But hey, we all make mistakes.

In Christ’s time the Romans numbered their years anno urbis conditae, from the founding of Rome. Christ was born circa 750 AUC. Other systems of reckoning were also used from time to time. One of the odder ones, in common use during the middle ages, was called the indiction. It was a rotating 15-year cycle–you got to 15, you started over again at 1. No doubt this bespeaks a rather static conception of history–none of this modern idea of progress, you know. But at least they weren’t bothered by people getting nostalgic for the 60s.

Art accompanying story in printed newspaper (not available in this archive): illustration/Slug Signorino.